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Unmanned Aircraft System

Handbook and Accident/

Incident Investigation

Guidelines

“Air Safety through Investigation”

International Society of Air Safety InvestigatorsPark Center107 East Holly Avenue, Suite 11Sterling, VA. 20164-5405 January 2015

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3 Executive Summary

4 Foreword

6 Preface

7 Chapter 1 - Purpose and Structure of the Unmanned Aircraft System (UAS)Handbook and Accident/Incident Investigation Guidelines

8 Chapter 2 - Differences between Manned and Unmanned Aircraft

16 Chapter 3 - Augmentation and Supplementation of Existing InvestigativeCapabilities for UASs Investigations

26 Chapter 4 - Annex 13 to the convention on International Civil Aviation:Recommendations Relative to UAS Investigations

26 Chapter 5 - Data Fields Associated with UAS Operations Requiring Capture

28 Chapter 6 - UAS-Specific Air Safety Investigator Skills

29 Chapter 7 - Evidence Preservation Following Unmanned Aircraft SystemAccidents

29 Chapter 8 - UAS Investigation Procedural and Functional Considerations

APPENDIX

40 Appendix 1- Significant Aspects of the Draft Italian Unmanned AviationRegulations

42 Appendix 2 - Proposed Addition to U.S. Title 14, Code of FederalRegulations

44 Appendix 3 - Recommendations for Further Reading

46 End Notes

48 Index

TABLE OF CONTENTS

This Unmanned Aircraft System (UAS) Handbook and Accident/Incident Investigation Guidelines is published

by the Interna� onal Society of Air Safety Inves� gators and is adapted from the UAS Working Group report UAS Inves� ga� on

Guidelines as submi� ed to and approved by the ISASI Interna� onal Council on October 12, 2014. Its use is intended for profes-

sional air safety inves� gators and accident preven� on specialists. Copyright © 2015—Interna� onal Society of Air Safety Inves-

� gators, all rights reserved. Publica� on in any form is prohibited without permission.

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EXECUTIVE SUMMARY

The Unmanned Aircraft System (UAS) Handbookand Accident/Incident Investigation Guidelineswere developed by the ISASI UAS Working Group(WG). The ISASI UAS WG Terms of Reference di-rected participants to seek to accomplish the fol-lowing tasks:

1. Determine properties of unmanned aircraft sys-tems and their operations that differ from exist-ing aircraft.

2. Identify additional investigative capabilitiesthat may need to be developed or made more robustto support the investigation of UAS-involved acci-dents.

3. For Annex 13 to the Convention on Internation-al Civil Aviation, Aircraft Accident andIncident Investigation:

a. Determine the extent to which Annex 13definitions for the States of Design, Manufacture,Occurrence, Registry and the Operator can be ap-plied to unmanned aircraft systems, including theirground- and satellite-based components.

b. Assess the adequacy of current guidanceregarding determination of the State responsiblefor conducting the investigation of a UAS accident.

c. Document any need to recommendchanges to Annex 13 related to the above.

4. Identify a standard dataset that should be cap-tured for each UAS-involved accident.

5. Identify additional UAS-specific training re-quirements for air safety investigators based on theabove.

6. Identify additional regulations that may beneeded to create or preserve evidence relevant toUAS accidents.

7. Make recommendations to the ISASI Councilregarding the best means of addressing the aboveto other ISASI Committees and Working Groupsfor appropriate action.

* * * * *

Key operational and physical differences betweenmanned and unmanned aircraft that may drive ad-

ditional investigative personnel, training or equip-ment requirements are:

The lack of a pilot aboard the unmannedaircraft, meaning the aircraft’s condition,trajectory and surrounding airspace can-not be directly perceived by its pilot incommand (PIC).

Reliance on radio-frequency (RF) spec-trum and continuous connectivity be-tween ground control station and aircraftfor safe operation, meaning a UAS pilot’scontrol over their aircraft is subject todisruption of a type not experienced inmanned aircraft;

The varying and sometimes extremely lim-ited abilities different types of unmannedaircraft have to separate themselves fromother aircraft (meaning operation under“visual flight rules” as currently constitutedis not always possible where alternatemeans of compliance with “see-and-avoid”rules are employed); and

Occasional use of novel and exotic mate-rials for propulsion or aircraft recovery,meaning accident sites involving sys-tems where such materials are presentmay be unexpectedly hazardous to bothfirst responders and air safety investiga-tors alike.

The types of accidents and incidents most likely toresult from these differences are:

Midair collisions (unmanned/manned or un-manned/unmanned);

Loss of aircraft control in flight;

Fatalities/injuries on the ground uponground impact (inability to select point ofimpact);

Property damage on the ground uponground impact or collision with obstruction(inability to avoid surface-based feature orto select point of impact);

• Loss of safe separation between an un-manned aircraft and another aircraft;

Loss of aircraft control during ground move-ment; and

Post-crash injury or illness at the accidentscene.

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The Unmanned Aircraft System (UAS) Handbookand Accident/Incident Investigation Guidelineshave been in development for six years. Theystarted with the formation of the ISASI UnmannedAircraft Systems (UAS) Working Group (WG) atthe 2008 Annual Seminar in Halifax, Nova Scotia.Although initial interest was strong, the slow,drawn-out progress of regulatory activity on UASoperations seemed to have a somewhat chilling ef-fect on participation and collaboration under theUAS WG banner.

The effort was re-booted at the 2011 AnnualSeminar in Salt Lake City, Utah, and was built up-on the following year at the 2012 Annual Seminarin Baltimore, Maryland. A core group of reliable,engaged participants emerged. However, althoughthe assembly of reference materials moved steadilyforward, getting pen to paper for the UAS Hand-book and Accident/Incident Investigation Guide-lines themselves remained a challenge.

Ultimately, this first edition of the ISASI Un-manned Aircraft System Handbook and Accident/Incident Investigation Guidelines, hereafter calledUAS Investigation Guidelines, was primarily theproduct of a single author, supported by commentsand edits from core WG members and a few non-ISASI advisors. As such, it may suffer from thelimitations of a single author’s perspective, alt-hough significant efforts were made to avoid a too-narrow view of the world of unmanned aviation.To that end, it retains some content which was sug-gested for removal by various individual reviewers.Although at one point the philosophy “when indoubt, take it out” was advanced in support of thepared-down perspective, the reason for decidingotherwise was simple.

Many aspects of unmanned aviation policy-making, including basic questions regarding pilotand system certification, continue to evolve. Someissues remain controversial. As such, both appar-ent positives and potential negatives associatedwith properties of, or operations associated withunmanned aviation require as broad and public aconversation as possible. At the same time thetougher challenge – to overcome personal biasesand remain as objective as possible, regardless ofthe aspect of unmanned aviation being discussed –was taken seriously. Hopefully, this first effort hasemerged as judgment-free as possible.

It also should be noted that some content was

included simply as an introduction to the nature ofunmanned aircraft systems as a whole. Many par-ticipants in the WG process had limited or no expe-rience in investigating UAS accidents, or even withUAS operations as they are currently conducted.This is to be expected given the newness of thefield. However, it also showed that the UAS Inves-tigation Guidelines themselves needed to provide ageneral starting point for those new to the subject,rather than strictly adhering to a step-by-step pre-scriptive approach to UAS investigations.

In the years ahead, significant changes in think-ing about how and where to fly UAS are likely tooccur, and some such changes are likely to be driv-en by UAS-involved accidents. For now, however,there is a great deal of improvisation, as well as nosmall amount of political involvement in the devel-opment of rules regarding UAS operations from oneState to the next. These UAS Investigation Guide-lines are intended to highlight where risk exists, aswell as how and why that risk has been accepted asthe unmanned aviation sector evolves into a stableelement of the overall aviation system.

The UAS Investigation Guidelines also had to besweeping enough to explain why all unmanned air-craft systems are not created equal. Apart from (1)not being capable of conforming to the “see-and-avoid” concept as it presently is applied, and (2)relying upon a continuous electronic connection be-tween an unmanned aircraft and its pilot in com-mand, unmanned aircraft may bear as little resem-blance to each other as an Airbus A380 does to anultralight. The tendency is to treat them as a unityfor regulatory purposes, or to simplify their classifi-cation by reference to their physical properties anddimensions. This can result in either too much ortoo little safety-related rulemaking, as well as los-ing important distinctions between the capabilitiesof different types of UAS.

Supporters of efforts to enable “integrated” UASoperations side by side with those of manned air-craft need to understand the extent to which theformer can conform to existing requirements gov-erning the latter. For example, there is a growingpossibility that the “instrument flight rules/visualflight rules” paradigm will be challenged by theneed to accommodate certain limitations of, or de-sired applications for, unmanned aircraft systems.Similarly, the current system of separate classes ofcontrolled and uncontrolled airspace is increasingly

FOREWARD

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likely to be influenced by commercial pressure toenable access to virtually all of them by unmannedaircraft not equipped for flight in complex airspace.

The growing practice of granting exceptions tocurrent regulatory requirements simply because agiven type of unmanned aircraft is larger, smaller,or intended to be flown well clear of manned air-craft is likely to be confronted at some point by un-intended and unexpected interactions. The evi-dence already exists to show that such interactionscan and do occur; air safety investigations maywind up providing the necessary impetus to re-spond to them.

Finally, some States are being challenged re-garding the extent to which they should be regulat-ing unmanned aviation at all. When a “small un-manned aircraft” is indistinguishable from a“model aircraft” but for the intent of the pilot flyingit, the difficulty in crafting equitable and effectiverules for the safety of all affected by such opera-tions becomes obvious. However, a variety of resid-ual issues still have yet to be resolved.For example: Where and how are lines to be drawn – by alti-

tude segregation, by aircraft size or speed, or byother means?

Is something flown at an altitude below thatused by most other aircraft being operated“safely?” If not, whose responsibility is it totake action against the operator – national civilaviation authorities or local governments?

Air safety investigators must understand thesedebates as they expand and mature. We must beprepared to document the extent to which their res-olution succeeds – and fails – in the course of fu-ture investigations if we as a community are to pre-vent the recurrence of future unmanned aircraftaccidents as we have for past and present accidentsinvolving manned aviation.

In closing, some editorial notes seem in order toput the shape and content of this product in con-text. As noted above, during early reviews therewere disagreements among WG participants re-garding what it should include and what should beomitted. Some participants felt there was toomuch; some held that there wasn’t enough. Somefelt it wasn’t prescriptive enough, while others heldit was too prescriptive and tried to “set investiga-tive priorities.” For a document with no regulatoryidentity or authority of any type, neither argumentseemed particularly persuasive. This product isinformational only.

There are a host of matters that have yet to bedealt with adequately in the context of UAS opera-

tions themselves, such as the determination of in-flight conditions, maintaining clearance fromclouds, weather avoidance, and the potential haz-ards of GPS-derived versus barometric altimetry.The UAS Investigation Guidelines were created toserve as an atlas to the many subjects touched up-on by unmanned aviation, but they are not theproper place for exploring as yet uncharted terrain.

There was a sense on the part of some that everyreference to “accidents” should be amended to em-brace “accidents and incidents” (without referenceto “unusual occurrences” or other lesser-consequence events), or that the U.S. military dis-tinction between “accident” and “safety” investiga-tions should be reflected in the civil-oriented UASInvestigation Guidelines. There also were com-ments to the effect that more detailed training ma-terial or examples of previous UAS-involved acci-dents and recommendations should be provided,while others felt the UAS Investigation Guidelinesas a whole already might be straying into a regimemore properly addressed by the ISASI groups dedi-cated to training development or government ASIactivities.

These debates were difficult to adjudicate, inpart because fully addressing all of them likelywould have further delayed the release of this doc-ument by a year or more. Ultimately, the philoso-phy that “perfect is the enemy of ‘good enough’”held sway. With the delivery of this first effort, theUAS Working Group is ready to step aside to letother ISASI member-run groups take the raw ma-terial provided and mold it into tools specificallygeared to the needs of their respectiveconstituencies.

Readers are urged to use the list of references inAppendix 3 as a starting point for independent re-search, and to realize that there never will be a“last word” on the safety of unmanned aircraft sys-tems… just as there never will be in the broaderarena of aviation itself.

Thanks to all members of the ISASI UAS Work-ing Group who unselfishly gave of their time andwho with great deliberation produced the essenceof this Unmanned Aircraft System Handbook andAccident/Incident Investigation Guidelines. Mem-bers of the Working Group and others who provid-ed technical guidance are: Thomas A. Farrier, WGChairman; Mike Cumbie, MO5142; John Darbo,MO4218; Darren Gaines, MO3918; Doug Hughes,MO4415; Justin Jaussi, MO6105; Roy Liggett,MO5452; John Stoop, FO4873; and Al Weaver,MO4465. Technical Advisors: Adam Cybanski, Ca-nadian Forces; and Beverley Harvey, TSB Canada.

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PREFACE

There is growing awareness in the air safety inves-tigator (ASI) community that there are fundamen-tal differences between manned and unmannedaircraft, and that those differences need to be fullyunderstood when planning for and carrying outaccident investigations involving the latter. Theurgency with which the differences need to be ad-dressed will vary widely from one State to thenext. However, controlling many of the risks asso-ciated with unmanned aircraft system (UAS)1 op-erations is best accomplished as part of the regula-tory process that allows them in the first place.

Since the primary reason air safety investiga-tions are conducted is to prevent future accidents,civil aviation regulators and national aviation in-vestigative authorities need to begin dialogue onunmanned aviation issues sooner rather than lat-er. To be proactive in preventing UAS-related ac-cidents, ASIs need to help regulators apply lessonslearned from manned aircraft accidents to theemerging issues associated with unmanned air-craft operations. There is no point to repeating thesafety evolution of the present-day aviation envi-ronment with a new generation of foreseeable UAS

-related accidents.Based on the above, it appears there are two

key challenges facing the ASI community with re-spect to unmanned aviation: Being ready to conduct future accident investi-

gations involving unmanned aircraft systemswith procedures and capabilities that take intoaccount the differences they bring to the avia-tion environment; and

Making sure safety lessons written in bloodfrom previous accident investigations staylearned.These UAS Investigation Guidelines are in-

tended for use by a wide range of ASI audiences.The publication’s purpose is solely to introducereaders to major issues associated with the emer-gence of the UAS sector in the context of air safetyinvestigation requirements and challenges. Anyspecific capabilities or limitations of UAS de-scribed throughout the UAS Investigation Guide-lines are for illustrative purposes only. In particu-lar, it is understood that the rapid development ofUAS technology may overtake some of the UASInvestigation Guidelines’ content.

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The Unmanned Aircraft System (UAS) Inves-tigation Guidelines were developed by the In-ternational Society of Air Safety Investigators(ISASI) Unmanned Aircraft Systems (UAS)Working Group (WG). The ISASI UAS WGTerms of Reference directed participants toseek to accomplish the following tasks:1. Determine properties of unmanned air-

craft systems and their operations thatdiffer from existing aircraft.

2. Identify additional investigative capabili-ties that may need to be developed ormade more robust to support the investi-gation of UAS-involved accidents.

3. For Annex 13 to the Convention on Interna-tional Civil Aviation, Aircraft Accident andIncident Investigation:a. Determine the extent to which Annex 13

definitions for the States of Design, Man-ufacture, Occurrence, Registry and theOperator can be applied to unmanned air-craft systems, including their ground- andsatellite-based components.

b. Assess the adequacy of current guidance

regarding determination of the State re-sponsible for conducting the investigationof a UAS accident.

c. Document any need to recommend chang-es to Annex 13 related to the above.

4. Identify a standard dataset that should becaptured for each UAS-involved accident.

5. Identify additional UAS-specific trainingrequirements for air safety investigatorsbased on the above.2

6. Identify additional regulations that may beneeded to create or preserve evidence relevantto UAS accidents.

7. Make recommendations to the ISASICouncil regarding the best means of ad-dressing the above to other ISASI Com-mittees and Working Groups for appro-priate action.

* * * * *

The remaining chapters of this document individ-ually address, as appropriate, each of the sevenmain tasks.

CHAPTER 1Purpose and Structure of the UAS Investigation Guidelines

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CHAPTER 2Differences between Manned and Unmanned Aircraft

IntroductionThe definition of what constitutes an “unmannedaircraft,” “unmanned aircraft system,” “remotelypiloted aircraft,” “remotely piloted aircraft system,”and similar terms associated with unmanned avia-tion varies widely from State to State. Similarly,the circumstances under which any such aircraft orsystem is considered to have been involved in aninvestigation-worthy accident, incident or unusualoccurrence must be individually established basedon the associated regulatory structure and opera-tional environment.

For example, in 2010 the U.S. National Trans-portation Safety Board modified its Title 49 rulesto include the following:

Unmanned aircraft accident means an occur-rence associated with the operation of any public orcivil unmanned aircraft system that takes placebetween the time that the system is activated withthe purpose of flight and the time that the systemis deactivated at the conclusion of its mission, inwhich:

(1) Any person suffers death or serious injury; or(2) The aircraft has a maximum gross takeoff

weight of 300 pounds or greater and sustains sub-stantial damage.

In 2012, the Congress of the United States en-acted Public Law 112-95, the FAA Modernizationand Reform Act of 2012, which contained the fol-lowing definitions:

Section 331:The term “unmanned aircraft” means an air-

craft that is operated without the possibility of di-rect human intervention from within or on the air-craft.

The term “unmanned aircraft system” means anunmanned aircraft and associated elements(including communication links and the compo-nents that control the unmanned aircraft) that arerequired for the pilot in command to operate safelyand efficiently in the national airspace system.

The term “small unmanned aircraft” means anunmanned aircraft weighing less than 55 pounds.

Section 336:“Model aircraft means an unmanned aircraft

that is—(1) capable of sustained flight in the atmos-

phere;

(2) flown within visual line of sight of the personoperating the aircraft; and

(3) flown for hobby or recreational purposes.Based on the above, it is clear that the first pri-

ority of any air safety investigator faced with theprospect of inquiring into any occurrence involvingan unmanned aircraft of any size or type is to un-derstand the regulatory structure governing UASoperations. Once their authority and obligation toinvestigate are clearly established, air safety inves-tigators need to recognize that the similarities be-tween manned and unmanned aircraft far outnum-ber their differences.

At the same time, the similarities relied upon toassert the rights of unmanned aircraft to fly side byside with manned aircraft in shared airspace maynot outweigh their differences with respect to theirreadiness to operate under the same set of rules asother aircraft. History has proven that placing air-craft operating under different rules in shared air-space will result in accidents.

While the path taken from one State to the nextmay vary, concerns for the safety of the generalpublic typically arise whenever aircraft of un-known or unproven reliability are operated over-head. For UAS at the smaller end of the size spec-trum, there are some indications that civil aviationauthorities may be willing to accept a certainamount of risk on behalf of the public in exchangefor sustaining the growth of the sector as a whole.However, from a narrower perspective, the princi-pal safety issue that always must be considered isthe ability of aircraft operators to interact safelywith other operators within the existing aviationsystem, regardless of how their aircraft are de-signed, operated, or certified.

In exploring these matters further, civil aviationauthorities and national investigative entities willfind it useful to develop a working understandingof the nature of the differences among unmannedaircraft systems, as well as those between mannedand unmanned aircraft in general, and how thosedifferences affect the regulation, operation andrisks associated with specific unmanned aircraftflown in specific environments. At the same time,all parties should be clear that the mere fact thatan aircraft involved in an accident is unmanned isnot evidence that all such aircraft are unsafe.Likewise, the fact that an unmanned aircraft is in-volved in an accident should not automatically be-

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come the central feature of the ensuing accidentinvestigation unless and until its differences areproven relevant to the inquiry.

With the above caveats firmly in mind, it isequally important to acknowledge that while thetypes and consequences of accidents involving un-manned aircraft systems may be indistinguishablefrom those involving manned aircraft, the underly-ing cause or causes of such accidents may be quitedifferent. As such, unmanned aircraft accidentsmay lead investigators to make very different rec-ommendations for future prevention than would bethe case for manned aircraft accidents occurringunder similar circumstances.

Also, the possibility always is present that sometypes of accidents largely controlled by previouspreventive actions could reassert themselves in theunmanned sector. The nature of unmanned air-

craft systems and the limitations they impose upontheir pilots – such as the inability to assess flightconditions beyond whatever data on them has beenprovided for in the system’s design – may preventpreviously developed preventive strategies or sys-tems from operating as effectively as they normallydo for manned aircraft. Such effects may not beobserved for some time, especially if unmanned air-craft operations are relatively infrequent and typi-cally receive special handling.

Key Concepts Underlying UnmannedAircraft Systems

In 2007, RTCA Special Committee 203 first offeredan information architecture diagram (Figure 1)that shows the requirements for an unmanned air-craft system at a glance:

Note that the three principal nodes depictedabove – the unmanned aircraft, the ground controlstation (GCS), and the airspace within which theyoperate – always are present, no matter if one isreferring to a hand-launched aircraft of thirtyminutes’ endurance or a jet-powered, interconti-nental-capable high altitude aircraft. This is oneof the main reasons why this diagram is so power-ful when used to examine both the conceptual ba-sis and the implications of unmanned aviation.

Most UAS operators assert a desire to move to-ward a system state where unmanned aircraft areallowed access to non-segregated airspace on a “fileand fly” basis and are handled the same asmanned aircraft. This notional end state should beconsidered a point of departure for exploring theextent to which unmanned aircraft systems – ei-ther in general or where individual systems lackcertain capabilities required of manned aircraft –are capable of achieving side-by- side participationin shared airspace, and which should be a topic ofdiscussion in any accident sequence where bothmanned and unmanned aircraft are involved.

For the foreseeable future, unmanned aviationis best conceptualized as “unoccupied aircraft pi-loted from physically separate ground control sta-tions.” Active piloting, where a single responsiblepilot in command is required to exercise one-to-onesupervision over the operation of a single un-manned aircraft as a “human in the loop” (HITL)or a “human on the loop” (HOTL), is crucial to anunmanned aircraft’s safe participation in the exist-ing aviation system.

Finally, it is important to acknowledge thatthere is no regulatory structure within which au-tonomous flight can be carried out safely, at leastin the United States, because manned aircraftare at liberty to fly anywhere that unmanned air-craft can outside special use airspace. This hasincreased interest in some circles for establishingsegregated airspace for the exclusive use of un-manned aircraft, even as other members of theunmanned sector continue to insist on unfetteredaccess to the system as a whole.

Key Differences between Manned andUnmanned AircraftFor the purpose of these UAS Investigation Guide-lines, the following should be considered the key

Figure 1. Common Components of an Un-manned Aircraft System (from DO-304, Guid-ance Material and Considerations for Un-manned Aircraft Systems (March 22, 2007))

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operational and physical differences betweenmanned and unmanned aircraft: The lack of a pilot aboard the unmanned air-

craft, meaning the aircraft’s condition, position,trajectory, and surrounding airspace cannot bedirectly perceived by its pilot in command(PIC).

Reliance on radio-frequency (RF) spectrum andcontinuous connectivity between ground controlstation(s) and aircraft for safe operation, includ-ing as a substitute for the PIC’s limitations de-scribed above; this has two potentialconsequences: A UAS pilot’s control over their aircraft issubject to disruptions not experienced inmanned aircraft; and There can be delays in both communicationsbetween the pilot and air traffic control and inthe pilot’s control inputs being received andexecuted by the aircraft;

The varying and sometimes extremely limitedabilities different types of unmanned aircrafthave to separate themselves from other air-craft (meaning operation under “visual flightrules” as currently constituted is not alwayspossible where alternate means of compliancewith “see-and-avoid” rules are employed); and

Occasional use of novel and exotic materials forpropulsion or aircraft recovery, meaning acci-dent sites involving systems where such mate-rials are present may be unexpectedly hazard-ous to both first responders and air safety in-vestigators alike.

The types of accidents and incidents mostlikely to result from these differences are: Midair collisions (unmanned/manned or un-

manned/unmanned); Loss of aircraft control in flight; Fatalities/injuries on the ground upon ground

impact (inability to select point of impact); Property damage on the ground upon ground

impact or collision with obstruction (inabilityto avoid surface-based feature or to selectpoint of impact);

Loss of safe separation between an unmannedaircraft and another aircraft;

Loss of aircraft control during ground move-ment; and

Post-crash injury/illness at an accident scene.In addition, the reliance of UAS on electronic

connectivity between aircraft and pilot means thefailure of the command and control link can have avariety of outcomes depending on: The type of UAS involved (and thus the amount

of system degradation to be expected followingsuch a failure);

The sophistication of on-board systems associ-ated with both post-loss behavior and the abil-ity of sensors aboard the aircraft to enable de-tection and avoidance of conflicting traffic;

The familiarity of the responsible air trafficcontroller with the management ofUAS- related emergencies; and

The volume of airspace within which unex-pected maneuvers can be accommodated safely.

Finally, one of the immediately obvious differ-ences between manned and unmanned aircraft –and among different types of unmanned aircraft –is the enormous range of sizes to which unmannedaircraft are being built. Estimates vary widely asto the proportion of large versus small unmannedaircraft that eventually will constitute the globalmarket. However, it is safe to say that the econom-ic advantages of those at the smaller end of the sizespectrum are likely to make them far more popular,and in far wider use, than their larger brethren.

The mass and performance of any aircraft hasobvious implications regarding the amount of risk agiven system or operation might entail. However,for the purposes of air safety investigations, theseattributes are most worthy of consideration in thecontext of the amount of damage a given unmannedaircraft might be expected to inflict on another air-craft or on people or property it collides with on theground.

At the same time, it is important to rememberthat some equipage and/or capabilities normallyexpected of aircraft in a given class of airspace maybe impractical to install in smaller unmanned air-craft with limited range, payload or on-board elec-trical power. This possibility should be exploredany time a small-size UA is part of any accidentsequence in complex or congested airspace.

The above should be taken into considerationin determining the scope and level of effort thatmay be required for any investigation involving anunmanned aircraft system. While none may proveto be relevant to a given accident sequence or af-termath, all represent potential complicationsthat must be understood fully in order to includeor exclude them from detailed consideration, andthat may drive the need for additional investiga-tive resources – at least on a temporary basis –beyond those normally required for manned air-craft accidents and incidents.

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Special Aspects of Unmanned AircraftSystem Differences

“Detect and Avoid” Systems-Detect and avoid(DAA) systems, sometimes referred to as “senseand avoid” or “detect, sense and avoid” systems,are still largely in their infancy. Although somecommentators try to equate DAA with existingflight path surveillance and warning capabilitieslike traffic alert and warning systems (TAWS),DAA represents a significantly more complex set ofcooperative and interrelated technologies.

The simplest way to think of a high-functioning DAA system is to understandthat it must in very rapid and continuoussuccession: Detect electronic signals from aircraft

equipped with transponders, Mode S“squitters” or Automatic Dependent Surveil-lance – Broadcast (ADS-B);

Detect non-emitting aircraft or surface-basedobstacles that would be visible to the nakedeye (e.g., gliders, vintage aircraft, balloons,buildings, antennas);

Process all such targets through an algorithmthat allows for performance differences amongthe various types of aircraft that could be en-countered or the maneuvering required toavoid a fixed obstruction;

Command the unmanned aircraft or its pilotto maneuver in such a way as to remain wellclear of the conflict; and

Annunciate any course, airspeed or altitudechange to the pilot or directly advise the ap-propriate controlling agency that it has exe-cuted an autonomous avoidance maneuverthat has it off its assigned heading or altitude

An additional property of DAA systems as cur-rently envisioned is that they most likely will in-corporate two distinct sets of behaviors. The firstresponse to encounter detection will be for thesystem to maneuver the aircraft – or to provideguidance to the pilot supporting such maneuver-ing – so as to remain “well clear” of conflictingtraffic or obstacles (a subjective term requiring anas-yet undetermined objective threshold). Suchautonomous or directed maneuvering ideally willbe carried out without violating an air traffic con-trol clearance or other regulatory requirementssuch as altitude, proximity to congested areas,etc.

The second response will become controllingshould a conflict progress to the point where more“TCAS-like” response is needed, and would be in-

tended to prevent an imminent collision. Thisfunctionality is more likely to be automated, bothto avoid latency issues (see Chapter 3) and becausea UAS pilot would have no way of gauging the ac-tual proximity of the other aircraft or the preciseavoidance maneuver needed that would ensuresafe separation while not exceeding the unmannedaircraft’s flight envelope.

Various technical solutions for DAA chal-lenges are being explored, including sensorcombinations that fuse visible or infrared im-agery with electronic detection equipment. Itis unlikely that an industry-level standard,incorporating all of the capabilities describedabove while imparting an acceptable weightand electrical power penalty, will be in placefor the foreseeable future. However, work isproceeding to this end, with RTCA SpecialCommittee 228 having established a workinggroup specifically directed toward this effort.

The complexity of DAA architecture and sys-tem logic alone is not the only reason why special-ist knowledge most likely will be required to ex-plore a given collision scenario. For the nearterm, the larger problem is that government- ap-proved performance standards and specificationsfor DAA systems themselves do not yet exist. Atthe same time, pressure to move forward with ef-forts to integrate manned and unmanned aircraftoperations in shared airspace is likely to driveregulators’ acceptance of DAA systems that aredeemed capable of reducing the risk to other air-craft and to the public, but which are based onproprietary or otherwise non-certified criteria.

Finally, it is worth noting that many observersconsider DAA systems to have the potential to beinherently superior to human vision in the “see-and-avoid” role. Human perception is limited oradversely affected by any number of conditions,both from an anatomical and an “attention” per-spective.* A continuously scanning DAA systemnever would be looking the wrong way, distractedor otherwise taken away from its designed pur-pose. When any conflict enters the detectionthreshold, such a system will warn of or react to itas appropriate.

By the same token, the likely pace of DAA evo-lution versus demand for expanded UAS opera-tions most likely will result in tremendous varia-bility among DAA installations. This in turn willmean investigative authorities will need to haveaccess to subject matter experts who can evaluatethe effectiveness of individual DAA solutions that

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may come into question as a result of an aviationaccident or incident.

Cockpit Design-While the subject of cockpitdesign may be considered largely in the domain of ahuman factors investigation (see Chapter 3), thecontext of an aircraft accident investigation puts asomewhat different perspective on the issues thatmay arise where unmanned aircraft systems areinvolved.

The “cockpit” of an unmanned aircraft is aground control station not physically attached tothe aircraft in any way. Its complexity and sophis-tication may be indistinguishable from that of anairliner’s flight deck, or it could be as simple as ahand-held control box identical to one used to con-trol model aircraft. In any event, except for a fewinstances where military operators are attemptingto move toward some type of “common cockpit” ca-pable of being configured to fly a variety of differentUAS, it is highly unlikely that the human-machineinterface (HMI) in use has been developed withmuch attention to existing cockpit/flight deck de-sign requirements or the requirements of flight inthe existing aviation system.

While this may seem counterintuitive, manyUAS designs were brought into service through ac-celerated procurement processes (e.g., the“Advanced Technology Concept Develop-ment” (ACTD) initiatives) on an urgent basis. Be-cause they were intended for use during armed con-flict but would be incapable of defending them-selves from aerial engagement, their developmentwas conditioned by an implied assumption thatthere would be little or no competing use of the air-space within which the unmanned aircraft wereintended to operate.

The procurement strategy for some early medi-um and high altitude long endurance UAS alsoplaced an emphasis on maximizing the likelihoodof efficient, successful mission accomplishment.While the solutions to certain challenges (e.g., con-trol redundancy, payload operations, etc.) were nov-el and elegant from an engineering perspective,they did not always take into consideration pilotworkload, usage and task prioritization issues rou-tinely accounted for in the design of certificatedmanned aircraft and addressed through formal sys-tem safety programs.

A well-documented example of the kinds of prob-lems resulting from these trade-offs is that of aU.S. Customs and Border Protection Predator Bthat crashed in Arizona in 2006. The aircraft wason patrol along the southern U.S. border when itexperienced a “rack lock-up” that disabled the

pilot’s controls. He switched over to the sensor op-erator’s position – which was equipped with identi-cal controls – only to see the aircraft immediatelybegin to lose altitude. He was unable to regain con-trol, and the aircraft crashed.

Among the multiple issues uncovered in thecourse of the investigation was the discovery thatproper use of the appropriate checklist would haveprevented the loss; the sensor operator’s consolewas not properly set up to assume control of theaircraft when the switchover was made. However,the HMI aspect of this is that controls normallyused by the pilot have a separate, alternate usewhen running the payload sensors, virtually guar-anteeing that a breakdown in checklist disciplinewould have a catastrophic outcome at some pointduring the system’s life cycle. Fortunately, in thiscase the hidden trap was discovered without loss oflife and has been addressed to some extent by sub-sequent design and training fixes.

The point of this discussion is that the potentialinvolvement of cockpit layout and “switchology” is-sues involvement in an unmanned aircraft accidentinvestigation is not necessarily a matter for humanfactors specialists alone. Rather, investigators willneed to be trained to explore how the system as awhole is routinely operated, any previously encoun-tered design issues reported by its users, and howmisleading, incomplete or inappropriate design fea-tures or informational cues can have unexpected orconfusing outcomes. Exploring these matters is nota human factors engineering or human perfor-mance line of inquiry so much as an operations lineof inquiry that will require specialist knowledge toeffectively pursue.

Accidents Where UAS Differences fromManned Aircraft May Be a FactorMidair Collision-A midair collision involving anunmanned aircraft and a manned aircraft probablyis the most likely type of event that typically comesto mind when considering worst-case scenarios in-volving UAS operations in shared airspace.*

Determining how the two aircraft came into con-flict may require examining how their respectiveoperations were being conducted and what they en-tailed; the presence and effectiveness of rules andprocedures intended to separate manned and un-manned operations; the qualifications of the un-manned aircraft pilot (if different levels of certifica-tion are allowed by the State of Occurrence); andsimilar issues of airspace utilization and crew certi-fication. At some point the question of whether one

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Figure 2. Example Design Eye Reference Point Diagram (Transportation Safety Board ofCanada)

or both pilots had the ability to see and avoid (ordetect and avoid, as appropriate) the other prior toimpact is likely to arise. Once a given investigationturns to this issue, it is likely to become far morecomplex, and developing recommendations intend-ed to prevent the accident’s recurrence will becomemore challenging.

If a manned and unmanned aircraft are in-volved, traditional means of determining themanned aircraft pilot’s perspective first should beemployed. Investigators may wish to determine ifthe manned aircraft’s pilot could have seen the un-manned aircraft by examining the collision geome-try against possible impediments to cockpit visibil-ity, such as through use of a design eye referencepoint diagram like that shown in Figure 2.

Once the unmanned aircraft has been located onthis type of diagram (i.e., from the manned aircraftpilot’s point of view), investigators will need to takeinto consideration how the unmanned aircraftwould have appeared. Unmanned aircraft come inall shapes, sizes and colors, in some cases meaninga much smaller than usual target, perhaps withlittle contrast against the prevailing background,may have been presented to the manned pilot. Al-so, unmanned aircraft operate at a variety of air-speeds depending on their type, meaning a conflictcould have developed much more quickly than usu-al or, conversely, with so little relative movementas to make it virtually imperceptible. This part ofthe analysis should allow a determination to bemade as to whether the manned pilot reasonablycould have had the ability to see and avoid the

unmanned aircraft prior to impact.When the question turns to the unmanned air-

craft pilot’s ability to avoid the collision, it will benecessary to determine how (or if) the involved sys-tem compensates for the pilot’s inability to directlysee and avoid other aircraft. In some cases, civilaviation authorities may have made a deliberaterisk decision to accept such a limitation withoutfurther mitigation, or by relying purely on the UASpilot having direct visual contact with his/her air-craft at all times based on how and/or where theunmanned aircraft is intended to operate. Howev-er, it is also possible that active and/or passive“detect and avoid” systems may be in use as well.

In exploring a midair collision from an un-manned aircraft system perspective, it is importantto bear in mind that so-called “airborne sense andavoid” (ABSAA) systems that perform DAA func-tions are aircraft-based. While some concepts aresimilar to traffic alert and collision avoidance sys-tems (TCAS), detecting other aircraft and providingdirection to the pilot regarding the best avoidancemaneuver, most involve a fusion of active and pas-sive sensors supported by on-board logic that iden-tifies conflicts and automatically takes or directsaction to separate the unmanned aircraft fromthem.

If an unmanned aircraft that should have beencapable of avoiding a collision by virtue of ABSAAnevertheless is involved in a collision, investigatorswill be faced with a highly complex technical prob-lem. They will have to determine how the encoun-ter unfolded, including if:

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The conflicting traffic was capable of beingdetected by the available sensor suite;

The detection value was sufficient to triggerthe appropriate warning and/or autonomousresponse (if autonomous maneuvering is ena-bled in the installed DAA system); and

Whether the amount of time between detec-tion and avoidance maneuver (if any) waswithin design parameters, as well as whetherthose parameters were appropriate to the ge-ometry of the encounter.

These questions normally will require signifi-cant engineering and modeling and simula-tion expertise to address, most of which isnot within a typical ASI’s knowledge base.

In contrast to the above, “ground-based senseand avoid” (GBSAA) systems typically support sep-aration between manned and unmanned aircraftby maintaining surveillance over a defined portionof the sky using surface-based sensors, most com-monly using radar capable of seeing both tran-sponder-equipped and non-squawking aircraft.Three key issues most likely will need careful scru-tiny wherever a collision or loss of separation takesplace in a GBSAA-protected volume of airspace: Whether the system successfully detected the

conflict in a timely manner; Who and how the system warned of the con-

flict; and

Whether the UAS pilot’s response was appro-priate to the warning.

As with many aspects of UAS operations, thereare no settled specifications or performance stand-ards for GBSAA systems. Similarly, while thereare a number of innovative approaches to providingGBSAA services at various locations, there is noconsensus regarding the system architecture usedto enable them. Some concepts involve dedicatedradar systems, while others use existing air trafficcontrol radar where those systems have been eval-uated and deemed suitable based on their altitudecoverage, ability to effectively track non-cooperative targets, etc.

At the same time that investigation into thepoint-of-view and surveillance dimensions of theaccident sequence is undertaken, all recorded datacaptured by the involved UAS – including the“take” from any sensors oriented in the direction ofthe axis along which the collision took place –should be obtained for examination as well. Thiswill allow investigators to assess the extent towhich unmanned aircraft system crews typicallyrely on normal spectrum, low-light or infrared cam-eras to scan for conflicting traffic, as well as the

field of view offered by each such system.It may be procedurally acceptable or legally

conformant to use on-board sensors to support col-lision avoidance, or even as an alternate means ofcompliance with a State’s implementation of the“see and avoid” principle. However, it may be dif-ficult for investigators to determine the reasonable-ness of using such systems for clearing an un-manned aircraft’s flight path if doing so is consid-ered an approved technique. As such, close consul-tation with regulatory and certification authoritiesmay become necessary on that point.

Loss of Control Accidents (Airborne)-Unmanned aircraft, like their manned counter-parts, sometimes are involved in accidents wherethe pilot in command loses control of the aircraft.However, with unmanned aircraft, investigatingsuch accidents and incidents can be a more com-plex process simply because there are many moreways such a failure might occur. One’s traditionalmental image of an “out of control” aircraft must besupplemented to include another scenario altogeth-er, where an unmanned aircraft autonomously fliesitself to a final destination that may or may not beknown.

For investigations conducted under existingmodels and taxonomies, it is useful to distinguishbetween events involving the failure of the controland non-payload communications (CNPC) linkfrom those where the link is in operation but theaircraft becomes uncontrollable. In the formercase, the pilot may no longer be in or on the controlloop, but a reasonably sophisticated aircraft mayremain stable and navigate itself to a pre-determined point (following a “lost link profile”).Alternately, it may fail to revert to the prepro-grammed profile and instead take up an unknowntrajectory (“flyaway”).

In the latter case, for the purpose of this discus-sion, a UA loss of control takes place when the pilotis no longer able to change the aircraft’s heading,airspeed or altitude through an otherwise function-ing CNPC link. This type of malfunction typicallyis the result of a mechanical or structural failureaffecting the movement or condition of a primaryflight control or control surface, or due to a failurein the transmission of a control input or its trans-lation into a control input aboard the aircraft. Todate such failures have proven to be rare, but whenthey occur they are extremely difficult to diagnoseremotely.

For UAS accident and incident investigators, thegreatest virtues of just about every unmanned air-

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craft occurrence – and particularly in cases of lossof control resulting in the loss of an aircraft – are (1)having a live pilot to talk to, and (2) having thepossibility of obtaining significantly more perfor-mance data than is usually captured by a flight da-ta recorder readily available in the ground controlstation, at least where more complex UAS are in-volved.5 The pilot’s testimony can provide signifi-cant clues regarding the cause of virtually any kindof accident; rich recorded data can augment the pi-lot’s recall and understanding of the sequence ofevents and possibly provide clues as to any discon-nects between perception and reality where suchmight exist.

At the same time, as is the case with all UASaccidents – and especially those involving loss ofcontrol – it is vital to remember that a pilot’s abilityto provide information about the sequence of eventsis almost totally dependent on the extent to whichthe system itself provided that pilot with infor-mation, and that data provided to the ground con-trol station is totally dependent on a functioningdownlink throughout the period of interest.

Loss of Control Accidents (Ground) andGround Collisions-The possibility of a runawayunmanned aircraft on the ground is hardly withoutprecedent in manned aviation. Brake failures, air-craft getting away from their pilots after being“prop-started” and a host of other scenarios haveplayed out over time. Similarly, collisions withfixed obstacles or other aircraft regularly take placein manned aircraft operations and should be ex-pected in unmanned operations as well. In general,unmanned aircraft should be assumed to have thesame potential vulnerability to such mishaps astheir manned counterparts, and many such eventsare likely to be traceable to the same or similarcauses and precursors.

At the same time, differences between mannedand unmanned aircraft can have a bearing on thenature and outcomes of ground accidents involvingthe latter. For example, the failure of a CNPC linkduring ground operations can have unexpected ordifficult-to-avoid consequences, particularly if onetakes place in close proximity to other aircraft orsurface obstacles. Most unmanned aircraft incorpo-rate on-board logic that will immediately apply theaircraft’s brakes and/or shut down its engine imme-diately upon detecting a lost link.

Unmanned aircraft systems intended to be tax-ied to or from a takeoff or landing surface typicallyprovide their pilots with the means and a processfor doing so safely. UAS pilots may watch

marshallers with forward-looking optics, follow taxilines, and stop at hold-short lines, just as theywould from the cockpit of a manned aircraft. How-ever, investigators must bear in mind that, whilesuch operations may appear to be conducted in anidentical manner to those performed by mannedaircraft, UAS pilots operate under significant limi-tations with respect to their field of view.

System/Component Failure or Malfunction-Accident sequences that begin with component fail-ures or malfunctions can be particularly insidiousin unmanned aircraft simply because of the poten-tial delay in the pilot’s becoming aware of a devel-oping situation. Unlike manned aircraft, UAS pi-lots cannot directly perceive anything that mightcue them to a mechanical problem: no sounds, nosmells, no vibrations, no “control feel.” Virtuallyeverything they know about the condition of theiraircraft must be transmitted down through thesame limited amount of bandwidth that must beshared with critical flight performance and naviga-tion data.

As they gain experience with how operational orperformance issues show up in regular service,UAS manufacturers have become adept at identify-ing the relative criticality of different componentfailures or flight conditions. Since there are nostandards regarding what needs to be provided to aUAS pilot for situational awareness, each manufac-turer determines data requirements based on histo-ry, known system limitations and vulnerabilities,and available transmission and reception resources.

Investigators considering the possible role of asystem or component failure in an observed acci-dent sequence will need to familiarize themselveswith the specifics of the downlinked data providedto the UAS pilot. If it is concluded that the air-craft’s condition deteriorated in such a way thatwarning should have been provided prior to failure,the feasibility of implementing recommendationsregarding future instrumentation will be highly de-pendent on the demand such instrumentation willadd to the system in terms of weight, electricalpower or downlink requirements… not just the unitcost as might be the case with manned aircraft rec-ommended to receive a component repair or up-grade.

For unmanned aircraft, investigators also mustbear in mind that system or component failurescould entail malfunctions of the ground control sta-tion, not just the unmanned aircraft. A completelyairworthy, properly operating unmanned aircraftcan be lost if the ground control station supporting

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its operation becomes unusable or unreliable. Insome cases, GCS-related problems may appear tobe aircraft problems; if a second GCS or control po-sition is not available to take over the operation ina timely manner, an otherwise preventable acci-dent may occur. Once that has happened, it maybe difficult to diagnose the exact nature of the GCSproblem because uncertainty may remain regard-ing link stability, local interference, or other poten-tially distracting and irrelevant lines of inquiry.

Beyond the fundamental differences betweenmanned and unmanned aircraft cited to this point,other differences may present themselves in thecourse of a UAS systems investigation. In particu-lar, investigators may not assume that flight-critical components necessarily conform to stand-ards established for comparable components inmanned aircraft. Similarly, equipment subject totechnical standard orders or other means of guar-anteeing a specific level of performance or reliabil-ity aboard manned aircraft may be substituted forwith less stringently manufacturer or certified avi-onics aboard unmanned aircraft.

Until contentious issues of cost, airworthinesscertification authority and other “comparability”issues associated with integrating unmanned air-craft into shared airspace are resolved, investiga-tors must be prepared to encounter, document andanalyze the performance of on-board systems thatwould not be acceptable in manned aircraft in thecourse of accident and incident investigations.

CHAPTER 3Augmentation and Supplementation of

Existing Investigative Capabilities for UASInvestigations

Investigative Skills and KnowledgeAssociated with UAS Attributes

It is likely that specialized investigative skillswill be required to explore the involvement of oneor more of the above differences in a given accidentsequence or its aftermath. As may be expected,such skills will be needed to support analysis of theunique attributes listed above.

Human Factors—The human factors domain as itrelates to unmanned aviation must be consideredfrom two distinct perspectives: The extent to which an unmanned aircraft sys-

tem pilot in command is expected to be a “pilot,”with the body of knowledge and physical attrib-utes expected of those flying manned aircraft;

and The extent to which an unmanned aircraft’s pi-

lot can be reasonably expected to accuratelyperceive the flight environment and the imme-diate surroundings of his/her aircraft – in otherwords, to have appropriate situational aware-ness – when physically separate from thataircraft.

To the first point, at this writing there is insuffi-cient objective research available to allow air safetyinvestigators to make any independent judgmentsregarding how an unmanned aircraft system pilotshould be trained or certified. Such decisions areproperly the domain of the national aviation authori-ties who regulate unmanned aircraft system opera-tions. If the circumstances surrounding a given acci-dent under investigation suggest deficiencies inthese areas, appropriate findings and recommenda-tions should be made.

On the other hand, there is a large body of com-pelling historical information that points to how thesafe operation of aircraft is highly dependent on thepilot’s physical condition and fitness to fly. Again,each State that allows unmanned aircraft operationshas to make determinations regarding the specificstandards to which each pilot should be held. Thedistinctive nature of UAS operations includes notsubjecting the pilot to some of the more physicallychallenging aspects of flight, such as high physiologi-cal altitude or exposure to high Gs. In the sameway, some accommodations may be possible for cer-tain typical requirements, like normal color vision orsome physical impairments, simply based on howunmanned aircraft are flown.

This is not to say that some aspects of unmannedaircraft system operation do not place demands onthe physical or mental faculties of UAS pilots. Forexample, visual acuity is critically important for anyUAS operation where the pilot or a visual observermust keep the aircraft in sight to keep it clear of oth-er aircraft and obstacles. Similarly, being properlyrested is a necessary adjunct to any complex mentalactivity, as is good general health. Where a pilot’sfitness to fly or to carry out the responsibilities asso-ciated with flying might come into question in thecourse of an accident investigation, such issues cer-tainly will be worth exploring in the context of theexisting body of regulations applicable to the opera-tion.

The second perspective on human factors – howUAS pilots obtain and maintain situational aware-ness regarding the conduct of their operations – ismuch less clearly understood. One of the principallimitations under which such pilots must work is in

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having the vast majority of their situation(al)awareness regarding their aircraft’s operation, aswell as the condition of both the aircraft and theenvironmental conditions surrounding it, confinedto the visual sense. Further, the manner in whichmuch of the available data regarding these parame-ters is presented often requires interpretation; forexample, in some systems accumulating ice must bededuced by noting decreased performance, altitudeloss and similar symptoms rather than simply look-ing out a window and seeing ice.6

Throughout the first century of flight, aviationhuman factors experts made great progress in de-termining the best means of presenting informationto pilots, distinguishing between the different typesand criticality of flight-related information as wellas developing context-based rules for prioritizing it.Various types of displays have been developed tosimplify the identification of anomalous conditions,performance trends indicative of developing systemproblems, and differing severity of malfunctions.At the same time, there always has been at least animplicit understanding that direct perception of thesymptoms of some problems, such as unexplainedsounds, vibrations or smells, often supports theirdiagnosis or correction.

None of these cues are available to an unmannedaircraft pilot directly. A conscious decision must bemade by each UAS designer as to which infor-mation is important enough to warrant being addedto the limited data stream from aircraft to pilot.Even if it is deemed desirable to devote a certainamount of bandwidth to purely aircraft state data,developing digital surrogates for sensory-type infor-mation is relatively easily for some conditions (e.g.,identifying a rough ride through rapid excursionsin G-forces), but quite difficult for others (e.g., thesmell of an overheating electrical component, theaccumulation of smoke, etc.).

Another consideration is that the criticality ofsome flight conditions – such as turbulence or icing– varies widely from system to system. So, it is nota simple matter to standardize downlinked dataacross the entire constellation of unmanned aircraftsystems. This is especially the case where requir-ing unnecessary data to be transmitted and dis-played could result in pilot interpretation problems,information overload, a failure to provide data thatmight be more useful, or additional potentialsources of on-board malfunctions associated withthe information collection and transmission itself.

Following the above line of reasoning, it is notunreasonable to assume that at least some futureaccidents with UAS involvement may require the

commissioning of specific human factors studies toexplore investigators’ theories of potential accidentscenarios. This could include determining what apilot could have reasonably concluded about anemerging aircraft problem based on the informationavailable, what more could have been done to sup-port their situation awareness under given opera-tional conditions, or similar issues. Human factorsexpertise also may need to be applied to developingrecommendations to prevent future accidents aswell. This might entail addressing such issues asthe kinds of automation needed to support certaintypes of flight activity, automated functions mightneed to be made more visible to pilots to supportsituation or mode awareness, etc.

Finally, simply describing the constellation ofpossible human factors issues arising from un-manned aviation does little to ensure that the need-ed expertise will be available to explore them. Gov-ernments must take conscious steps as soon as pos-sible to support the growth of a qualified talent pooland an unmanned aviation-focused academic estab-lishment to deal with such challenges as they arise.While it might be ideal to have unmanned aviationhuman factors specialists embedded in each nation-al aviation authority, as a practical matter it wouldseem more useful to ensure that funding for the ac-ademic community is made available to develop ex-perts who could support both public and privateneeds for such skills.

Telecommunications—While telecommunicationsand frequency management expertise periodically iscalled upon in present-day aviation accident inves-tigations involving manned aircraft, it is likely tobecome far more prominent once unmanned air-craft become regular participants in the overall avi-ation system. One of the cornerstones of unmannedaircraft systems operation is the remote location ofthe pilot/operator. At a fundamental level, thismeans that the entire concept of unmanned avia-tion (other than where the aircraft are completelyautonomous) is dependent upon uninterrupted RF-based connectivity with adequate capacity for allneeded data to be exchanged without loss ordistortion.

Prior to the advent of widespread unmanned air-craft operations, the regulatory relationship be-tween aviation and telecommunications largely wassettled. Portions of the RF spectrum have longbeen reserved for aircraft voice communicationsand navigation equipment; whenever new require-ments for additional capabilities have emerged(e.g., Airphones, onboard WiFi, satellite communi-cations, controller-pilot data link communications),

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they have been aligned with the appropriate partsof existing allocations on the basis of how they op-erate, and accommodated at a regional or globallevel as needed.

However, it is important to note that in recentyears it has been rare for such new requirements tobe related to the safety of flight. Rather, they havebeen driven by the emergence of new technologiesintended to increase the efficiency of tasks alreadyconducted in aviation operations, or they have beencreated for the convenience of aircraft operators orpassengers. Unmanned aviation has raised thestakes in the relationship between those who regu-late flight and those who regulate resources sup-porting flight, since access to spectrum – and lots ofit – is a prerequisite to making use of unmannedaircraft safely and effectively. At the same time, un-manned aircraft move, meaning the frequencies usedto control cannot be allocated using the location-basedmodel applied to air traffic control or navigational aidfrequencies.

There are two distinct aspects of how the finiteresource of spectrum must be managed in order forunmanned aircraft to be operated safely, both ofwhich will require expert knowledge to interpret inthe event of an aviation accident in which the relia-bility, stability or adequacy of control-related linksmay be in question: the frequencies used, and thebandwidth required on each of those frequencies.To understand the distinction between the two, abrief explanation is in order.

In the earliest days of radio, it was easiest togenerate and broadcast signals of comparativelylong wavelengths (in the “low frequency” and“high frequency” bands). These signals also hadthe side benefit of covering very long distances byvirtue of their property of being reflected by theionosphere, “skipping” over the horizon. As peo-ple learned the relative advantages and disad-vantages of different types of transmissions at dif-ferent frequencies, it became obvious that some or-ganizational scheme would need to be imposed onall of the prospective users of the airwaves to pre-vent their mutual interference. To some extent, thephysics of electronic communications argued in fa-vor of assigning certain uses to specific frequencies.For the rest, however, competing applications vyingfor exclusive use of part of the spectrum often hadto be individually licensed on the basis ofavailability.

The responsibility for such assignments was firstworked out at the international level through anexisting communications-oriented body – the

“International Telegraph Union,” now the Interna-tional Telecommunications Union (ITU) – with in-dividual nations granted portions of the spectrumfor their respective exclusive use, and other por-tions protected to enable commonality for world-wide systems to operate, such as those dedicated toaeronautical activity. However, many current UASactivities share portions of the spectrum with otheroperations. Military UAS often operate on military-reserved frequencies. There also is a small portionof the spectrum set aside exclusively for short-range hobbyist/model aircraft use, which at least inthe U.S. is required to be entirely noncommercial.7

The vast majority of UAS command, control andcommunications most commonly are carried out inthe range of frequencies between 900 megahertz(MHz) and 30 gigahertz (GHz). There are three“services” under which aviation-specific spectrum isallocated by the ITU: Aeronautical mobile (route) service (AM(R)S); Aeronautical mobile satellite (route) service

(AMS(R)S); and Aeronautical navigation radio service (ARNS).

Allocations for UAS uses are complicated byneeding to be made from the first two of these, eachof which is separately administered. The reasonwhy different domains are involved becomes clearerby looking at Figure 3.

Figure 3. UAS communications segment spec-trum/bandwidth requirements by communi-cations node (from an issue paper preparedfor the World Radiocommunication Confer-ence 2007, Spectrum for UAS (Unmanned Air-craft Systems): Status of WRC-2007 prepara-tion and proposal for a new agenda item forWRC- 2011, Didier Petit and Alain Delrieu)

The ITU has identified three distinct types of“radiocommunications” required to operate an un-manned aircraft in controlled airspace: Radiocommunications in conjunction with air

traffic control relay;

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Radiocommunications for UA command andcontrol;

Radiocommunications in support of the senseand avoid function.8

In addition to the above, many UAS incorporatedata downlinked from apayload such as an on-board camera or other sen-sor, which may use an en-tirely different part of theRF spectrum but which, bythe nature of how its“take” is used, may also beflight- critical. To providefor all of these require-ments, unmanned aircraftsystems require significantamounts of bandwidth tosupport both uplinked anddownlinked data. Mostunmanned aircraft haveseparate downlinked datastreams – one for control,the other with the payload“take.”

Figure 3 shows that the remote location of thepilot and the need to downlink both control andpayload data from the aircraft drive requirementsfor different frequencies. The amount of data thateach frequency hosts requires significant spacefrom competing or potentially interfering signals,and, for security may utilize several separate fre-quencies among which the transmission can “hop.”Further, the vast majority of beyond line of sight(BLOS) UAS operations require satellite service(although some terrestrial methods are being ex-plored) for both data and voice support.

Previously, the UAS community has acknowl-edged the complexity of unmanned aviation and therelationship among its various components, but hastended to downplay the criticality of how those com-ponents must interact to assure their safe opera-tion. In response to the need to re- imagine thefunctional relationships between pilot and aircraft– and to graphically illustrate the different types ofdata exchanges that need to take place through thevarious links – RTCA Special Committee 228’sWorking Group 2 (WG2) reconsidered the originalarchitectural diagram shown in Figure 1.

The new “control chain” conceptual model now inuse by WG2 (Figure 4) differs from the originalRTCA DO-304 notion of “segments.” The groundcontrol station now is envisioned as the place wherehuman- machine interface takes place, and a new

hardware/software node is referred to as the“communication infrastructure.” This change ap-pears to have been made to enable the revised mod-el to accommodate varying levels of connection com-plexity, from radios to a ground-based data distri-

bution system that is envisioned to provide a“signal in space” from terrestrial stations to air-borne aircraft.

While the updated vision of UAS system logicdoubtless is helpful for engineers, it is somewhatdaunting for those new to unmanned aviation.However, WG2 also re-imagined how to portray thedifferent types of flight-required datalinks, which ishelpful in understand both the complexity of linksand how they are used. These demands drive sepa-rate but equally pressing bandwidth requirements.

What Figure 4 is intended to show is that thereare a number of data exchanges constantly occur-ring between a GCS and a UA, especially where aBLOS operation is in progress. SC-228 is not con-cerning itself with any requirements for spectrumthat may be needed to support payload data(although some types of UAS see payloads asproviding possible alternate means of compliancewith see-and-avoid requirements – a flight-criticalfunction).

Also, SC-228 appears to be confining its atten-tion to the far left side of the diagram, where onlythe telecommand (uplink) and telemetry (downlink)data supporting BLOS operations would be accord-ed “protected” bandwidth. Requirements for airtraffic control (ATC) communications presumablyare to be met through existing spectra, althoughhow this is to be assured has yet to be determined.

Figure 4. RTCA SC-228 WG2 “Taxonomy of UAS Data Links”

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* * * *Beyond the system complexity arising from the

multiple parts of the RF spectrum needed for UASoperations, the bureaucratic complexity describedabove suggests there could be a purely“management” aspect to UAS-related telecommuni-cations issues that may arise in the course of anaccident investigation.

Consider a scenario where a link became unusa-ble at a shorter range than should have been thecase, or was disrupted by interference due to aninappropriate or inadequate allocation of spectrumfor unmanned aviation operations. Delving into apossible accident sequence of that type, and thendeveloping meaningful recommendations to pre-vent its recurrence, requires specialist understand-ing of the properties of radio waves at different fre-quencies, the administration of available spectrum,the degrading effects of intentional or unintention-al interference, and the matching of available spec-trum with intended use as a function of suitabilityrather than its just being “open.”

Different governments (i.e., ICAO memberStates) are organized quite differently for regulato-ry purposes. ASIs need look no further than theirown domain to realize that the relationship be-tween their country and others in the aviation envi-ronment is to some extent conditioned by theirState’s participation in ICAO. A similar relation-ship typically exists between individual nationsand the ITU, which governs the allocation of spec-trum, maximum output power of transmitters, anda whole array of similarly vital aspects of RF appli-cations. Therefore, investigators need to act assoon as possible to identify points of contact in theappropriate agencies within their respective gov-ernments to be ready to address issues of the typedescribed in advance of an accident requiring theirmobilization.

Based on the foregoing discussion, the reasonswhy telecommunications expertise will be essentialto UAS-related air safety investigations should beapparent. However, as mentioned earlier in thissection, the reliance of UAS on their“communications segment” also brings with it twospecific concerns: the potential for its disruption(control link failure), and the practical implicationsof having a built-in lag in the communications be-tween pilot and controller and pilot and aircraft(latency).1. Control Link Failure Impacts

From a purely operational perspective, a fre-quently made analogy is that UAS control link

failure (i.e., a “lost link” occurrence) is pretty muchthe same as a failure of two-way radio communica-tions, even when it occurs in controlled airspace.Proponents of this line of reasoning rarely stepthrough the actual consequences; they simply as-sert that the two events’ impact on surroundingaircraft and the ATC system is equivalent, as is thecontroller’s response to them.

Unfortunately, such is not the case, at least forthe foreseeable future. A manned aircraft’s crewflying on an instrument flight plan follows theclearance issued to them, even if communicationsfail. From the clearance limit onward, there arewell-defined procedures regarding what the pilot isto do based on what he or she was told to expect,and nothing normally will prevent them from fol-lowing those procedures. They also can communi-cate their situation via transponder in most situa-tions, either by squawking 7600 or 7700 as appro-priate to their circumstances.9*

An unmanned aircraft system control link fail-ure cannot be described in terms of “standard pro-cedures” because each such failure may have acompletely unpredictable outcome, a highly specif-ic, well-defined outcome, or something in between.Such variability begins at the moment of link fail-ure: Was only the pilot’s ability to control the air-

craft affected, or were voice communicationswith ATC disrupted as well?

If the latter, how does air traffic control becomeaware of the aircraft’s degraded operationalstate? Is it programmed to change its tran-sponder squawk, will it do so immediately or isthere a built-in delay between the failure andthe initiation of any on-board programmed be-havior?

Was the unmanned aircraft programmed to pro-ceed to orbit at a known point (sometimes re-ferred to as a “flight termination point”) or re-turn to its point of origin in the event of controllink failure? Was the flight termination pointchanging throughout the flight? If so, wherewill the aircraft turn toward, and how longmight it be before it takes up a new heading,airspeed or altitude?

Assume that an unmanned aircraft is in BLOSoperation and any programmed delay between linkfailure and initiation of a “lost link profile” haselapsed. What will the aircraft do next? There is noway to answer this question without knowing thespecifics of the aircraft’s designed capabilities andthe specifics of its pre-programming.

Even if you know that it has been programmed

21

Figure 5. Differences between Manned and Unmanned Aircraft Transactions (ICAO Aeronau-tical Communications Panel Working Paper, ACP-WGF24/WP15, 21-25 March 2011)

to proceed to a particular point in space – say, inmilitary reserved airspace – and ATC is in contactwith the pilot, there is no way to determine precise-ly how the aircraft will navigate itself to that pointin space. This situation can be compounded in com-plexity by taking place outside radar surveillance;control link failures frequently are accompanied bydownlink failures, meaning the pilot in commandmay no longer be receiving positional or perfor-mance information from the aircraft and thus can-not advise air traffic controllers of its position.

The kinds of imponderables cited in this exam-ple are likely to persist for some time. The contentsof UAS flight plans and ATC progress strips willhave to evolve significantly to include critical infor-mation that allows controllers to anticipate thenext moves of an unmanned aircraft that unexpect-edly reverts to what is for all practical purposes anautonomous mode of operation.

In the interim, any investigation resulting froma control link failure will need to be augmented bypersonnel with an intimate understanding of theinvolved system’s architecture and post- failure

decision logic, and who do not have an institutionalstake in the investigation’s outcome. The potentialfor control link disruption is perhaps the singlegreatest common vulnerability across the entirespectrum of unmanned aviation, and the tolerabil-ity of this vulnerability has a direct bearing on theacceptability of the concept of unmanned aircraftsystems themselves.2. Latency Impacts-When air traffic controlcommunications first began being supported by sat-ellites, questions arose regarding the potential ef-fects of delays in control instructions being receivedand executed. The term “latency” came into use todescribe the lag time required for a given transmis-sion to be transmitted to a satellite in low Earth orgeosynchronous orbit and then re-transmitted to itsintended recipient.

The advent of unmanned aircraft systems

brought a new dimension to the latency issue in the

context of flight operations. A great deal of useful

research was conducted on the effects of communi-

cations latency when it first was introduced, and

22

much of it was captured for consideration by the

now-disbanded “Access 5” UAS study group.10

However, referring back to Figures 1 and 3 earlier

in these UAS Investigation Guidelines, it is clear

that long-distance telecommunications are needed

to support unmanned aircraft systems operations

both for communications and for aircraft control.

Thus, “latency” for unmanned aircraft has implica-

tions both for the timely reception of control in-

structions and for the subsequent execution of those

instructions.This issue has been considered at some length in

the ICAO environment. For example, at a March2011 meeting of the Aeronautical CommunicationsPanel (ACP), a presentation on UAS “availability,continuity and latency” suggested that the additionof the need for “non-payload” communications coulddrive the total time between when an instruction isissued and carried out (“transaction time”) to ex-ceed standards established by ICAO Document9869, Manual on Required Communications Perfor-mance (RCP).

The paper’s author concluded, “The UAS trans-action time to meet the overall RCP10 require-ments probably is insufficient to be met by a satel-lite system.” This is an extremely strong state-ment, but is based purely on engineering analysis.Nevertheless, it has yet to make any meaningfulimpact on the evolution of beyond line of sight un-manned aircraft systems, certification require-ments, or policies to date.

Figure 5 illustrates the problem graphically.Each step of the transaction for an unmanned air-craft responding to a control instruction takesmeasurable time due to latency, which must beadded to the total time necessary for the controllerto issue the instruction and the pilot to respond toit. The time involved is extremely small, but thespeed with which aircraft operate and conflicts de-velop makes any delays a matter of some concern.

Despite the relatively small amounts of time laginvolved, latency has been observed to have oneconcrete effect on beyond line of sight UAS opera-tions: unmanned aircraft landing attempts madevia satellite-based control links rarely succeed. Thedisconnect between instrument readings, visual in-formation relied upon for pilot orientation and con-trol inputs almost invariably result in the pilot be-ing well behind the aircraft, reacting to flight condi-tions that already have affected the aircraft in pitchor roll. This is one of the principal reasons behindongoing efforts to develop reliable autoland systemsfor high-value BLOS unmanned aircraft.

It has been suggested that latency challengesshould form the basis of new approaches to UASdevelopment, including possibly placing more deci-sion-making and control capability directly aboardunmanned aircraft themselves. The safety recordof unmanned aircraft, including those involved inaccidents where their control links have been com-promised, will provide support for or direction tosuch efforts, as will the outcomes of UAS-involvedaccidents. However, until unmanned aircraft arecapable of independent two-way communicationsvia natural language or datalink messages to con-trolling agencies, latency is likely to be a normaland unchanging aspect of BLOS UAS operations.

Security Impacts—One final telecommunicationsissue that may need to be explored in the context ofan unmanned aircraft-involved accident is the pos-sibility that a failure observed in the sequence ofevents was deliberately induced instead of acci-dentally encountered. In the past, where bomb-ings, hijackings or intentional crewmember actionshave been the cause of aircraft losses, evidence ofcriminal acts usually has been identified fairlyquickly, and the investigative responsibility andprocess has migrated from safety to law enforce-ment authorities.

In unmanned aviation, actions intended to dis-rupt the conduct or control of a flight may be muchharder to trace or prove. The control link itselfcould be attacked; alternately, Global PositioningSatellite (GPS) signals could be jammed ormeaconed (overridden by a stronger, apparentlyvalid but incorrect signal). Individual investigativeand civil aviation authorities will need to considerdeveloping their own criteria for exploring the pos-sibility of criminal activity in the course of an un-manned aircraft system-related aircraft accidentbased on their individual threat assessments andthe specific circumstances surrounding a givenevent.

To sum up, the telecommunications expertisenecessary, civil aviation and national investigativeauthorities need to be prepared to either developtheir own resources or identify sources of supportwith working knowledge of the following subjectareas: Availability/suitability of supporting ground-

based telecommunications architecture. Availability/degradation of satellite-based over-

the-horizon telecommunications. Availability/adequacy of allocated RF spectrum

in the vicinity of an unmanned aircraft acci-dent.

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Aircraft Structures—Investigators specializing instructures-related factors are likely to have a livelyset of challenges before them in any major accidentinvestigation involving an unmanned aircraft. Thefundamental issues likely to be on the table are: For any accident involving in-flight structural

failure of an unmanned aircraft: How was the aircraft constructed? To what standards was the airframe built?

For any accident involving a midair collisionbetween a manned and unmanned aircraft re-

sulting in the loss of the manned aircraft: What parts of the manned aircraft were

affected by the initial impact? With what force did the impact take place? What unmanned aircraft components

imparted the greatest part of that force?

What role, if any, did the size, mass, velocity,airframe pliability or general construction ofthe unmanned aircraft play in how impactforces were applied and distributed?

How much force was the manned aircraftdesigned to tolerate at the point of impact?

Are current manned aircraft designstandards adequate to withstand the type ofcollision observed in the accident sequence?

Are current unmanned aircraft design stand-ards adequate to ensure the frangibility of theairframe (where appropriate) in the event ofan impact with a manned aircraft or inhabitedstructure? 11

Most structures investigators and aeronauticalengineers have the necessary expertise to carry outa UAS-involved investigation. However, such in-vestigations may entail understanding how un-manned aircraft designers elected to solve certainchallenges absent both formal certification stand-ards and the need to protect human occupants.

Unmanned aircraft often incorporate design fea-tures that add robustness to certain componentsand forego it in others. As such, qualified investi-gators would be well served by having the oppor-tunity to visit and consult with unmanned aircraftmanufacturers in advance of an investigation,simply as a way of calibrating themselves to recog-nize the tradeoffs and weight-saving compromisesmade in the end items.

Electrical Propulsion Systems—Investigators spe-cializing in powerplant-related inquiries are likelyto need some grounding in the emerging types ofpropulsion systems used by many cutting-edge un-manned aircraft. It is common knowledge thatmany unmanned aircraft make use of non-aviation

certified conventional powerplants (e.g. snowmobileengines and other high-torque, lightweight de-signs). It is less well known that the emphasis inmany unmanned aircraft designs is on extreme en-durance, which has led to a host of innovative ap-proaches to generating and delivering electricalpower to propellers that are totally unfamiliar tomost of the aviation community.

Three basic approaches to electric drivetechnology and ancillary system support currentlyare being used or tested on unmanned aircraft:

1. Battery power. This is by far the mostcommon in small UAS applications. Significant re-search is being conducted in an effort to increasetheir power (to support the powering of on-boardsystems other than the motor) and capacity (to en-hance their range or loiter capability).

2. Solar power. Solar-powered unmannedaircraft, intended for long-duration operations athigh altitude, are being explored in increasingnumbers. Their large wingspans are well suited tothe installation of significant solar cell arrays ontheir upper surfaces.

3. Fuel cells. Fuel cell technology has grownsteadily in recent years, and the unmanned aircraftcommunity is exploring ways of leveraging its effi-ciency and relatively light weight against a wholerange of on-board electrical requirements.

Pre-Accident Hazard AssessmentsInvestigative authorities may wish to make a studyof the specific unmanned aircraft systems certifiedfor operation within their State or area of responsi-bility in advance of any accidents, simply to applysome of the thinking suggested above to the specificscenarios most likely to be encountered based onthe certificated systems in use and to anticipate thetypes of expertise that may be required under cer-tain scenarios. Line-of-sight signal propagation and transmit-

ter range limitations. Availability/usage of RF spectrum and sufficient

bandwidth in a location where control loss or

degradation was observed. Individual unmanned aircraft system reliance

on uplinked and downlinked data for control,situation awareness and two-way communica-tions.

To avoid unnecessary and time-consuming de-velopment of comprehensive hazard assessmentsand similar tools for identifying and quantifyingrisk, investigators should start by asking them-selves a simple question: “Would the worst credible

24

outcome of encountering this hazard with an un-manned aircraft be any different than it would ifthe involved aircraft was manned?” If not, investi-gators need not expend energy on an unmannedaircraft-specific investigation, and may instead pro-ceed with a regular investigation.

On the other hand, if one of the unique aspectsof unmanned aviation appears to have played somepart in the accident sequence, the responsible au-thorities would be well advised to fully commit toan in-depth investigation capable of quantifyingtheir exact involvement – as well as any means ofpreventing their recurrence – in detail.

Beyond the top-level, first-order differenceslisted above, there are many possible differences ina number of areas where the scope and level of ef-fort that may be required for an investigation in-volving an unmanned aircraft system, or special-ized investigative skills that may be required, couldvary widely from State to State and accident to ac-cident. Areas where the possibility of variability orspecial provisions may come into play include: Regulations –

Unmanned aircraft system certificationstandards UAS pilot (operator) certification standards UAS operating rules, including specific limi-tations for certain classes of airspace Aircraft categorization, especially where agiven unmanned aircraft may be operated re-motely or in a manned (optionally piloted) con-figuration

Propulsion system – Reciprocating engine (aviation versus non-

aviation-certified) Turboprop engine (aviation versus non-aviation-certified) Turbojet/turbofan engine (aviation versus non-aviation-certified)Electrical (battery, fuel cell, solar, hybrid)

Communications system – Pilot-in-command (PIC) to air traffic control(ATC) line-of-sight communications PIC to ATC passing through aircraft

PIC to ATC enabled by satellite Control link –

Line-of-sight (LOS) only Beyond PIC’s visual range (non-satellite) Beyond line of sight (BLOS)12

Special features – Flight termination/ballistic recovery systems Payloads capable of interfering with other on-board systems Payloads used to fulfill flight-critical funtions

(e.g., navigation, see-and-avoid, etc.)

Considerations for Investigations Involv-ing Beyond Line of Sight UAS OperationsWhen faced with the need to initiate an investiga-tion involving BLOS UAS operations, investigativeauthorities will need to make early decisions re-garding how their resources should be deployed.The on-scene investigation will remain a necessarycomponent of the overall inquiry. However, thecondition and proper operation of the ground con-trol station or stations in use at the time of the ac-cident, as well as the status of the satellite or net-work in use at the time of the occurrence, areequally important elements that must be estab-lished as quickly as possible.

A possible worst-case scenario might involve twoseparate ground control stations in different partsof the world attempting a transfer of operationalcontrol at the time of the occurrence. This wouldmean securing evidence and gathering testimony atas many as four different locations: The crash site; The two GCS sites; and

A satellite or network operations center.To date, satellite operators have had rela-

tively little direct involvement in accident investi-gations, generally serving to provide informationsupporting such inquiries rather than being thefocus of some aspect of the accident sequence itself.

Air safety investigators and regulators may wish toreach out to such service providers in advance of anaccident or incident investigation to ensure the ap-propriate operational, legal and personal relation-ships are in place in advance of need.

Investigation of Accidents Involving ModelAircraftFormal air safety investigations are not constitutedto investigate model aircraft accidents, and Annex13 is not applicable to them. However, at somepoint air safety investigators and investigative au-thorities may be confronted by a situation where a“model” aircraft – one identified by rule, manufac-ture or common practice as being intended for hob-by or recreational use only – is determined to havebeen involved in an aviation accident sequence ofevents.

The extent to which the involvement of a modelaircraft’s involvement could be a complication willvary greatly based on the specific legal and regula-tory distinctions made from one State to the next.This in turn means legal expertise, hobbyist

25

knowledge of model aircraft construction and oper-ations, and familiarity with spectrum regulationdifferences between recreational and “licensed” ra-dio-controlled operations all could come into play.

The narrow perspective of conducting anaccident investigation – especially one solelydevoted to looking for ways to prevent the nextaccident and chartered as such by national laws –may help investigators avoid having to address theseparate and distinct issues of liability, conformityto existing rules as opposed to their adequacy, andso forth. Still, even identifying the operator of suchan aircraft could be challenging under some cir-cumstances. This issue will be explored in moredetail below.

A few States have taken the first steps towardestablishing rules for UAS at the smaller end of thesize spectrum and distinguishing between recrea-tional and civilly regulated remotely piloted air-craft (the preferred term of art in some circles).This has been a matter of some urgency in Europe,where movement toward establishing a regulatoryframework for aircraft with takeoff weights in ex-cess of 150 kilograms (330 pounds) has created aconcomitant need for individual States to establishrules for the operation of UAS below that thresh-old.13

In the United States, Public Law 112-95 (theFAA Modernization and Reform Act of 2012) makesit clear that model aircraft are a subset of the larg-er family of unmanned aircraft, while at the sametime prohibiting the Federal Aviation Administra-tion from making any rules governing their opera-tion. However, it also limits model aircraft opera-tions to the following conditions (Section 336):

(1) The aircraft is flown strictly for hobby or rec-reational use;

(2)The aircraft is operated in accordance with acommunity-based set of safety guidelines andwithin the programming of a nationwide commu-nity-based organization;(3) The aircraft is limited to not more than 55

pounds unless otherwise certified through a design,construction, inspection, flight test, and operationalsafety program administered by a community-based organization;

(4) The aircraft is operated in a manner thatdoes not interfere with and gives way to anymanned aircraft; and

(5) When flown within 5 miles of an airport, the

operator of the aircraft provides the airport opera-

tor and the airport air traffic control tower (when

an air traffic facility is located at the airport) with

prior notice of the operation (model aircraft opera-

tors flying from a permanent location within five

miles of an airport should establish a mutually-

agreed upon operating procedure with the airport

operator and the airport air traffic control tower

(when an air traffic facility is located at the air-

port)).A model aircraft not meeting all of these criteria

could be construed as a de facto small UAS, forwhich the United States and most other Stateshave yet to issue formal operating rules. Regard-less, if a model aircraft is involved in any sequenceof events requiring investigation, its legal status(use, location, etc.) will need to be documented andevaluated in terms of how any of those factors mayhave contributed to the observed outcome.

On the other hand, if it can be demonstratedthat the outcome would have been no different hada formally certificated UAS instead of a model air-craft been involved (as where no difference may ex-ist between a manned or an unmanned aircraft’sinvolvement, as suggested above), investigatorsshould document that fact as well to ensure hobby-ist activities are not unreasonably brought intoquestion or unfairly constrained.

Separate from a model aircraft’s legal operatingstatus, investigators may face a number of purelyinvestigative challenges similar to those associatedwith small UAS accidents, including: Identifying and locating the operator of the

model aircraft; Confirming the exact type of model aircraft in

use; For midair collisions, determining the exact tra-

jectories of both aircraft relative to each otherat the time of impact; and

Reconciling the observed impact damage withthe physical properties of the model aircraft.

The last could be important because, unlikesmall UAS manufactured in accordance withASTM F2910, Standard Specification for Designand Construction of a Small Unmanned AircraftSystem (sUAS), model aircraft are not customarilydesigned in consideration of: Maximum speed; Maximum weight;

Minimization of the likelihood of fire, explosion,or the release of hazardous chemicals, materi-als, and flammable liquids or gasses, or a com-bination thereof, in flight or in the event of acrash, hard landing, or ground handlingmishap;

Containment of post-crash fire;

26

Protecting first responders from hazards at thecrash site;

Use of flame-resistant materials; Use of energy-absorbing structures; or Protection against battery-induced fires.14

The criticality of a model aircraft’s physicalproperties as observed following its impact withanother aircraft, a person, or an object on theground all will need to be evaluated against theASTM criteria to determine if they are relevant tothe observed outcome.

CHAPTER 4Annex 13 to the Convention on Interna-tional Civil Aviation: Recommendations

Relative to UAS Investigations

Recommendation Regarding Determiningthe State of OccurrenceThe State of Occurrence for an unmanned aircraftaccident should be determined in the same manneras is currently used to make such determinationsfor manned aircraft accidents.

Special Circumstances Where AdditionalAccredited Representatives May BeWarrantedProvisions should be made allowing for additionalaccredited representatives to investigations involv-ing unmanned aircraft systems as follows:

State of Design—If the State of Design for theaircraft differs from the State of Design for theground control station in use at the time of an acci-dent, both States should be invited to provide ac-credited representatives.

State of Manufacture—If the State of Manu-facture for the aircraft differs from the State ofManufacture for the ground control station in useat the time of an accident, both States should beinvited to provide accredited representatives.

Aircraft and Ground Control Station Regis-tered in Different States—If an unmanned air-craft system involved in an accident has its aircraftregistered in one State and its ground control sta-tion registered in another State, both States shouldbe invited to provide an accredited representativeto the investigation; however, the investigatingState should specifically determine if certificationcompatibility issues played any part in the accidentsequence.

Location of Pilot/Operator Different fromState of OccurrenceThe location of the ground control station – andthus, the pilot in command – of an unmanned air-craft system may be different from both the State ofthe Operator and the State of Occurrence. Consequently if a pilot in command is operating

an unmanned aircraft under the rules of theState of the Operator at the time of an accident,the location of the ground control station shouldnot result in an automatic invitation to thehosting State to provide an accredited repre-sentative unless an infrastructure issue underthe control of that State (e.g., electrical power,telecommunications availability) may haveplayed a role in the accident sequence.

If a pilot in command is operating an un-manned aircraft under the rules of a State host-

ing the system’s ground control station – otherthan the State of the Operator or the State ofOccurrence – at the time of an accident, thehosting State should be invited to provide anaccredited representative.

CHAPTER 5Data Fields Associated with UASOperations Requiring Capture

OverviewThe Commercial Aviation Safety Team (CAST)

and the International Civil Aviation Organization(ICAO) have a standing Common Taxonomy Team,known as CICTT. According to its Web site(www.intlaviationstandards.org), the purpose ofthis group is “to remove constraints on aviationsafety analysis and sharing. These constraints arecreated by the lack of common global descriptors ofaviation safety events and standards for aviationsafety data and information.”

CICTT’s work is aimed at developing standardsfor safety data collection that would harmonize ex-isting systems with common definitions and termi-nology, working from the ICAO accident reportingsystem (ADREP) as a baseline. The CICTT effortrevolves around developing standard descriptionsfor the following: Aircraft Make/Model/Series

Aircraft Engine Make/Model/Submodel Aviation Occurrence Categories – Per the AD-

REP system, there are fifteen primary occur-rence categories, all of which are accounted for

27

under the CICTT taxonomy: Abnormal runway contact (ARC) Birdstrike (BIRD) Controlled flight into or toward terrain

(CFIT) Collision with obstacle(s) during take-off and

landing (CTOL) Fire/smoke (non-impact) (F-NI) Ground Collision (GCOL) Loss of control - inflight (LOC-I) Airprox/ ACAS alert/ loss of separation/

(near) midair collisions (MAC) Ground Handling (RAMP) Runway excursion (RE) Runway - wildlife presence (RI-A) Runway incursion - vehicle, aircraft or per-

son (RI-VAP) Powerplant failure or malfunction (SCF-PP) System/component failure or malfunction

[non-powerplant] (SCF-NP) Undershoot/overshoot (USOS)

Phases of Flight Human Factors Taxonomy (performance in re-

lation to environment)

Aerodrome Taxonomy Positive Taxonomy (i.e., “What went right to

prevent an accident?”)

CICTT and UASA working group has been established underCICTT, chaired by a representative of the NationalTransportation Safety Board, to modify all of thecommon taxonomies – including “ATA Codes” asneeded – to incorporate UAS-specific data fieldsand descriptors. This is being accomplished in partthrough reference to a working safety databasemaintained by the U.S. Federal Aviation Admin-istration’s Unmanned Aircraft Systems IntegrationOffice.

ISASI UAS Working Group Position andRecommendationsThe position of the ISASI UAS Working Group withrespect to data collection is that unmanned aircraft-involved events should be recorded and mappedthe same as manned aircraft events to the maxi-mum extent possible. The entry of standard power-plant identifiers may be complicated by the not-infrequent use of non-aviation-certified engines inunmanned aircraft; however, phases of flightshould remain identical to those already in use.The only additions to the Aerodrome standard thatpossibly could be needed might be references to

specialized launch-and-recovery equipment perma-nently or semi-permanently installed on airportrunways or taxiways to facilitate UAS operations.

Accordingly, the three principal thrusts of theCICTT effort with respect to unmanned aircraftsystems should be:

(1) Ensuring that existing occurrence categoriesare sufficiently broad enough to allow the inclusionof UAS-involved events with the same or equiva-lent outcomes;

(2) Adding primary and secondary occurrencetypes to accommodate UAS-related events suffi-ciently different from manned events that they re-quire separate categorization; and

(3) Expanding the human factors taxonomy asneeded to ensure pilot-to-aircraft interface, percep-tion and awareness issues are adequately capturedfor analysis and corrective action.

The CICTT standard Aviation Occurrence Cate-gories: Definitions and Usage Notes, version 4.6(October 2013) discusses some UAS-related issues,but does not do so in a manner that fully distin-guishes the unique failure modes to which un-manned aircraft are susceptible. It also explicitlylimits inclusion of unmanned aircraft to those thathave “a design and/or operational approval,” whichmay exclude future unmanned aircraft systemsbuilt to conform to consensus standards instead ofreceiving formal certification. (This conforms toAnnex 13 criteria for investigations as well.)

In particular, the current CICTT approach toaddressing UAS control link failures is over- broadand conflates unmanned aircraft flight control fail-ures associated with the airframe alone with thoseaffecting the unique electronic link between pilotand aircraft. Under “Loss of Control – Inflight,” thefollowing explanatory note is provided:

For unmanned aircraft events, includes hazard-ous outcomes involving deviation from intendedflightpath associated with anticipated or unantici-pated loss of datalink. However, if loss of datalinkis the direct result of a system/component failure ormalfunction, code the occurrence as System/Component Failure or Malfunction (Non-Powerplant) (SCF–NP) only.15

From the standpoint of being able to identifycauses and make relevant recommendations, is im-portant to distinguish between mechanical/aircraft-based malfunctions resulting in an uncontrollableaircraft from those specifically attributable to theso-called “communications segment” between pilotand aircraft. The intent of designers and regula-tors alike is to have the latter condition result inpredictable behavior that ideally would conclude

28

with the safe recovery of the aircraft.It is equally important to capture events where

the pilot in command has deliberately (or negligent-ly) severed the control link. Such may be the casewhere the flight manual prescribes such action asnecessary to restore control or place the aircraft ina known mode of operation or, alternately, wherethe aircraft is flown into an area where satellitecoverage is not available and/or line-of-sight rangeof the link is exceeded.

The CAST/ICAO Common Taxonomy is intendedto promote and support preventive actions as wellas simply recording events once they have takenplace. Therefore, the ISASI UAS Working Grouprecommends adding three primary occurrences forunmanned aircraft: Loss of Control Link (Two-Way) (LOCL-T): Fail-

ure of the complete control and non-payloadcommunications (CNPC) link between an un-

manned aircraft and its associated remote pilotstation.16

Usage note: Use this coding when controlcommands are not received by the aircraftand the datastream from the aircraft to theremote pilot station ceases.

Loss of Control Link (Uplink) (LOCL-U): Fail-ure of datalink transmission from a remote pilotstation to its associated unmanned aircraft.

Usage note: Use this coding when the pilot in

command (PIC) has no ability to affect the

trajectory of the unmanned aircraft and the

aircraft reverts to a pre-programmed self-

guiding mode but continues to provide per-

formance and positional data to the PIC. Loss of Control Link (Downlink) (LOCL-D):

Failure of datalink transmissions from an un-manned aircraft to its remote pilot station Usage note: Use this coding when the pilot in

command still can direct the trajectory of theaircraft but cannot receive datalinked confir-mation that control commands have beenreceived and/or properly executed.

The ISASI UAS Working Group also recom-mends adding one secondary occurrence for un-manned aircraft: Flyaway (FLYA): Failure of a UAS to conform

to pre-programmed behavior following Loss ofControl Link (Two-Way or Uplink).

CHAPTER 6UAS-Specific Air Safety Investigator Skills

The four principal areas in which unmanned air-craft systems physically differ from manned aircraft– as noted above – are the lack of an on-board pilot,their reliance on RF spectrum for safe operation,their limited and varying abilities to separate them-selves from other aircraft, and their occasional useof novel and exotic materials for construction andpropulsion. As discussed throughout this mono-graph, these differences may manifest themselvesin how an accident sequence plays out, as well as inthe types of recommendations air safety investiga-tors may need to make to prevent the recurrence ofsimilar accidents in the future.

To be prepared to deal with both of these possi-bilities, anyone currently designated by a State toserve as investigator-in-charge of an accident inves-tigation should be provided familiarization trainingregarding unmanned aircraft system characteris-tics and operations as conducted within their areaof responsibility.17 As a minimum, specific topicsshould include: Nationally employed definitions of “unmanned

aircraft” and “unmanned aircraft system” orequivalent terminology (e.g., “remotely piloted

aircraft”) Classification methodology (e.g., size, weight,

speed) used to differentiate among unmannedaircraft

How differences among UAs influence their in-teractions with manned aircraft (e.g., infra-

structure requirements for takeoff and landing,authorized types of operations, etc.)

Applicability of national rules to UAS opera-tions with respect to airspace, altitude, etc.

UAS certification procedures. Authorized spectra for the control of unmanned

aircraft.The syllabi of training courses used to certify

future investigators in charge should incorporatesimilar material as well.

Beyond ensuring that generalist investigatorshave at least a basic understanding of the above,investigative authorities need to ensure that desig-nated ASIs have access to specialists possessing theexpert knowledge needed for detailed exploration ofthe issues described in Chapter 3. In particular,ASIs must be prepared to delve into in-depth inves-tigations of the vulnerabilities and dependenciesamong the different components linking the pilot in

29

command with the unmanned aircraft, as well asthe unmanned aircraft’s behavior in the event of afailure of any part of the “communications seg-ment.” Effectively conducting an investigationwhere such issues arise will be extremely challeng-ing, and advance identification of resources to sup-port it will be the key to the ASI’s ultimate success.

CHAPTER 7Evidence Preservation Following

Unmanned Aircraft System Accidents

On-Scene and Ground Control StationInvestigationsThe on-scene investigation of an accident involvingan unmanned aircraft may be complicated by anumber of factors, most notably: Determining that an unmanned aircraft

actually was involved due to limited residualphysical evidence; and

Limited numbers of identifiable or identifyingcomponents (e.g., parts with serial numbers).Similarly, investigators faced with an accident

with unmanned aircraft involvement must re-member that it is possible that much of the mostcritical evidence related to the unmanned air-craft’s operation leading up to the occurrence maynot necessarily be found at the scene (althoughsome autopilot- related avionics may yield usefuldata in some cases). They will need to locate andsecure the “cockpit” – the ground control station –and apply expert knowledge to the technical prob-lem of retrieving from it everything relevant to theunmanned aircraft’s operation leading up to theoccurrence itself.

Testimony from the Pilot-in-Commandand Other Crew MembersLocating the pilot in command and tracing theownership of unmanned aircraft involved inaccidents conceivably could be the single mostdifficult task facing air safety investigators lookinginto events involving UAS. Therefore, investigatingauthorities should consider establishing rules – orrequesting the passage of laws – addressing: The pilot in command’s duty to self-identify

when their aircraft is involved in an accident,incident or unusual occurrence, or fails to re-turn from a flight.

The obligation of operators to incorporate ameans of identifying the aircraft (registration,

serial number, etc.) that will survive impactforces and post-crash fire.

The preservation of ground control station-based data relevant to the accident flight, in-cluding both aircraft performance and payload-provided data available based on the configura-tion of the system at the time of the occurrence.

CHAPTER 8UAS Investigation Procedural and

Functional Considerations

There are two basic considerations regarding theincorporation of specialized or novel elements thatmay be part of unmanned aircraft system accidentsequences into existing investigative guidance:

1. Adapting current procedural checklists to cueusers to inquire into UAS-specific issues inconjunction with existing steps/processes ineach investigation.

2. Ensuring current criteria for the developmentof accident final reports incorporate relevantUAS-unique content into both the factualand analytical portions of such reports.

The rapid growth of the unmanned aviation sec-tor means there is significant interest across theair safety investigator community in developing acommon, end-to-end investigation checklist specificto unmanned aircraft systems. However, such aneffort will be extremely work-intensive. The deci-sion was made not to further delay the release ofthe first ISASI UAS Investigation Guidelines toincorporate such a checklist into this document.

By the same token, a number of organizationsaround the world – most notably the CanadianForces – have expended significant efforts towarddeveloping guidance of this type, aligned with cur-rent and emerging ICAO publications. The UnitedStates Army has created a UAS-specific reportingand investigation form (DA Form 2397-U, UAS Ac-cident Report, available at http://armypubs.army.mil/eforms/pdf/a2397_u.pdf) wellsuited to the gathering of operational, environmen-tal, personnel and equipment-related data associat-ed with a given event.

Users of this document are encouraged to con-tact their counterparts in States currently support-ing UAS operations if they need to quickly obtainworking examples or advanced prototypes that canbe used in response to an urgent need. However,priority should be given to examining existing guid-

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ance on an individual basis and modifying it asdiscussed below.

Near-Term Investigation of UASAccidents and IncidentsFor the foreseeable future, every unmanned air-craft system accident and incident investigationhas the potential to be groundbreaking in some re-spect. There are many unknowns regarding theextent to which unmanned aircraft can safely per-form operations currently carried out by mannedaircraft. There are similar unknowns regardingthe safety or practicality of applying unmanned air-craft technology to activities previously consideredunsafe for manned aircraft to conduct.

The only way these issues can be explored objec-tively is through informed consideration of how thetradeoffs, accommodations and legacy rules appliedto unmanned aviation are playing out in real-worldoperations. In a larger sense, each UAS accident orincident represents an opportunity to assess theextent to which the body of rules governing bothmanned and unmanned aviation has adequatelyprovided for the latter. At the same time, investi-gators can provide essential feedback to policymak-ers regarding the effectiveness of the regulatoryapproach in use, the extent to which manned andunmanned operations may be conducted on a coop-erative and/or a segregated basis in shared air-space, and the validity of both use and risk as-sumptions that have been applied to their respec-tive rulemaking challenges.

In the near term, however, air safety investiga-tors must recognize that there are significantly dif-ferent and even competing philosophies regardingthe desirability of regulating unmanned aircraftthe same as manned aircraft, somewhat less strin-gently, or with a minimal level of authority overthem. Perspectives vary from State to State, fromregion to region, and even among different govern-mental, quasigovernmental and standards develop-ment entities chartered to normalize UAS-relatedactivities. Investigators need to understand thecurrent landscape within which UAS occurrencesare taking place to make useful recommendationsaimed at preventing their recurrence. This will notbe an easy task.

Different States are making different decisionsregarding how UAS pilots should be licensed; theamount of training they should receive; and, theextent to which they should cooperate with or avoidsurrounding aviation operations. They are debat-ing airworthiness, certification and registration re-

quirements; equipage minima; and, operating crite-ria. These considerations are being shaped by mar-ket forces such as the emergence of a UAS manu-facturing sector and entrepreneurial applications ofunmanned aviation technology, existing airspacestructure and usage, and a host of other variables.The only truly common goals are to continue toprovide a safe flying environment for all stakehold-ers, and to foster opportunities to take advantage ofemerging UAS capabilities consistent with the needfor safety.

Preliminary ConsiderationsAir safety investigators faced with the possibleneed to investigate an occurrence involving an un-manned aircraft or unmanned aircraft system needto consider several issues.

First and foremost is the question of jurisdictionand investigative authority. If a manned aircraft isinvolved in an accident or incident that meets Statereporting and investigative criteria, the complicat-ing factor of an unmanned aircraft system in thesequence of events in no way prevents the occur-rence from being investigated as usual. However,an accident or incident involving only an un-manned aircraft system must be examined for somepossible complicating elements: Do the State’s rules distinguish between un-

manned aircraft systems used for hobby or rec-reational purposes and those used for other pur-poses, e.g., commercial or business-related ac-tivities? In the U.S., radio-controlled model air-craft flown purely for pleasure are not subject toeither Federal Aviation Administration or Na-tional Transportation Safety Board scrutiny.

Do the State’s rules establish a size thresholdbelow which regulatory oversight is minimizedor not exercised? In some European Unioncountries, UAs below a certain weight (such as25 kg) are not subject to regulation; in others,no rules exist for anything less than 150 kg.

Did the occurrence take place in special use orrestricted airspace not subject to civil aviationauthority? If so, responsible military or law en-forcement entities may be willing to allow civilair safety investigators to participate in theirinternal inquiries, but the terms of such cooper-ation are best negotiated in advance of need.

Was an “optionally piloted vehicle” (OPV) in-volved? An OPV is one certificated to be flownby either an on-board pilot or via CNPC link. Acase may be made that an accident or incidentinvolving an OPV almost always is subject to

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investigation if the civil aviation authority’s de-termination of its airworthiness might be calledinto question.

Once the question as to the investigative author-ity’s right and obligation to conduct an investiga-tion is resolved, the investigation should be treatedas any other. However, a suggested practice thatmay aid the development of recommendations is forthe investigator to note each instance where: Regulatory guidance for unmanned aircraft dif-

fers from manned aircraft; and That difference had a clear effect on either the

sequence of events or the observed outcome.The latter may illuminate challenges associated

with how manned and unmanned aviation opera-tions are being integrated. However, it also pro-vides an opportunity to document cases where theregulatory approach to unmanned aircraft systemscan be shown to have been better suited to theiractivities than manned aircraft requirementswould have been, as seen in a less severe outcomethan otherwise might have been expected.18

Tailoring Local Guidance to IncorporateUAS-Related ConsiderationsTo meet the needs described above, the followingtwo sections contain suggested areas for fact-gathering and/or exploration specifically in thecourse of a UAS investigation. They are organizedfollowing the general outlines for investigationsand final reports set forth in ICAO Document 9756,Manual for Aircraft Accident and Incident Investi-gation, Part III (Investigation) and Part IV(Reporting), respectively.Areas of Investigation-

1. Wreckage (on-scene) investigationThe on-scene investigation of a crashed un-

manned aircraft of any size or type should be con-ducted the same as that of any manned aircraft.The most notable differences that might be encoun-tered would involve the possible presence of unusu-al or potentially hazardous materials (HAZMAT) ineither aircraft structures or the propulsion system;the operator and first responders should be contact-ed to evaluate the risk of these threats prior to ar-riving at the scene.

In the case of an accident or incident involv-ing a line-of-sight system investigators need tocarefully document the pilot in command’s locationrelative to the aircraft, as well of that of any visualobserver(s). Ensure surrounding terrain, struc-tures, time of day, ambient light and sun angle arecaptured as well.

2. Organizational investigationThere is significant potential for the organiza-

tional investigation to be an important part of anyinquiry involving unmanned aviation. As a start-ing point, investigators will need to assess the oper-ator of the UAS in terms of the following: Is it an enterprise dedicated to providing

manned and unmanned aviation-based ser-vices?

Are its services limited to unmanned aviationonly? If so, how long has it been in operationand to what extent is its management structurealigned with the requirements of safely support-ing an aviation enterprise?

Does it use unmanned aviation simply as ameans of furthering other business interests,with its primary activities being unrelated toaviation?Once these basic determinations have been

made, the relationship between the operator andthe person or entity that exerted operational con-trol over the UAS’ flight activity must be estab-lished: How was the mission scheduled and conducted? Who did the pilot in command work for?

Given that UAS have many useful applicationsin the realm of law enforcement and public safety,investigators also must take into consideration theoperator’s risk tolerance and sense of urgency inthe course of carrying out flight operations. Therequirement for risk mitigation plans supportingindividual UAS operations or activities is not uni-versal, but such plans should be sought and re-viewed where available.

3. Operations investigationThe operations investigation of a UAS-related

occurrence should be approached the same as thatof any other accident or incident. However, it isimportant to examine each UAS operation in thecontext of: The activity in progress; Any regulatory structure in place supporting (or

alternately, not anticipating) such activity; The adequacy of flight and operations guidance

(manuals, etc.) supporting the activity in pro-gress;

Expected and unexpected interactions betweenunmanned and manned aircraft;

The number of unmanned aircraft involved inthe specific flight activity of interest at the timeof the occurrence, and how many of those air-craft were operating autonomously or under thecontrol of a single ground control station;

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Any control handoffs that might have been inprogress or incompletely carried out betweenseparate ground control stations at the time ofthe occurrence, the method of control being ex-ercised (e.g., line-of-sight to line-of-sight, line-of-sight to beyond line-of-sight, etc.), and themeans by which one PIC coordinated transfer ofcontrol to the next;The status of the global navigation satellite

system (GNSS) in use at the time of theoccurrence;

Expected and unexpected effects of the un-manned aircraft system on nonparticipants andthe general public;

Means used to advise the public of the presenceof unmanned aircraft operations in a givenlocation (if required); and

The extent to which the UAS operation itselfwas compatible with the airspace and geograph-ical location where it was carried out.Attention also should be given to the extent to

which the pilot in command’s attention may be di-vided between the aviation environment and a loca-tion of interest on the surface, i.e., conflicting“mission” priorities. (See “Investigating humanfactors” below.)

4. Aircraft operational environmentParticular concerns related to UAS operations

and capabilities that should be taken into consider-ation in evaluating the aircraft operational envi-ronment may include: Terrain Weather (VMC versus IMC, rapidly changing,

unforecast winds, etc.) and how the PIC is ableto monitor it

Illumination (daylight, artificial light, etc.) The nature and quality of on-board sensors Pilot workload required to carry out the desired

flight activity Interactions between the pilot in command and

responsible air traffic control facilities The proximity of obstructions to the unmanned

aircraft The proximity of the unmanned aircraft to con-

gested, heavily populated or heavily traffickedareas or open-air assemblies of people (e.g.,sporting events)5. Aircraft performance investigationThe definition of “aircraft performance” in ap-

plying existing investigative processes to un-manned aircraft systems needs to take into consid-eration the entire system, including the perfor-mance of the control and non-payload communica-

tions (CNPC) link as it might be influenced by ter-rain, structures, precipitation, or the surroundingradiofrequency environment. In this context, theground control station must be understood to bepart of the “aircraft” as well.

Conventional “performance” charts showingpower available/required in various flight regimesmay not be available to investigators, necessitatingexperimentation (and the possibility of incurring asecond accident) to properly document the aircraft’soperating envelope.

6. Flight recordersThere are several sources of recorded data that

may be available to support a UAS-related investi-gation, many of which go well beyond the conven-tional meaning of “flight recorders.” Non-volatilememory cards located in the wreckage – both thoseassociated with on-board control operations andthose integral to the payload – may contain usefuldata. On-scene investigators should be provided asmuch information as possible regarding the typesof avionics that may be useful in this role and pro-vided photographs or undamaged examples toguide their efforts.

In addition, the entire ground control stationshould be evaluated with an eye for what might bedesigned specifically with recording in mind versuswhat might contain potentially useful data as a by-product of its performing a normal control or pay-load-related activity. The term “digital source col-lector” is used by some manufacturers and opera-tors to refer to capture systems of this type.

Finally, if the CNPC link was maintainedthrough a ground or satellite-based network, theprovider of network services may possess usefuland relevant data regarding the integrity of thelink itself.

7. Reconstruction of wreckage19

As with manned aircraft, the reconstruction ofwreckage only should be considered for unmannedaircraft if essential to identifying a particular pointof origin for fire or on-board explosion or the site ofan external impact suffered in flight.

For any accidents or incidents involving un-manned aircraft, investigators may find hands-onaccess to a similarly equipped and painted UA ofidentical configuration useful for evaluating: Field of regard (field of vision) of on-board sen-

sors. Antenna locations, especially relative to the di-

rection from which the control signal was ema-nating.

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The visibility of the UA as it would have presented itself to ground-based observers and thepilots of other aircraft.

8. Structures investigationFor the most part unmanned aircraft are

not designed to manned aircraft standards, andtheir airworthiness may not be predicated on exist-ing criteria for manned aircraft. Further, manyunmanned aircraft manufacturers have no experi-ence with designing or producing full-scale aircraft,meaning both the methodologies and their solu-tions to specific design issues (especially those re-lated to weight and endurance) may be unorthodox.Still, for the most part some documented processshould have been applied to the design and con-struction of any unmanned aircraft operated in non-reserved airspace. That process should be used byinvestigators as a starting point for detailed in-quiry.

With the above considerations firmly in mind,investigators will need to proceed objectively ineach case where a structures investigation is essen-tial to establishing the cause of a given accident orincident. Straightforward (and possibly time-consuming) engineering analysis may be requiredto assess the failure mode, the adequacy of thebasic design and the validity of the airworthinesscertification itself.

Investigators also should bear in mind that thelessons of aviation history in some cases are beingre-learned by a new cohort of airframe manufactur-ers. It is possible that the specific failure suspect-ed or observed may never have played a part in ei-ther a manned or unmanned aircraft accident in-vestigation before. However, it is just as possiblethat such failures might have been common in pre-vious generations of manned aircraft, and that de-signs or manufacturing processes abandoned incurrent aircraft manufacture might have been em-ployed in the unmanned aircraft under scrutiny forreasons of simplicity, cost-effectiveness, or ease ofconstruction.

9. Mid-air collision investigationThe possibility of mid-air collisions between

manned and an unmanned aircraft is one of thecatastrophic scenarios forecast by those attemptingto chart a path for the safe integration of un-manned aircraft systems into the existing aviationsystem. To date, however, there have been a barehandful of such incidents recorded in civil aviationoperations.

The investigation of an unmanned aircraft-involved midair collision should proceed as anyother such investigation. However, the alternate

means of compliance being used to compensate forthe UA’s lack of onboard see-and-avoid capabilitymust be thoroughly scrutinized and its effective-ness fully established. The three most commonmeans of clearing an unmanned aircraft’s flightpath are:

a. Ground-based visual observer (either the pi-lot in command or a person fulfilling a pure-ly observer role).

b. Airborne visual observer (from a chase plane,either the pilot or a separate crewmember).

c. Electronic “sense and avoid” systems; theseare subdivided further into –

Ground-based sense and avoid (GBSAA) sys-tems using dedicated radar systems or a func-tionality reliant on existing air traffic controlradar coverage; or

Airborne sense and avoid (ABSAA) systemsconsisting of either:

A purely aircraft-based system that can de-tect non-emitting and/or emitting aircraftand autonomously execute an avoidance ma-neuver; or

An aircraft-based surveillance system thatprovides situational awareness data via adownlink to the pilot in command for appro-priate action.

Investigators need to understand all of theaviation system components available for keepingaircraft separated as they operated during the acci-dent or incident sequence, including any systemlogic that may have been used by a UAS DAAsystem in trying to keep a VFR operation “wellclear” of other aircraft.

10. Fire pattern investigationThe need for any fire pattern evaluation will be

dictated by the circumstances surrounding the lossof a given unmanned aircraft. Since occupants arenot at risk, any such investigation reasonably maybe confined to the propagation of an on-board firefrom its point of origin to where it could have hadan effect on flight-critical components.

11. Powerplant InvestigationA powerplant investigation – if deemed neces-

sary in the course of the inquiry based on the pre-sumed sequence of events – is likely to be some-what less straightforward than that of other inves-tigative activities for the foreseeable future. Theaviation expertise of airframe and powerplant ex-perts may not be applicable to the propulsion sys-tem used by an unmanned aircraft involved in anaccident.

Unmanned aircraft may be powered by normal-ly aspirated or supercharged piston engines. They

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may be equipped with turboshaft or turbojet en-gines. They may run on electric motors, poweredby batteries, solar power, or even fuel cells. Theymay use separate on-board power supplies for pro-pulsion and payload, or meet all on-board powerrequirements with engine-driven generators or al-ternators.

In particular, the relationship between the un-manned aircraft’s powerplant and its other systems– especially its CNPC-related avionics – may becritical to understanding an observed failure or se-ries of failures. It could be that an engine shutdown because it was designed to do so as a safetyfeature following a separate failure. It also couldbe that an engine shutdown was an unexpectedconsequence of a previously unsuspected sneak cir-cuit or similar unanticipated system-level failure.Regardless, given the innovation applied to solvinga variety of operational problems and limitationsthat arise in unmanned aircraft design, investiga-tors must be prepared to enter uncharted territoryas they enter into each new powerplant investiga-tion.

Investigators also must be alert to the possibil-ity that an unmanned aircraft’s engine might be inuse in manned aircraft as well, although perhapsas an aviation-certified variant of a non-aviationdesign. For example, some light sport aircraft en-gines are adapted from motorcycles, snowmobilesand similar efficient, high-torque uses. However,many of these engines conform to aviation-specifictechnical standard orders. Without knowing thedifferences between the certified and non-certifiedversions of such engines, investigators cannot knowif a failed engine component observed in a UA acci-dent is shared by its manned counterpart.

12. Systems investigationFor the most part, UAS “systems” investiga-

tions will be similar to and in some cases less com-plex than those supporting manned aircraft. Themost notable exceptions to this general rule are: Evaluating and verifying the integrity of the

entire CNPC link, from the pilot’s hands to thecontrol surfaces or actuators. (The NTSB andother entities consider a CNPC failure a flightcontrol malfunction.)

Ensuring the proper function of avionics andother systems not unique to unmanned avia-tion, but whose design does not conform to es-tablished standards or technical standardorders required of manned aircraft.

Assessing the accuracy and adequacy of the in-formation downlinked to the pilot with respect

to the aircraft’s performance, trajectory,position and condition.The last of these three could be particularly

challenging, and might require out-of-the-boxthinking and interactions between systems engi-neers and human factors experts in the course ofthe investigation itself. (See “Investigating humanfactors” below.)

Most air safety investigators will find it famil-iar and convenient to focus on known or suspectedCNPC failures as part of broader “systems” investi-gations. In such cases, several key pieces of factualinformation need to be established early in the in-vestigation, particularly with respect to the “lostlink” program the unmanned aircraft wasprogrammed to follow: How long was the aircraft supposed to wait to

re-establish contact with its GCS beforeinitiating its lost link behavior?

Did the aircraft follow its pre-programming incarrying out its flight to its rally/home/ flighttermination point?

Was the location to which the unmannedaircraft was required to autonomously navigatefollowing a CNPC failure appropriate to theoperation? To the airspace? To thesurrounding terrain?

Was the CNPC failure accompanied bycomplete loss of the pilot’s awareness of theaircraft’s location?

Was the CNPC failure accompanied by otherfailures resulting in air traffic control’s inabilityto monitor its route of flight from the point offailure to its designated rally/home/ flighttermination point?Associated with this issue is the extent to which

the system under investigation requires some formof interaction between CNPC link data (which maybe conveyed within a reserved or protected part ofthe electromagnetic spectrum) and payload datasuch as cameras and other sensors not operatingwithin UAS-specific frequencies.

Finally, investigators confronted with evidenceof a CNPC malfunction of some type must resistthe temptation to automatically treat such anoma-lies as the cause of the occurrence under investiga-tion. A control link can be compromised by a num-ber of conditions, either internal or external to theaircraft or the larger unmanned aircraft system.

13. Maintenance InvestigationMaintenance investigators may find themselves

confronted by a variety of challenges,including:

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Lack of technical data Lack of standard aircraft record-keeping Lack of clearly defined flight-critical systems Lack of established maintenance intervals for

systems or structuresAlthough some work is underway to establish

ATA codes for failed components specific to UAS,no broad scheme for doing so has been generallyaccepted to date. The CAST/ICAO Common Taxon-omy Team (CICTT) is addressing this issue.However, it is likely to be several years before anyresulting standardized reporting and trackingframework is mandated for UAS manufacturersand operators, meaning the extent and quality ofrecord-keeping may vary widely from one user orsystem to the next.

Based on the above, it is recommended thatmaintenance investigators work to assemble evi-dence and records in a manner as similar to a regu-lar aircraft investigation as possible. Such effortsshould include all components of the unmannedaircraft system, from the ground control stationthrough the communications segment to the un-manned aircraft itself. Any cases where existinglaws or rules inhibit the collection of such materi-als (such as that owned or maintained by telecom-munications providers) should be flagged for sepa-rate action following the completion of the investi-gation, when its absence can best be assessed.

14. Helicopter InvestigationFor the most part, unmanned aircraft systems

have yet to be formally categorized in a mannerthat aligns with their manned equivalents. Just aslighter-than-air unmanned aircraft are not neces-sarily treated as blimps, airships, dirigibles orballoons, rotary-wing unmanned aircraft tend notto be explicitly identified as “helicopters.”Nevertheless, except where the UAS incorporates anovel combination of technologies to achieve spe-cialized performance or endurance capabilities, ittypically will be appropriate to conduct investiga-tions involving their loss or malfunction as if theywere the manned system they most resemble. Thisallows them to be examined in terms of generallyunderstood expectations regarding their design andperformance.

For rotary-wing UAS, the basic questions to beasked are: How many rotors and how many powerplants

does the aircraft incorporate? What is the effect of the failure of one or more

of the powerplants?

For an electrically powered rotary-wing UA,what is the effect of gradual depletion of thepower supply? Will the aircraft compensate fora dying battery automatically, or must the pilottake action to recover it safely?

What is the effect of the failure of one or morerotor system?

Is the aircraft self-stabilizing in one or moreaxes, or must the PIC continuously monitor theUA’s operation to ensure its stability?

Was the aircraft operated in an environmentwhere its CNPC link was likely to be compro-mised? If so, what is the expected aircraftbehavior upon link failure?

If there were other rotary-wing aircraft in thevicinity of the accident/incident UA, how weretheir operations de-conflicted before and duringthe operation leading up to the occurrenceunder investigation?15. Investigating Human FactorsThere have been a number of research projects

and academic studies carried out to date regardinghuman factors considerations associated with un-manned aviation (see Appendix 2, System Safetyand Human Factors Studies). However, for themost part these draw upon specific experimentaldesigns or inferences regarding how unmanned air-craft can and should be flown. Air safety investiga-tors will greatly increase the understanding of therelative importance of different aspects of the un-manned aviation experience by documenting when-ever and wherever its unique attributes contribute,lead to or directly result in an accident or incident.

Given the newness of the sector and the limitedamount of data available regarding the involve-ment of both traditional and UAS-unique humanfactors, there is no clearly defined set of occurrenc-es deserving special attention from investigators.However, the following should be documented forfollow-on study even if they do not appear to bedirectly related to the accident or incident sequenceat hand: The level of pilot training and expertise

required by the activity versus the specificconditions encountered in the course of theactivity under investigation.

The pilot’s means of exercising control over theaircraft (e.g., handheld controller, keyboard andmouse, “cockpit” emulation, etc.).

Differences between manned and unmannedaircraft pilot tasks required to carry out a spe-cific type of operation or flying activity.

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Instances where habit transference frommanned aviation resulted in the inappropriateor incorrect operation of an unmanned aircraft.

The amount and type of feedback provided tothe PIC regarding the performance and condi-tion of the unmanned aircraft (including theavailability and use of “first person view” tech-nology, tactile feedback provisions, etc.).

Displays and warning systems alerting the pilotto impending or actual hazards (in place andfunctioning during the event or needed, as ap-propriate).In addition to the classic “human/machine in-

terface” issues suggested by the above, human fac-tors investigations also need to consider the suita-bility of UAS technology or platforms being appliedto the specific task in progress at the time of theoccurrence. This is a somewhat different take onhow decision-making issues usually are explored inthe course of an investigation.

Investigators historically tend to focus onwhether a given accident sequence was started orsustained by improper decisions based on incom-plete information or improper risk assessment.While there are many advantages to unmannedaviation, there are purely operations-based disad-vantages as well, although many are not necessari-ly taken into consideration at the time the decisionis made to carry out a given operation.

As observed earlier in these UAS InvestigationGuidelines, unmanned aircraft systems are highlyprized for conducting “dull, dirty and dangerous”activities. This perspective is based on the removalof a human from exposure to a hazardous environ-ment, or one where inattention is likely to interferewith his or her proper performance of the aviationtask. However, there are aviation-based taskswhere the physical separation of the pilot from theaircraft tends to reduce the margin of safety of theoverall operation by virtue of their inability to in-stantly perceive and respond to an abrupt or unex-pected change in the flying environment.

Investigators should be alert to the tendency forhumans to “perceive everything as a nail when theyhave a hammer” and make an independent judg-ment as to the suitability of the use of an un-manned aircraft system in any operation duringwhich an accident or incident occur.

16. Survival, evacuation, search, rescueand fire-fightingThe biggest challenge associated with any UA-

related search and recovery activity typically willbe in locating the wreckage itself, particularly for

smaller unmanned aircraft. However, when ap-proaching the scene of an unmanned aircraft acci-dent – especially one involving a system with whichthe investigators are not personally familiar – on-scene personnel should be alert to the possible pres-ence of latent hazards associated with the un-manned aircraft itself, such as specialized fuels,high-capacity electronic components, high voltagebatteries, or materials emitting toxic by-products ofcombustion.

Post-crash fires associated with and confined tounmanned aircraft crashes may be of significantlyshorter duration than those involving manned air-craft simply because of the lack of interior furnish-ings, primary or supplemental oxygen systems andother components that tend to prolong manned air-craft fires. However, high altitude long endurance(HALE) UAS may contain a surprising amount offuel supporting their long-range performance. So,both firefighters and investigators need to applythe same standards of crash site safety to a UASaccident scene they encounter as they would anyother aircraft accident scene.

Injuries or subsequent occupational illnessesexperienced by first responders should be trackedby investigators wherever novel materials or fuelsare known or later identified as having been pre-sent at a crash scene. If necessary, a system forreporting such illnesses should be created wherenone currently exists.

17. Pathology InvestigationThe only time in-depth investigations into this

subject area should be required are in cases whereeither (a) a UAS crewmember died or was incapaci-tated, or (b) where UAS involvement in an accidentdirectly resulted in a fatality or injury. Otherwise,routine toxicological testing of participants shouldbe conducted as would be the case for any compara-ble event involving a manned aircraft.

18. Investigation of [explosives] sabotageWhile this portion of Doc 9756 is narrowly con-

cerned with criminal attacks against manned air-craft, UAS investigators should ensure that thepossibility of any form of intentional interferencewith an unmanned aircraft’s operation is a part of aUAS accident investigation resulting in fatalities,injuries or significant property damage until it canbe definitively ruled out.

Purely electronic attacks – which may be diffi-cult to prove through physical evidence alone – maycome in the form of:

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Meaconing (deliberate misdirection of the air-craft through interference with its navigationalinputs).

Intrusion (deliberate misdirection of the aircraftthrough the transmission of misleading air traf-fic control directions to the pilot by any means;alternately, external takeover of an unmannedaircraft by an unauthorized operator).

Jamming (targeted disruption of CNPC links). Interference (broad-spectrum disruption of an

entire channel or frequency).19. Investigating system design issuesUnmanned aircraft systems tend to be designed

with specific applications and functionality inmind. The priorities in the design of the airframeitself tend to relate to measures that will increasepayload, range/endurance, or both. The lack ofcertification standards to date has resulted insignificant technological innovation, but also atendency to steer away from redundancy in criticalsystems due to their associated weight and/orelectrical power penalties.

Where single-point failures initiated, contribut-ed to or sustained an accident sequence, theyshould be fully documented. Other designconsiderations have been addressed in appropriatesections above.

20. Other unmanned aircraft system-related issuesThe one truly unique aspect of unmanned air-

craft operations (apart from the systems’ relianceon CNPC links) is the need for alternate means ofcompliance with the near-universal requirement forpilots to see and avoid conflicting traffic, obstaclesand terrain. Some of these requirements may bemet by use of detect and avoid systems of varioustypes (see “Mid-air collision investigation” above).However, many DAA systems are intended solely tokeep a UA clear of other aircraft, and do notincorporate any kind of terrain awareness andwarning system (TAWS) logic or functionality.

Investigators considering the possibility of acontrolled flight into terrain (CFIT) scenarioinvolving an unmanned aircraft need to understandthe information available to the PIC as well as thesystem design; in some cases, GNSS-generatedaltitudes may be used where the reference datumsignificantly differs from where “sea level” or“ground level” might actually exist.

Another novel aspect of unmanned aviationwhich may come to light, particularly in the courseof the systems investigation, is the means by whichthe pilot’s inputs are translated into control surface

movements. There are several means by whichUAS designers have solved this technical problem,many of which adapt off-the-shelf autopilots, flightmanagement systems or even hobbyist radio-control systems to UAS use.

As a rule of thumb, the more complex the seriesof transactions necessary to translate a pilot inputinto an aircraft maneuver, the greater theopportunity for software error, hardware malfunc-tion, or single-point failures to occur. There havebeen UAS accidents resulting from obscure failuresin the conversion of commands from one languageto another, as well as in the fidelity of signalstransmitted by systems less (and occasionallymore) complex than required by the scope of controlthey exercise over the aircraft as a whole. Whilethese points were mentioned in the “Systemsinvestigation” section above, they bear repeatinghere: the radiofrequency limitations of CNPC addcomplexity and vulnerability to the system, but anintact link is capable of transmitting faulty com-mands as well as correct commands executedincorrectly upon receipt.

Finally, it is important to note the possibleinvolvement of traffic alert and collision avoidancesystems (TCAS) in unmanned aircraft-relatedaccidents or incidents where a collision, near mid-air collision or loss of safe separation takes place.TCAS algorithms were not created with unmannedaircraft in mind; their performance is substantiallydifferent in some cases, they may climb or descendat different rates than comparable aircraft, andsome have limitations on the extent of bank theycan handle based on their aerodynamic properties.Moreover, most transponders used to emit signalsrecognizable by ATC radar beacon systems havenot be built to existing TSOs, meaning the responseof TAWS systems detecting them cannot beconsidered predictable or reliable.

Any sequence of events involving the loss ofsafe separation between a manned and anunmanned aircraft should consider the possibilitythat TCAS might have played a part in misleadingone or both pilots if (1) the manned aircraftinvolved was TCAS-equipped, or (2) the unmannedaircraft was designed with a “TCAS” function thatcould have been in use at the time of theoccurrence.

38

Final Report Content1. Factual information

History of the flight: Ensure the purpose ofthe unmanned aircraft system’s operationand the operator’s level of aviation expertiseare addressed.

Injuries to persons: Specifically identify inju-ries directly caused by an unmanned air-craft itself; injuries caused by damage to amanned aircraft leading to a subsequent ac-cident should be treated as incidental to thefact that the accident sequence was startedor sustained by an unmanned aircraft’s in-volvement.

Damage to aircraft: Document as for mannedaircraft accidents. If the ground controlstation suffered damage resulting in itsabandonment or the loss of control over theunmanned aircraft, ensure that thesequence of events accurately describes thechronology of the entire failure scenario,starting with the ground-based initiatingevent(s) as appropriate.

Other damage: Document as for mannedaircraft accidents.

Personnel information: Document as formanned aircraft accidents. Specifically ex-amine pilot/observer/other participant quali-fications against minimum requirementsestablished by the State of Occurrence. Beprepared to address any disparity betweenthe level of training or proficiency requiredby rules and the demands of the activity inprogress at the time of the occurrence.

Aircraft information: Document as formanned aircraft accidents. Ensure that fullparticulars are gathered with respect to theunmanned aircraft, the ground control sta-tion, and the network/satellite system (ifany) in use at the time of the occurrence.

Meteorological information: Document asfor manned aircraft accidents. Ensure thatambient lighting and the presence of ceilingsor obscurations to vision from a ground-based perspective are noted whereappropriate.

Aids to navigation: Document as for mannedaircraft accidents. If equipped with naviga-tion-specific equipment, the unmanned air-craft should have a means of transmittingits location and trajectory to the pilot incommand; document if that downlink is partof the primary control system or is provided

via a separate channel. If the system makesuse of global navigation satellite system(GNSS) information, ensure that the statusof the supporting constellation at the time ofoccurrence is documented. Note if the UASis equipped with receiver autonomous integ-rity monitoring (RAIM) equipment. Note ifthe navigation system represents a single-point failure opportunity or if back-ups (e.g.,inertial navigation system) are provided.

Communications: Document as for mannedaircraft accidents. Include all informationrelevant to the status and specific CNPClink architecture in use, including band(e.g., L-band, C-band, Ku-band, non-protected spectrum), data rate, etc. Also de-scribe any hand-off of control from one GCSto the next in progress at the time of the oc-currence in this section if relevant.

Aerodrome information: Document as formanned aircraft accidents. If UAS-uniqueground support equipment (e.g., catapults,rail launching systems, arresting gear) wasrequired and in use at the time of the acci-dent, include such information in this sec-tion.

Flight recorders: List all devices from whichrecorded data was obtained from the un-manned aircraft and the ground station, aswell as that captured by any third-party pro-viders of networked CNPC services.

Wreckage and impact information: Docu-ment as for manned aircraft accidents. En-sure specific locations of ground-based par-ticipants relative to the aircraft and sur-rounding obstacles to visual or electronicline of sight are depicted where appropriate.

Medical and pathological information: Doc-ument as for manned aircraft accidents.

Fire: Document as for manned aircraft acci-dents.

Survival aspects: Document as for mannedaircraft accidents if relevant.

Tests and research: Document as for mannedaircraft accidents. Distinguish among out-side analyses previously completed and ap-plied to the investigation, projects specifical-ly conducted to support the investigations,and follow-on projects needed to support oraffirm the validity of specificrecommendations.

39

Organization and management infor-mation: Characterize the involved UASoperator as – A public use operator performing govern-

mental or public safety functions A provider of manned and unmanned avia-

tion services A provider of exclusively unmanned avia-

tion services A user of unmanned aircraft systems whose

primary business employs manned aircraftas part of its overall enterprise (e.g., aerialphotography, utility patrol, cartography)

A user of unmanned aircraft systems whoseprimary business is enhanced by but notreliant upon aviation as part of its overallenterprise (e.g., real estate, livestockmanagement, agriculture)

Additional information: Document as formanned aircraft accidents.

2. AnalysisFlight operations: Specifically address

any of the following as appropriate – Crew qualification: document if crewmembers –

Conformed to State rules for manned air-craft pilots

Conformed to State rules for unmanned air-craft pilots/other crewmembers

Had no rules in place applicable to the oper-ation in progress at the time of occurrence

Operational procedures Weather Air traffic control Communications Aids to navigation: note if GNSS was required/

available and if any other aids to navigationwere available to the PIC.

AerodromeAircraft: Specifically address any of the

following as appropriate –

Maintenance Performance Weight and balance Instrumentation Systems

Human factors: Specifically address any ofthe following as appropriate – Physiological. Factors which incapacitate, con-

fuse, disorient, distract or dull perceptions, in-cluding: Disease or illness Pharmacological effects

Psychological: Task-Saturation Awareness Decision-making Insight Affective Behavior Psychomotor Complement Perceptual issues Habit Interference Knowledge Judgment Personality Fatigue Learning Background Motivation Personal Discipline

Psychosocial. Factors with indirect influenceson performance, generally involving how theindividual relates to others or groups: Stress Supervision Communication

Ergonomic. Ground control station/handheldcontroller visibility, fit and reach issues relativeto the physical dimensions of the human.

Survivability: Document as for mannedaircraft if appropriate.

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Mezzi Aerei a Pilotaggio Remoto (or “RemoteControl Small Unmanned Aircraft”), the initialdraft of a proposed new Italian regulation for un-manned aircraft systems (UAS), is not availablein English at this writing. (Only one page on theEnte Nazionale Per L’Avianzione Civile (ENAC)official site, plus selected links from it, is inEnglish – see http://www.enac.gov.it/servizio/info_in_english/index.html.) The draft regulationcontains a number of points of interest on issuesrelated to both civil aviation authorities and in-vestigators who may need a frame of reference asto how some of the issues discussed in these UASInvestigation Guidelines have been addressed inan operational context.

ENAC draws a clear distinction between UAS(sistemi aeromobili a pilotaggio remote/ SAPR)and model aircraft (aeromodelli): “Neither theactivities carried out by unmanned aircraftsystems nor model aircraft are currently governedby ENAC, so it is therefore necessary to define aregulatory framework enabling their safe opera-tion.” In addition to addressing model aircraft,the draft regulation is aimed at two distinct UASsectors: those using unmanned aircraft weighingless than 20 kg (44 lbs.) (which will not be issuedairworthiness certificates), and those weighingbetween 20 and 150 kg (330 lbs.).

The upper 150 kg limit is based on EuropeanParliament and European Council Regulation(EC) 216/2008 “on common rules in the field ofcivil aviation;” Annex II of that regulation exemptsunmanned aircraft below that threshold fromEuropean-level regulation, so the Italianregulation is in part intended to ensure there is noregulatory gap involving UAS in their nationalairspace.

The draft regulation provides a European Avi-ation Safety Agency-compliant definition andframework for “special operations” authorizationsthat resembles a combination of the U.S.Certificate of Waiver or Authorization (COA) andSpecial Airworthiness Certificate processes, aswell as several useful definitions: Visual Line of Sight (VLOS) – “Operations are

carried out under conditions and at such dis-

tances that the remote pilot stays in visual con-tact with the aircraft, without the help ofoptical and/or electronic [aids], and inaccordance with the rules applicable to the af-fected airspace.”

Beyond Line of Sight (BLOS) – “Unlike VLOS,operations are conducted at a distance so as notto allow the remote pilot to remain in direct andconstant visual contact with the aircraft, or toabide by the rules applicable to the affected air-space.”

Congested Area – “Areas used as commercial,industrial, residential or sports areas whereyou may have permanent, or even temporary,gatherings of people.”

Sense and Avoid – “Any features on board thatallow the separation of aircraft, equivalent tosee and avoid, in accordance with the rules ofthe air for aircraft with a pilot onboard.” [emphasis added; a ground based senseand avoid system is not acceptable under Ital-ian regulations]

UAS [Visual] Observer – “A person specificallydesignated by the operator who, through thevisual observation of the unmanned aircraft,shall assist the remote pilot’s safe conduct offlying by assisting him in maintainingcompliance with rules of the air, and by provid-ing directions to the pilot to prevent potentialcollision conditions with other traffic andprevent emergency situations.”

Two interesting provisions in the Italian regula-tion are:(1) Unmanned aircraft must give way to all otheraircraft; in return, an explicit assumption is madethat other pilots most likely will not be able to seethe unmanned aircraft in order to avoid it; and(2) Direct overflight of virtually all types of infra-structure (power plants and transmission lines,railroad stations and tracks, dams, military facili-ties, ports, hospitals and prisons), including high-ways, is prohibited except where specifically ap-proved.

The Italian draft regulation sidesteps their cur-rent problem of lacking certification standards byrequiring all of their small UAS certifications to be

APPENDIX 1Significant Aspects Of The Draft Italian Unmanned Aviation

Regulations

41

issued as “restricted” type certificates (for the heav-er aircraft) or “permits to fly” for the smaller ones.It states that optionally piloted aircraft currentlypossessing their own type certificates may be certi-fied as unmanned aircraft based on those certifi-cates plus a separate certification of compatibilitywith the other components in the total unmannedaircraft system of which it is a part.

Also, the Italian draft regulation offers a usefultake on qualifying for certification or “specialoperations” by providing for such authorizations tobe granted once initial test flights have been suc-cessfully and safely accomplished, a formal riskassessment performed, and operators certify: Operations can be conducted safely and

securely in proposed locations and airspace, un-der limits prescribed by ENAC.

The pilot is licensed and has been trained intype.

The operator has adequate liability insurance.

An operations manual has been developed thatdescribes procedures for safe operation of theUAS, including the maximum distance at whichthe system may be operated and the unmannedaircraft seen by its pilot or observer.

The UAS hazards of the greatest concern to theItalians appear to be: “Loss of control of the unmanned air-

craft” (perdita del controllo del mezzo); Loss of containment within assigned airspace

([perdita] fuoriuscita dal volume assegnato); Inability to land safely or terminate the flight

in case of emergency; and

Collision threat to persons and other aircraft inthe air.Italian small UAS pilots will be required to

have one of the three certificates (civil, sport orcommercial) prescribed by European regulationsas well as a Class II medical, and requires them tomaintain currency by performing and logging atleast three takeoffs and landings every 90 days.Small UAS operations will require conformity toall rules of the air, including equipage require-ments as applicable based on the class of airspaceto be used; interim relief is granted from see-and-avoid requirements under VLOS as noted above,but BLOS operations are limited to day VMC insegregated airspace until certified systems ena-bling “sense and avoid” of conflicting traffic, aswell as capabilities for remaining clear of cloudsand surface obstructions, are available.

Some of the equipment requirements levied bythe Italian regulation are noteworthy. In particu-lar, flight termination must be possible either man-ually or automatically, where “termination” meansthe execution of an emergency landing. This capa-bility must be available even when the control linkhas failed. The purpose of this capability is toensure the unmanned aircraft remains within itsauthorized operating airspace at all times. Theregulation also makes it clear that link stability isan issue of both safety and security, and that thetype of link selected for a given operation takes intoconsideration where that operation is to beconducted.

One brief portion of the draft regulation is, ineffect, 14 CFR Part 119 stripped down to a fewsentences, requiring commercial and non-commercial operators intending to fly unmannedaircraft weighing 20 kg/44 lbs. or more (and somesmaller UAS based on the type of operations andnumber of aircraft involved) to have: A technical (maintenance) and operations or-

ganization appropriate to the intended activity; Qualified pilots; An Operations Manager; A continuing airworthiness program; An operating manual with content as described

above; and

A certificate of airworthiness/permit to flybased on the intended operating configuration.

In addressing model aircraft, the draft regula-

tion defines them in terms of both their weight (less

or greater than 20 kg/44 lbs. maximum takeoff

weight) and, for the small systems, their propulsion

systems. Model aircraft operations are limited to

daylight operations only; must be conducted in

continuous visual contact of the “builder” without

optical or electronic system assistance; pose no risk

to people or property; and be limited to altitudes of

50 meters AGL or below.20 Model aircraft

operations must be covered by liability insurance

and must be conducted using only those portions of

the electromagnetic spectrum authorized for

hobbyist operations.Finally, one passage (Article 21) briefly, simply

and directly addresses a key issue of concern in theUnited States and elsewhere: “Privacy issues arenot within the institutional competence of ENAC.The operator must observe any such regulations inforce.”

42

Appendix 2

Proposed Addition to U.S. Title 14, Code of Federal Regulations

Part 107 – Small Unmanned AircraftSystems

There are two basic approaches to bringing un-manned aircraft into a currently operating aviationsystem:

1. The unmanned aircraft may be required toconform to rules governing existing flightoperations; or

2. The system itself may be required to adjustto the limitations of its unmanned partici-pants.

These two philosophies tend to lead regulatorsin one of two “integration” directions: allow thoseunmanned aircraft that are most capable of operat-ing in the same manner as manned aircraft greateraccess to airspace, or give unmanned aircraft theopportunity for the maximum access to airspacepossible, regardless of their ability to conform toexisting rules governing manned aircraftoperations.

However, in some cases regulatory agenciesare attempting to chart a middle path. For exam-ple, in the winter of 2015, the U.S. Federal Avia-tion Administration (FAA) announced it “hasdecided to proceed incrementally and issue a rulegoverning small UAS operations that pose the leastamount of risk.” To that end, on February 15,2015, the FAA issued for public review and com-ment a “notice of proposed rulemaking” (NPRM)addressing the certification and operation of small(less than 55 pound) unmanned aircraft in U.S. do-mestic airspace. (Readers interested in review theentire document – which runs to nearly 200 pages– should search on-line for it; a link may be availa-ble at www.faa.gov/uas, but this may be takendown at some point.) The NPRM:

Formally establishes a series of UAS-relateddefinitions.

Requires “operator” certificates for sUASpilots as opposed to manned aircraft pilotlicenses/certificates.

Requires registration of all small unmannedaircraft.

Requires sUAS to be “airworthy,” i.e., in asafe condition for flight, but excuses themfrom formal certification processes.

The reasoning behind these broad permissionsincurring “the least amount of risk” is not clearlyexplained in the NPRM’s preamble. However, to a

certain extent a claim of this type can be madebased on the provisions of the proposed rule thattend to keep manned and unmanned operationsclear of each other. For example, the operating al-titude of a small unmanned aircraft is limited to nohigher than 500 feet (150 meters) above groundlevel (§107.51(b)). Section 107.41 imposes limita-tions on sUAS access to certain classes of airspace;a small unmanned aircraft may not operate inClass A airspace, and may not operate in Class B,Class C, or Class D airspace or within the lateralboundaries of the surface area of Class E airspacedesignated for an airport, unless the operator hasprior authorization from the ATC facility havingjurisdiction over that airspace.

Other controls that tend to keep manned andaircraft apart, or to increase the likelihood ofmanned aircraft being able to see small unmannedaircraft in time to avoid them, are provided as well.Right-of-way is addressed by the simple expedientof requiring sUAS to give way to all other aircraft(§107.37); this provision also has the virtue ofavoiding the need to deal with the question of un-manned aircraft designs in different categories(e.g., single-engine, rotorcraft, etc.). Counter-detection concerns are to some extent reduced bylimiting sUAS operations to daytime only(§107.29), under visual meteorological conditionsonly, and §107.51 specifies that sUAS may not ex-ceed 87 knots (100 miles per hour) calibrated air-speed at full power in level flight.

Finally, sUAS weather minima are somewhatmore stringent than those required by 14 CFR§91.155 (“Basic VFR weather minimums”) in someclasses of airspace. The minimum flight visibilityas observed from the location of the ground controlstation must be no less than 3 statute miles (5 kilo-meters); and, the minimum distance of the smallunmanned aircraft from clouds must be no lessthan 500 feet (150 meters) below the cloud and2,000 feet (600 meters) horizontally away from thecloud. (§ 107.51(c) and (d))

By the same token, the proposed rule containssome provisions that are less restrictive than thoseapplicable to manned operations. The safety im-pact of these more relaxed requirements cannot bedetermined due to a lack of relevant safety data orresearch. For example:

§107.9 requires unmanned aircraft opera-

43

tors to report (within ten days of occurrence) acci-dents involving any injury to any person or damageto any property other than the small unmannedaircraft. This is both more and less restrictive than

the corresponding NTSB rule. (49 U.S.C.830.2)

§107.13(d) requires sUAS owners or opera-tors to comply with “all applicable airworthi-ness directives.” However, it is not clear un-der what authority – or by whom – air-worthiness directives could be issued on air-craft lacking production, type or airworthi-ness certificates.

§107.31 requires “the operator or visual ob-server” [emphasis added] to be able to seethe unmanned aircraft throughout the en-tire flight in order to know its location, atti-tude, altitude, and direction; to observe theairspace for other air traffic or hazards; andto ensure that the unmanned aircraft doesnot endanger life or property. However,§107.33 makes the use of a visual observeroptional: “If a visual observer is used duringthe aircraft operation…” [emphasis added].Section 107.31 also relieves pilots in com-mand from the requirement to see their air-craft at all times where an observer is used.

Finally, there are some provisions in the pro-posed rule that address unique aspects of sUAS op-erations. For example, §107.25 prohibits their op-eration from a moving vehicle or aircraft. In ac-knowledgment of the differences between the pur-pose of sUAS operations and those of manned air-craft, §107.49 establishes preflight familiarization,inspection, and other requirements to be accom-plished prior to flight, including:

Assessing the operating environment, considering risks to persons and property in

the immediate vicinity both on the surface andin the air. This assessment must include localweather conditions, local airspace and anyflight restrictions, the location of persons andproperty on the surface, and other groundhazards as appropriate.

Ensuring that all persons involved in the smallunmanned aircraft operation are pre-briefed ontheir roles and responsibilities and potentialhazards;

Verifying that all links between ground stationand the small unmanned aircraft are workingproperly; and

Ensuring that there is enough available powerfor the small unmanned aircraft system to operate for the intended operational time and tooperate after that for at least five minutes.All users of the UAS Guidelines should take

from this example both the challenges associatedwith writing a separate set of rules specific to un-manned aviation and the difficulty of reconcilingsuch rules with those governing existing (i.e.,manned) aircraft operations. This case study alsoshows that enabling UAS access to airspace on an“integrated” basis is easy to set as a goal, but ex-tremely difficult to implement.

Air safety investigators are invited to takenote of potential sources of risk that may resultfrom the compromises that needed to be made inthe various provisions of this proposed rule. Ifmanned and unmanned aircraft are intended to bekept separate as much as possible, but a midair col-lision occurs, two key issues will need to be consid-ered: how the various “segregation” provisionsfailed, and whether the resulting adverse interac-tion between manned and unmanned operationswere preventable with all parties following the re-spective sets of rules established for them.

44

The body of literature associated with unmannedaircraft systems (also referred to as “remotely pi-loted aircraft systems” in some arenas) is large andgrowing on an almost daily basis. A significantamount of popular writing on the subject tends tobe somewhat advocacy-oriented, either pro or con.Air safety investigators looking to expand theirunderstanding of UAS and their issues should notavoid accessible writing of this type, but shouldtreat it with caution.

Similarly, some technical writing on UAS topicscontains an element of advocacy as well. This isunderstandable, since the sector is trying to growand many collective efforts are being exerted tothat end. In the aggregate, government-industrypublications may be considered the most reliablesources of current information, simply because theyare expending the greatest energy in studyingmany of the issues addressed in this document.Again, such sources should not be discountedsimply because of their authorship – they just needto be read with a critical eye and due considerationgiven to what they might leave unsaid on the morecontroversial or difficult-to-manage issues.

The following list is by no means exhaustive. Itwas assembled from suggestions made by ISASIUAS Working Group members from the body ofreference materials with which they were familiar.Where on-line versions are available, the URL isprovided; the Microsoft Word version of the UASInvestigation Guidelines provides links to themthat may be clicked for direct access.

* * * * * *

Concepts of Operations and RoadmapsFederal Aviation Administration, Integra-

tion of Unmanned Aircraft Systems into theNational Airspace System: Concept of Opera-tions, version 2.0 (September 2012) (http://www.suasnews.com/wp-content/uploads/2012/10/FAA-UAS-Conops-Version-2-0-1.pdf)

Federal Aviation Administration, Integra-tion of Civil Unmanned Aircraft Systems(UAS) in the National Airspace System(NAS) Roadmap, First Edition – 2013(http://www.faa.gov/about/initiatives/uas/media/uas_roadmap_2013.pdf)

Joint Planning and Development Office,Unmanned Aircraft Systems (UAS) Compre

hensive Plan: A Report on the Nation’s UASPath Forward, September 2013 (http://

www.faa.gov/about/office_org/headquarters_offices/agi/reports/media/UAS_Comprehensive_Plan.pdf)

National Defense Research Institute, TheRAND Corporation, Applications for NavyUnmanned Aircraft Systems (2010) (http://www.rand.org/pubs/monographs/MG957.html)

U.S. Department of Defense, Unmanned Sys-tems Integrated Roadmap: FY2013-2038(Reference Number: 14-S-0553) (http://www.defense.gov/pubs/DOD-USRM-2013.pdf)

U.S. Air Force, United States Air Force RPAVector: Vision and Enabling Concepts 2013-2038 (February 2014) (http://www.defenseinnovationmarketplace.mil/resources/USAF-RPA_VectorVisionEnablingConcepts2013-2038_ForPublicRelease.pdf)

System Safety and Human FactorsStudies

Chris W. Johnson, DPhil, Department ofComputing Science, University of Glasgow,Scotland, UK and Christine Shea, PhD; ESRTechnology Ltd, Birchwood Park, Warring-ton, Cheshire, UK, “The Hidden HumanFactors in Unmanned Aerial Vehi-cles” (http://www.dcs.gla.ac.uk/~johnson/papers/UAV/Johnson_Shea_UAS.pdf)

Jason S. McCarley and Christopher D.Wickens, University of Illinois at Cham-paign-Urbana, “Human Factors Concernsin UAV Flight” (2004) (https://www.hf.faa.gov/docs/508/docs/uavFY04Planrpt.pdf)

Federal Aviation Administration, Office ofAerospace Medicine, Human Factors Impli-cations of Unmanned Aircraft Accidents:Flight Control Problems, April 2006 (http://www.faa.gov/data_research/research/med_humanfacs/oamtechreports/2000s/media/200608.pdf)

Federal Aviation Administration, Office ofAerospace Medicine, An Assessment of PilotControl Interfaces for Unmanned Aircraft,

APPENDIX 3Recommendations For Further Reading

45

April 2007 (http://www.faa.gov/data_research/research/med_humanfacs/oamtechreports/2000s/media/200708.pdf)

Federal Aviation Administration, Office ofAerospace Medicine, An Investigation ofSensory Information, Levels of Automation,and Piloting Experience on Unmanned AircraftPilot Performance, March 2012 (http://www.trb.org/Main/Blurbs/166911.aspx)

Office of the Under Secretary of Defense forAcquisition, Technology and Logistics, Un-manned Aircraft Systems (UAS) Ground ControlStation Human-Machine Interface (HMI) Devel-opment and Standardization Guide, version 1.0(2012) (https://ucsarchitecture.org/system/files/5/original/UAS_GCS_HMI_Guide_19July2012.pdf?1347481941)

Tobias Nisser and Carl Westin, Lund UniversitySchool of Aviation, Human Factors Challenges inUnmanned Aerial Vehicles (UAVs): A LiteratureReview (2006) (http://www.lusa.lu.se/upload/Trafikflyghogskolan/HumanFactorsChallengesUnmannedAerialVehi-cles.pdf)

United States Air Force, 311th Human SystemsWing, Human Factors Considerations in Migra-tion of Unmanned Aircraft System (UAS) Opera-tor Control (HSW-PE-BR-TR-2006-0002) (http://www.wpafb.af.mil/shared/media/document/afd-090121-046.pdf)

U.S. Army Aeromedical Research Laboratory,The Role of Human Causal Factors in U.S. ArmyUnmanned Aerial Vehicle Accidents, USAARLReport No. 2004-11 (March 2004) (www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA421592)

Rules and Recommended PracticesAustralian Government, Civil Aviation

Safety Authority, CASR Part 101 – Un-manned aircraft and rocket operations(http://www.casa.gov.au/scripts/nc.dll?WCMS:PWA::pc=PARTS101)

International Civil Aviation Organisation,Circular 328 – Unmanned Aircraft Systems(UAS) (http://www.icao.int/Meetings/UAS/Documents/Circular%20328_en.pdf)

Joint Authorities for Rulemaking on Un-manned Systems (JARUS), JARUS-ORG,draft version 0.17 (27 April 2014) (http://jarus-rpas.org/index.php/deliverable/category/11-external-consultation-on-jarus-org)

UK Civil Aviation Authority, CAP 722: Un-manned Aircraft System Operations inUK Airspace – Guidance (http://www.caa.co.uk/docs/33/CAP722.pdf)

U.S. Army, Army Regulation 95-23, Aviation:Unmanned Aircraft System Flight Regula-tions (July 2010) (http://www.apd.army.mil/pdffiles/r95_23.pdf)

Accident and Incident Reports andFormats

National Transportation Safety Board,CHI06MA121, General Atomics Predator-B, Brief of Accident, 04/25/2006 (http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20060509X00531)

Scientific and Technical Information Pro-gram Office, National Aeronautics andSpace Administration (NASA / TM-2007-214539), Preliminary Considerations forClassifying Hazards of Unmanned AircraftSystems, February 2007 (http://shemesh.larc.nasa.gov/people/jmm/NASA-2007-tm214539.pdf)

U.S. Department of the Army, DA Form 2397-U, Unmanned Aircraft System Accident Re-port (UASAR) (https://safety.army.mil/accidentreporting/FORMS/AviationAccidentFormsInstructions/tabid/463/Default.aspx)

Technical Issues (Spectrum, Detect andAvoid, etc.)

Access 5 Project Office, Sense-and-AvoidEquivalent Level of Safety Definition for Un-manned Aircraft Systems (January 2005)(http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080017109.pdf)

EASA.2008.OP.08, Interim Report of the Pre-liminary Impact Assessment on the Safety ofCommunications for Unmanned AircraftSystems (UAS), July 2009 (http://easa.europa.eu/system/files/dfu/UAS_COMMS_Impact%20_asessment_interim_report_V1.pdf)

European Organisation for the Safety ofAir Navigation (EUROCONTROL) CND/CoE/CNS/09-156, Unmanned Aircraft Sys-tems – ATM Collision Avoidance Require-ments (May 2010) (http://www.eurocontrol.int/sites/default/files/content/documents/nm/safety/ACAS/as-unmannedaircraftsystemsatmcollision-avoidancerequirements-2010_.pdf)

International Telecommunications Union– Radiocommunications Sector (ITU-R), Re-port ITU-R M.2171, Characteristics of

46

unmanned aircraft systems and spectrumrequirements to support their safe operationin non-segregated airspace (December 2009)(http://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-M.2171-2009-PDF-E.pdf)

Keven A. Gambold, MAS BSc, GAPAN NorthAmerica, Unmanned Aircraft System Accessto National Airspace (November 2011)(http://www.gapan.org/file/917/uas-access-to-national-airspace-paper.pdf)

END NOTES

1- The term “unmanned aircraft system” showssome signs of being gradually supplanted by theterm “remotely piloted aircraft system” (RPAS).The International Civil Aviation Organization(ICAO) itself seems somewhat divided on thematter. It is true that the remote location of anunmanned aircraft’s pilot is a critical distinctionbetween manned and unmanned operations.However, it is to some extent misleading to labelthe family of aircraft in such a way as to implythat a pilot always is part of their operation. Insome modes of operation – those conducted auton-omously by design, as well as those resultingfrom failures of the electronic link between pilotand aircraft – the nominal pilot in command hasno ability to change the trajectory of the aircraftin any way. Therefore, this document uses theterm “UAS,” although future revisions maychange all such references to “RPAS” if generallyaccepted usage moves in that direction.

2- Chapter 6, related to UAS training for investi-gators, is a high-level discussion of basicknowledge needed. Follow-on work will be neededto translate its observations and recommenda-tions into lesson plans.

3- For an excellent discussion of this issue, seethe Australian Transport Safety Bureau, Limita-tions of the See-and-Avoid Principle (April 1991) -- http://www.skybrary.aero/bookshelf/books/259.pdf.

4- It is only fair to point out that a collision be-tween two unmanned aircraft may be just as pos-sible, and perhaps more so, if the preferredmeans of trying to make UAS operations safe re-lies on airspace segregation that puts multipleunmanned aircraft in a narrowly constrained alti-tude band or geographical location. However, aUAS-on-UAS collision is likely to have far less

impact on the public or in the media than one in-volving loss of life. The latter also would be farmore likely to drive immediate political responsesthat could have a detrimental effect on the scope,or even the viability, of the unmanned aviationsector.

5- To the latter point, it is important to bear inmind that datalink failures could result in theimmediate cessation of performance data flowfrom the aircraft to the GCS. For this reason,some manufacturers incorporate separate on-board flight data recorders similar to those tradi-tionally used aboard aircraft. ICAO is workingtoward a standard set of recommended provisionsto this end.

6-This example in turn suggests issues regardingthe extent to which necessary information can beprovided efficiently and interpreted effectively, aswell as the availability of RF spectrum, band-width, and on-board resources for transmitting it.These are non-trivial issues that barely havebeen addressed as efforts to expand the un-manned aviation sector have gained momentum,and which may not come to the fore until docu-mented in conjunction with accidents and theirensuing investigations.

7- 47 CFR 2.106, Non-Governmental Footnote 46:“In the bands 72–73 and 75.4–76 MHz, the use ofmobile radio remote control of models is on a sec-ondary basis to all other fixed and mobile opera-tions.” Fifty channels (72.0 –73.0 MHz) are availa-ble for model aircraft devices, which must limittheir emissions to a bandwidth of 8 kilohertz(kHz).See generally 47 CFR Part 95.

8- Report ITU-R M.2171 (12/2009), Characteris-tics of unmanned aircraft systems and spectrumrequirements to support their safe operation innon-segregated airspace (M Series: Mobile, radi-odetermination, amateur and related satellitesservices).

9- Uniform use of the code “7400” to designate anunmanned aircraft operating autonomously as aresult of control link failure is being studied bythe FAA and ICAO at this writing.

10- Access 5 materials were preserved by NASAand provide valuable insight into a host of the is-sues referred to throughout these Guidelines; seehttp://web.archive.org/web/20060627203947/www.access5.aero/site_content/index.html.

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11- Similar considerations will need to be ad-dressed in the case of a damaging UA collisionwith a surface structure or feature.

12- Some systems are beginning to be providedwith hybrid control systems that use a combinationof terrestrial communications and conven-tional (non-satellite) radio control of the aircraft.BLOS-equipped aircraft invariably have (usuallyseparate and parallel) LOS capabilities, meaningthat the latter can be employed to effect a safe re-covery if the aircraft is programmed to come intothe range of a suitably equipped GCS followingsatellite- supported link failure.

13- As an example, see Appendix 1 and 2 to see howItaly and the U.S. have addressed these issues.

14- See generally ASTM F2910-14, Standard Speci-fication for Design and Construction of a SmallUnmanned Aircraft System (sUAS), Paragraph 5(“Requirements”).

15- The SCF-NP definition includes the following:“For unmanned aircraft, includes failure or mal-function of ground-based, transmission, or aircraft-based communication systems or components ordatalink systems or components.” The separateDefinitions and Usage Notes document for SCF-NPexpands upon this over-generalized perspective oncontrol link failures; “unanticipated lost commandand control link to a UAS” is prescribed for use asfollows: “To be coded regardless of where the failureoccurred, i.e., on the unmanned aircraft, in the re-mote pilot station (coded with a –RPS suffix), or inthe communication infrastructure between them,whether the communication infrastructure isground, air or space based, or a combination.” It also

explicitly excludes “lost links that are anticipated.”

16- “Remote pilot station” appears to be becomingincreasingly popular in ICAO usage vice the morecommon “ground control station.” Since it is thepreferred term in the CICTT issuances, it isincluded to match other existing references. PerICAO Circular 328, Unmanned Aircraft Systems,Remote Pilot Station (RPS) is defined as “the sta-tion at which the remote pilot manages the flightof an unmanned aircraft”.

17-Historically, most air safety investigators (or atleast investigators-in-charge) have been drawnfrom the ranks of certificated pilots. An operation-al aviation background provides most of theknowledge base needed to effectively understandand investigate unmanned aircraft-involved acci-dents. Nevertheless, first-hand UAS experienceshould be considered either mandatory or highlydesirable for anyone running a UAS-involved in-vestigation. If such cannot be reasonably obtainedin advance of an investigation, the participation ofa subject matter expert specifically qualified in theinvolved system and personally familiar with theground control station arrangement in use duringthe accident sequence should be considered manda-tory.

18- An example of this would be where a require-ment for all UAS to be transponder-equipped, evenfor VFR operations in uncontrolled airspace, subse-quently allowed a UA to be successfully trackedand separated from following CNPC failure.

19- Investigators always should be open to thepossibility that an unexplained manned or un-manned aircraft accident might have been theresult of a midair collision with an unmannedaircraft. The lack of unexplained physical remainsor an unrelated overdue aircraft can make such anevent more difficult to recognize, as can the factthat the operators of smaller systems may not evenbe aware that their aircraft has gone missing dueto a collision if it was not in sight at the time of theevent. The time-tested practice of identifying “toomany parts” in wreckage may be complicated bythe involvement of smaller unmanned aircraft,which might leave less physical evidence of theirpresence but still could have imparted a significantamount of force to a critical component (engine,control surface) or to the cockpit itself.

20- Heavy model aircraft (20 – 150 kg) operationsmust be conducted pursuant to annually renewedauthorization letters from ENAC in designatedareas only (which are treated as “segregated areas”for the purpose of this regulation), but may go up to150 meters AGL and are not subject to propulsionsystem size limits.

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2 – Table of Contents3 – Executive Summary4 – Foreward6 – Preface7 – Chapter 1 – Purpose and Structure of the

Unmanned Aircraft System (UAS) Handbook and Accident/IncidentInvestigation Guidelines

8 – Chapter 2 -- Differences between Manned andUnmanned Aircraft

9 – Key Concepts Underlying Unmanned AircraftSystems

9 – Key Differences between Manned and Unmanned Aircraft

11—Special Aspects of Unmanned Aircraft SystemDifferences

11 – “Detect and Avoid” systems12—Cockpit Design12 – Accidents Where UAS Differences from

Manned Aircraft May Be a Factor12 – Midair Collision14 – Loss of Control Accidents (Airborne)15 – Loss of Control Accidents (Ground) and

Ground Collisions15 – System/Component Failure or Malfunction16 – Chapter 3 – Augmentation and

Supplementation of Existing InvestigativeCapabilities for UAS Investigations

16 – Investigative Skills and Knowledge Associatedwith Unmanned Aircraft System Attributes

16 – Human Factors17 – Telecommunications23 -- Aircraft Structures23 – Electrical Propulsion Systems23 – Pre-Accident Hazard Assessments24 – Considerations for Investigations Involving

Beyond Line of Sight UAS Operations24 – Investigation of Accidents Involving Model

Aircraft26 – Chapter 4 – Annex 13 to the Convention on

International Civil Aviation: Recommenda-tions Relative to UAS Investigations

26 – Recommendation Regarding Determining theState of Occurrence

26 – Special Circumstances Where AdditionalAccredited Representatives May be

Warranted26 – State of Design26 – State of Manufacture26 – Aircraft and Ground Control Station

Registered in Different States

26 – Location of Pilot/Operator Different from Stateof Occurrence

26 – Chapter 5 –Data Fields Associated with UASOperations Requiring Capture

27 – CICTT and UAS27 – ISASI UAS Working Group Position and

Recommendations28 – Chapter 6 – UAS Specific Air Safety

Investigator Skills29 – Chapter 7 – Evidence Preservation Following

Unmanned Aircraft System Accidents29 – On-Scene and Ground Control Station

Investigations29 – Testimony from the Pilot in Command and

Other Crew Members29 – Chapter 8 – UAS Investigation Procedural

and Functional Considerations30 – Near-Term Investigation of UAS Accidents

and Incidents30 – Preliminary Considerations31 – Tailoring Local Guidance to Incorporate UAS-

Related Considerations31 – Areas of Investigation38 – Final Report Content40 – Appendix 1 –Significant Aspects of the Draft

Italian Unmanned Aviation Regulations42—Appendix 2 Proposed Addition to U.S. Title

14, Code of Federal Regulations44 – Appendix 3 – Recommendations for Further

Reading44 – Concepts of Operations and Roadmaps44 – System Safety and Human Factors Studies45 – Rules and Recommended Practices45 – Accident and Incident Reports and Formats45– Technical Issues (Spectrum, Detect and Avoid,

etc.)46 – End Notes48 — Index

INDEX