human systems iac gateway

The Human Systems IAC is a UnitedStates Department of DefenseInformation Analysis Center adminis-tered by the Defense TechnicalInformation Center, Ft. Belvoir, VA,technically managed by the Air ForceResearch Laboratory HumanEffectiveness Directorate, Wright-Patterson Air Force Base, OH, andoperated by Booz Allen Hamilton,Mclean, VA.ht

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iacVolume XII: Number 3 (2001)

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Published by the Human Systems Information Analysis Center, formerly known as CSERIAC

GATEWAYHuman Systems IAC

In the early days of aviation, the vast majori-ty of accidents were the result of mechanicalfailure. As aviation matured and the technol-

ogy improved, more and more mishaps could beassigned to a problem in the human end of theequation. At present, these human problems, orhuman factors, make up the majority of causesof aircraft mishaps. One of the principal humanfactors that are causal in mishaps is spatial dis-orientation (SD).

As shown in Figure 1 (see Page 2), which isdrawn from USAF Safety Center data, the rate ofUSAF SD related mishaps per 100,000 flying hourschanged little from 1991 to 2000. Study of the 20years prior to this time reveals similar numbers.The data from the Army and Navy show similarfindings, as do the FAA figures. For the USAFalone, this adds up to an average of $140 millionannually. As a result of this, both the researchcommunity and operations personnel are workingon methods of improving recognition of SD anddeveloping better SD countermeasures.

The effort to reduce SD mishaps can be brokendown into three general areas: improved trainingmaterials and techniques, development of tech-nologies to minimize the occurrence of SD and

assist in the recovery from SD, andresearch into the physiological mecha-nisms leading to SD. This three-prongedeffort has led to numerous advances inthe understanding of the causes of SDand its inter-relationship with both thecognitive process and the physiologicalmakeup of the human body.

The training effort has looked atdevices for the demonstration of SD onthe ground, and more recently, specificflight profiles to demonstrate SD andinstruct the student in SD countermea-sures. The technological approach hascontributed to SD training devices, buthas had the most impact in the area ofimproved aircraft displays. Theseimproved displays are intended to bemore intuitive and therefore, will hope-fully decrease the likelihood that thepilot will develop SD. Research into thephysiological mechanisms of humanorientation systems has led to increasedunderstanding of the causes and coun-termeasures for SD.

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Glossary of SpatialDisorientation Termsand SpatialDisorientationAcronyms

Measuring the HeadTilt Illusion DuringSustained Acceleration

Canadian Approach toSpatial DisorientationTraining

Calendar

Products

Spatial Disorientation,GeographicDisorientation, Loss ofSituation Awareness,and Controlled Flightinto Terrain

Advanced DisplayTechnologies: WhatHave We Lost?

Desdemona: AdvancedDisorientation Trainer

Major Todd Heinle

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Spatial Disorientation Research

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Internationally, SD is recognized as avery real danger to aviation and as such,many different nations are engaged inresearch activities designed to counterthis threat. The U.S. Air Force ResearchLaboratory (AFRL) has initiated itsSpatial Disorientation Countermeasuresprogram, with research and develop-ment taking place in training, technolo-gy, and the understanding of the physio-logical mechanisms of SD. TheCanadians have implemented a compre-hensive training program for their air-crews. The Dutch are constructing ahighly advanced device designed forboth research and training. TheAustralians are concerned with thepotential increases in SD brought aboutby new display technologies.

This is a complex issue that is extreme-ly costly in lives and equipment. The res-olution will not be easy, nor necessarilyquick, but any reduction in SD mishapscan be considered a success in terms oflives saved and aircraft preserved.

This special issue of GATEWAYincludes five articles that describe someof the SD training research, technologi-cal remedy development, and physio-logical research by many organizations.Collectively, these projects show thebreadth of the recognition of the seri-

ousness of this problem; they are advancing thescience and technology information about SD; andthey increase our expectations that the number ofaccidents will be reduced.�

ReferencesDavenport, C. (2000, November). How much are

we willing to pay?, Spatial DisorientationSymposium. San Antonio, TX.

Estrada, A., (2000, November). Spatial disorienta-tion accidents in U.S. Army rotary wing aircraftFYs 1996-2000, Spatial DisorientationSymposium. San Antonio, TX.

Johnson, K. R., Ph.D. (2000, November). Spatialdisorientation in military aviation, SpatialDisorientation Symposium. San Antonio, TX.

Veronneau, S. J. H., MD (2000, November).Civilian spatial disorientation mishap experi-ence, Spatial Disorientation Symposium. SanAntonio, TX.

For further informationplease contact:

Major Todd Heinle

Tel: (937) 656–7011DSN: 986–7011E-mail: todd.heinle@

wpafb.af.mil.

http://www.spatiald.wpafb.af.mil

Major Todd Heinle is theProgram Manager of AFRL’sSpatial DisorientationCountermeasures Program.

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Human Systems IAC GATEWAY Volume XII: Number 3

Glossary of Spatial Disorientation TermsAutokinesis illusion A dim light in a dark background, when stared at for 6–12 seconds, will give the

illusion of motion (up to 20 degrees/second, and in one or several directions).

Barany Chair A reduced-friction chair that is capable of near constant-velocity turning and is themost widely used ground-based demonstrator for angular SD illusions.

Blackhole approach Caused by a lack of peripheral visual cues when flying an approach to a well-lighted runway at night surrounded by little or no other lighting. Causes pilots tofly lower than normal approaches.

Coriolis illusion An illusion of angular motion (usually pitch or roll) that occurs when the head isremoved from the plane of rotation; this illusion is also known as “cross-coupling”and is frequently associated with nausea, vomiting and other symptoms in naïvesubjects.

Distance-Depth illusion The misperception of distance due to any of a number of visual cues. Generallyassociated with objects that are learned to be a certain distance due to their size,and when a smaller similarly shaped object is seen at the same distance, thesmaller size now makes the object to appear further away.

False horizon illusion Misperception of the actual horizon caused by the presence of sloping terrain onor near the horizon, or strings of lights near the horizon, as on a well-lighted high-way at night.

Flicker Vertigo A confusion of the vestibular system usually associated with strobe lights or alight-flashing sequence between 5 and 20 Hz. Occurs primarily in helicopters.

G-excess illusion An illusion that occurs when a pilot moves his or her head in a >1-G environ-ment, which leads to excessive shearing of the otolith organs and to an exagger-ated sensation of head, body, or aircraft tilt.

Leans A feeling of being banked when the aircraft is actually upright and level; this illu-sion can be caused by both gravitoinertial forces (e.g., leveling out from a pro-longed turn) or by visual factors (e.g., a sloping cloud-deck).

Leans illusion A false perception of the horizontal plane resulting in the individual leaning awayfrom true vertical to compensate.

Runway width illusion A wider or narrower runway than expected by the pilot will give the illusion ofbeing too low, on a wide runway, or too high, on a narrow runway.

Sloping runway illusion The sloping runway gives the pilot the illusion of being too high or too low onapproach, because his visual system has been trained to expect a flat runway.

Somatogyral illusion A false sensation of rotation (or absence of rotation) that results from misper-ceiving the magnitude or direction of an actual rotation. This results from theinability of the semicircular canals to register accurately a prolonged rotation.

Spin recovery illusion Another name for the somatogyral illusion.

Spatial Disorientation AcronymsCFIT Controlled Flight Into Terrain

GD

G-LOC G-induced Loss Of Consciousness

SA Situational Awareness

LSA Loss of Situational Awareness


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120° to follow a point on the ground. Aerial com-bat can frequently require the pilot to look direct-ly behind him (“six-o’clock”).

The G-excess illusion is believed to originate inthe otolith organs of the inner ear. The humanvestibular system is comprised of angular acceler-ation transducers (the semicircular canals) andlongitudinal acceleration transducers (theotoliths). The objective of this research effort wasto determine if the effect of head tilt in a greaterthan 1G environment on perception of attitudecould be demonstrated and quantified using aground based human centrifuge. The Air ForceResearch Lab (AFRL) has done extensive studies ofthe Coriolis illusion caused by sustained accelera-tion in its research centrifuge facility called theDynamic Environment Simulator (DES).

MethodsThe general method for this experiment was to

collect a measure of the subject’s perceived orien-tation while s/he was at a steady state G level andactively accomplishing some known head tilt. Thegreater than 1G environment was produced by aman-rated centrifuge and the head-aiming task wasaccomplished with a visual virtual reality system.

Spatial Disorientation (SD) hasbeen known to adversely affectthe performance of aircraft pilots

even to the degree of disastrous acci-dents. There are many causes of SD,but most causes do not always producedisorientation. One reliable cause ofdisorienting illusions involves movingthe head while exposed to sustainedacceleration. This type of SD is causedby the Coriolis illusion, a false percep-tion of rotation caused by stimulationof the semicircular canals in the ears.While any rapid head movement cancause mild sensation of motion, thesustained acceleration greatly magni-fies the phenomenon. When an aircraftis flying straight and level, it experi-ences the same 1G acceleration thatnormal gravity exerts on us standing onthe surface of the earth. When an air-craft turns, however, the turn causesthe acceleration to increase. A high per-formance aircraft can produce 10Gs, or10 times the normal gravity in a tightturn. If the induced G force is down-ward with respect to our body, we callit Gz; if toward our back, Gx; and if tothe side, Gy.

While in a prolonged coordinatedturn, pilots often must look out of thecockpit to find other aircraft or survey atarget. If the head is tilted with respectto the aircraft, and the aircraft is sus-taining an acceleration greater than 1Gz caused by the banked turn, the pilothas an illusion that the head is tiltedmore than it actually is, causing over-steering when coming out of the turn(see Figure 1). If a “correction” is madefor this erroneous sensation, the pilotcan overbank the aircraft. For example,formation flying may require a pilot tomaintain a gaze up and to one side by45°. During air-to-ground missions,pilots may turn their heads as much as

Measuring the Head Tilt IllusionDuring Sustained Acceleration

Tamara L. Chelette, Ph.D., P.E.Biodynamics and Protection DivisionHuman Effectiveness DirectorateAir Force Research Laboratory

Figure 1. G-Excess effect and formation flying.

Collection of the subject’s perceived orientationwas accomplished using a device invented in-house and known as the Tactile Perceived AttitudeTransducer (TPAT). This device consists of an alu-minum hand plate with a glove suspended on theunderside (see Figure 2). When the subject’s handis inserted into the glove, finger and wristrestraints secure the hand such that the back of thesubject’s hand is firmly affixed to the underside ofthe hand plate. The hand plate is mounted on gim-bals so the orientation of the flat hand can bemeasured by potentiometers.

At the end of the DES centrifuge arm is a “cab”which houses a complete aircraft cockpit. Sitting inthe aircraft seat inside the cab, the subject wore ahead-mounted display with a field of view ofapproximately 90º horizontally and 90º vertically.On this display, the subject saw a computer-gener-ated image similar to Figure 3 (see Page 6). Onepart of the image was a round target that the sub-ject tracked by moving his/her head. The secondelement of the display was the cross-reticle in asquare. Sensors on the helmet allowed its orienta-tion in space to be measured, and the helmet ori-entation adjusted the location of the target disk sothat it appeared to be fixed in space, regardless ofhead motion. The cross-reticle was in a fixed loca-tion, and moved with the helmet.

The amount of head movement was controlledby moving the target away from forward and thesubject followed it with the reticle. After the target

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moved to the prescribed location, itremained stationary and began to blinkfor 12 seconds to allow the vestibularmotion to stabilize. After 12 secondswhen the blinking stopped, the subjectadjusted the angle of horizon on theTPAT with the right hand and signaledcompletion by depressing a triggerswitch with the left hand.

The experimental design had 84 com-binations of independent variables: fourcab pitch angles (–5° down, 0°, 5°, and10° up) and four head pitch angles (–30°down, 0°, 30°, and 45° up), presentedrandomly. The acceleration levels were1.0 (earth-normal), 1.4, 2.0, and 4.0 Gz.The three head yaw conditions were: 0°(forward), 45°, and 90° (right). To keepthe rotation of the centrifuge from con-founding the effects of head pitch andyaw, the seat inside the cab was rotatedto the left the same number of degreesthe subject was rotating the head to theright. In this way, the pitch axis of thehead was maintained in the same planeas the cab axis so that an illusory tiltwould be sensed in the same plane as anactual cab tilt. Each of these was repeat-ed twice by each of the nine subjects(seven male, two female) for a total of1,512 trials.

ResultsTo describe the relationship between

actual and perceived head orientation, anumber of linear and nonlinear model-ing techniques were tried. The G-excessillusion is believed to be the excess tiltsensed beyond that accounted for bythe tilt of the head/neck. Therefore, inpredicting the magnitude of the illusionwe assume the individual has self-knowledge of neck tilt. This must besubtracted from the sensed tilt.

This is represented in the two equa-tions below. Using these models, headposition accounted for a statistically sig-nificant component of the perceivedattitude in both pitch and roll. In the rollaxis, 92 percent of the variation inresponse (ground location perception)was accounted for by head position.Results in the pitch axis were also sig-nificant; however the data fit is not asgood. Only 57 percent of the variationin response can be accounted for fromhead position. The nonlinear term


Figure 2. Virtual world of the research subject.

For further information,please contact:

Tamara L. Chelette, Ph.D.Biomedical EngineerDES FacilityAFRL/HEPABuilding 824, Room 2062800 Q StreetWPAFB, OH 45433–7901

Tel: (937) 255–4096DSN: 785–4096Fax: (937) 266–9687


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ConclusionsThe data and models support the hypothesis that

pitching and yawing the head while in a greaterthan 1G sustained acceleration can lead to a mis-perception of the attitude of the aircraft with respectto the earth. This illusion occurs in the pitch axis ifthe head is forward and translates to the roll axis asthe head is turned toward one shoulder. Subjectsdemonstrated accurate awareness of true vehicle tiltup to 10°, but experienced significant distorting illu-sions of approximately 10° when the head tilted inthe -30° to +45° range up to 4 Gz.

The magnitudes of illusions were greater for high-er degrees of head movement and acceleration.However, physiological evidence of rate sensitiveotolitic cells combined with in-flight evidence thatsupports sensitivity to rate of head movementnecessitates the caveat that actual occurrence of theG-excess illusion may result in significantly largertransient illusory angles.

RecommendationsPilots should be made aware of the possibility and

magnitude of the G-excess effect. Training protocolsshould include the caveat that head pitches cancause erroneous sensations of under or overbankingof their aircraft. Special attention must be paid atlow altitude to avoid disaster. Specifically, anupward head pitch combined with a head yaw intoa turn, as is common in formation flying, can resultin a sensation of underbank and a pitch-up of theaircraft. Intended corrective action actually over-banks the aircraft with a pitch down, causing loss ofaltitude. Downward head pitches during turning, asis common during bombing or strafing runs, cancause a sensation of overbanking. Intended correc-tive action actually underbanks the aircraft, causingaltitude gain that could lead to midair collisionwhen in formation flight.�

ReferencesAnderson, J. H., Blanks, R. H. I., & Precht, W.

(1978). Response Characteristics of SemicircularCanal and Otolith Systems in Cats. I. DynamicResponses of Primary Vestibular Fibers. ExpBrain Research, 32, 400–421.

Chelette, T. L. (1991). Developing a Technique forMeasuring the G-excess Illusion, Human FactorsSociety Test & Eval Tech Grp Newsletter, 6(3),2–6.

Guedry, F. E. & Rupert, A. H. (1991). Steady Stateand Transient G-excess Effects, Aviat Space &Environ Med, 62: 252–253.

Lyons, T. J., Gillingham, K. K., Thomae, C. A., &Alberg, W. B. (1990, October). Low-LevelTurning and Looking Mishaps, Flying Safety.

(G0.25) was selected for the head tiltmodels because it consistently fit thedata better than the other three pro-posed terms for the G-excess effect.

Magnitude of Roll Illusion(in degrees)

Roll illusion = 0.3397 x arcsin{(G0.25– 1) x sin [head pitch] x sin[headyaw]}Pitch illusion = 0.1491 xarcsin{(G0.25 – 1) x sin[head pitch] xcos[head yaw]}


Figure 3. Task as viewed through the virtu-al reality goggles.

emphasis of the demonstration is onrecovery, not the causes or solutions ofdisorientation. Although SD could con-ceivably occur during the recovery, itprobably does not occur very oftenbecause the student expects an unusu-al attitude and has a clearly conceivedset of options in his mind when he isgiven the task to right the aircraft.While ground-based training is helpful,it has been shown that demonstrationsof SD within the actual flight environ-ment are complementary to theground-based training. In-flight demon-stration consists of reinforcement of thelimitation of the orientation senses inflight and the enhancement of aircrewawareness to potential SD situations. Inaddition, in-flight demonstrations alsoprovide the trainee with a series offlight procedures to cope with disori-enting circumstances and illusions.With the assistance of Col. MalcolmBraithwaite (Chief of United KingdomArmy Aviation Medical Corps), an avidproponent of in-flight SD demonstra-tions in the rotary wing, a series of in-flight demonstrations of SD in the heli-copter were introduced to senior flightinstructors at the Griffon OperationalTraining Squadron.

Although various technological meas-ures show promise in combating disori-entation training is the only practicalsolution to enhance SD awareness andcountermeasures that can be achievedwithout delay.�

On Earth, our perception of position, motionand attitude with respect to gravity and theearth’s surface is based on the neural inte-

gration of information from our vision, organ ofbalance, muscle and joint receptors, touch andpressure cues, and hearing. When exposed toflight environments under unfamiliar and chang-ing gravitoinertial forces, information from someof these sensory systems is unreliable; therefore,pilots might experience spatial disorientation (SD).Research and technological initiatives that dealwith SD require a great deal of effort and money toimplement. However, training enhancements,where appropriate, can be more readily achievedand so should be addressed without delay. Thisarticle is a brief summary of SD training in theCanadian Forces.

At the undergraduate pilot level, trainees firstencounter orientation and disorientation trainingduring Basic Pilot Aeromedical Training or duringHigh Altitude Indoctrination at the CanadianForces School of Survival and AeromedicalTraining in Winnipeg. The principal objective is toprovide factual knowledge about spatial orienta-tion and disorientation in flight, in a didactic lec-ture taught by trained aeromedical technicians.Ground based demonstrations of Coriolis illusion,spin recovery and false horizon are conductedusing an unsophisticated flight simulator, theGYRO–IPT (Integrated Physiological Trainer, ETCSouthampton, NJ). After completion of basic jettraining, it is recommended that a comprehensivedemonstration of other illusions should be given.These illusions include: somatogyral, closed loopspin recovery, leans, autokinesis, blackholeapproach, runway width, and up-slope runwayillusions. For the rotary wing, the demonstrationalso includes distance-depth perception, flickervertigo and false horizon at night. For refreshertraining and within an operational flyingsquadron, it is encouraged that SD awarenessshould be raised by having experienced pilots listand discuss recurring SD situations that are specif-ic to that aircraft type.

Traditionally, in-flight training includes thedemonstration of unusual attitude recovery. The

Canadian Approach to Spatial Disorientation Training

For further information, pleasecontact:

Dr. Bob CheungDefence and Civil Institute ofEnvironmental Medicine1133 Sheppard Avenue WestToronto, OntarioCanadaM3M 3B9

Tel: (416) 635–2053Fax: (416) 463–2204E-mail: bob.cheung@

dciem.dnd.ca

Bob Cheung Ph.D. is a seniorlevel Defence Scientist and ProjectLeader of Spatial DisorientationCountermeasures and VestibularStudies at the Defence and CivilInstitute of EnvironmentalMedicine, Defence Research andDevelopment Canada, Departmentof National Defence, Canada andAdjunct Professor of Physiology atthe Department of Physiology,Faculty of Medicine, University ofToronto.

Dr. Bob Cheung

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calendar of events

Reno, NV, USA. December 11–13, 2001National Ergonomics Conferences and ExpositionURL: http://www.ergoexpo.com

A Coruna, Spain. April 15–18, 2002Human Factors and Medicine Panel Symposium On Spatial Disorientation in Military Vehicles:Causes, Consequences and CuresTel: 33 15561 2262, Fax: 33 15561 2298. Open to Partners for Peace (PfP) nations

Montreal, Canada. May 5–9, 2002Aerospace Medical Association Annual Scientific MeetingQueen Elizabeth and Sheraton Hotels. Further details to be posted atURL: http://www.asma.org

Munich, Germany. June 18–20, 2002SAE Digital Human Modeling for Design and Engineering (DHM)Forum Hotel, URL: http://sae.org

Pittsburgh, PA, USA. September 23–27, 2002HFES 46th Annual MeetingPittsburgh Hilton and Towers. URL: http://hfes.org

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Spatial Disorientation,Geographic Disorientation,

Loss of Situation Awareness, andControlled Flight into Terrain

Spatial orientation and disorienta-tion are commonly used terms inneurology and neuropsychology

as well as aviation, and they mean dif-ferent things to different professions.Someone who suffers from brain damageand is spatially disoriented, for example,may have an inability to tell right fromleft, or may have trouble finding theirway around unfamiliar surroundings.This is not what spatial orientation refersto in the aviation environment, however.In the aviation world, spatial orientationmainly refers not to our position relativeto particular places on earth but in rela-tion to earth-fixed space in general.According to its most widely used defini-tion, one that has been accepted by alarge number of countries, spatial disori-entation (SD) refers to:

[A failure] to sense correctly the posi-tion, motion or attitude of the aircraft orof him/herself within the fixed coordi-nate system provided by the surface ofthe earth and the gravitational vertical.(Benson, 1988).

Added to this standard definition isthe caveat that:

… errors in perception by pilots of theirposition, motion or attitude withrespect to their aircraft, or their ownaircraft relative to other aircraft, mayalso be embraced within a broader def-inition of spatial disorientation in flight.(Benson, 1988).

What the above definition implies isthat the inability to maintain one’s ori-entation with respect to particularobjects or places on the ground—e.g.,

landing at the wrong airport or other types of “get-ting lost”—do not fall within the definition of SD.Rather, such incidents would fall under the gener-al category of geographical disorientation. Anotherway to view the distinction between spatial andgeographical disorientation relates to the functionsof the three major types of primary flight instru-ments, as described in Air Force Instruction11–217: control (attitude and enginepower/thrust), performance (altitude, airspeed,heading, vertical velocity, acceleration, angle-of-attack, and turn rate), and navigation instruments(bearing, range, latitude/longitude, time). Spatialorientation is maintained by means of the controland performance instruments, whereas geographi-cal orientation is mostly maintained with referenceto the navigational instruments (Gillingham &Previc, 1993). Although some definitions of SD donot include an erroneous perception of altitude(Navathe & Singh, 1994), misperception of altitudeis clearly SD by the standard definition because itinvolves an erroneous sense of “position…withinthe fixed coordinate system provided by the sur-face of the earth and the gravitational vertical.”

The second part of the definition goes beyond theproblem of orienting in relation to earth-fixed spaceto include the perception of the pilot’s relationshipto his or her own aircraft—as in the “breakoff” andother phenomena in which the pilot may feeldetached and flying from outside the aircraft—aswell as parameters such as separation distance andclosure rate relative to other aircraft. Misperceptionof these latter elements may or may not occur inassociation with other spatial orientation problems,and by no means should all mid-air collisions belisted as SD mishaps. However, some mid-airs mayoccur because the pilot is unaware of his or herown aircraft’s velocity or trajectory in space—i.e., amanifestation of SD. How such SD-related mid-airsmight occur is illustrated by the pilot of the secondaircraft in a formation of two who, after refueling,attempted to maneuver his or her aircraft into astandard formation position behind and above

Bill ErcolineFred Previc

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lead. However, as the pilot established a cutoffangle on lead, while moving away from the tanker,he inadvertently allowed the aircraft to descend.The result was a mid-air collision with number twocolliding with the lead aircraft, where two aircraftand several aircrew members were lost.Investigators were tasked to explain why themishap aircraft would descend into lead. It appearsthe pilot of the mishap aircraft misperceived thelead aircraft as descending, when number two wasactually descending. This occurred when themishap aircraft slowly rolled out of the interceptbank. During the rollout, the pilot of the mishapaircraft misperceived the lead aircraft as descend-ing, when the apparent movement of lead withrespect to the mishap aircraft’s canopy rail causedthe perception of a descending lead. The mishapaircraft was only trying to follow lead. Because ofthis latter definition of SD, the resulting mid-airwould have justifiably been considered an SD-relat-ed mishap. As might be expected, broadening thecategory of SD mishaps to include disorientationrelative to other aircraft results in a large increasein the SD mishap rate (Neubauer, 2000).

What is termed SD today was not alwaysreferred as such. Until the 1970s, SD was alsoreferred to as “aviator’s vertigo” or “pilot vertigo,”while spatial orientation was often referred to as“aerial equilibrium.” The term “spatial orienta-tion” appeared in a classic early text on instrumentflight (Ocker & Crane, 1932), and the term “spatialdisorientation” was used shortly thereafter(Macurdy, 1934). Although SD was a commonlyused term by the 1950s, “vertigo” was still includ-ed in place of SD in aerospace medical textbooksuntil 1971 and in United States Air Force (USAF)mishap forms until 1989. Today, “vertigo” is rec-ognized as a separate symptom—usually referringto dizziness, light-headedness (“giddiness” in theolder literature), visual-field instability, or otherphysical or emotional sensations produced by themotions of flight—whereas SD is recognized as aphenomenon that can occur with or without suchsensations. Indeed, all too many pilots have goneto their death never feeling or suspecting that any-thing was amiss with their aircraft’s altitude or tra-jectory. What may be experienced during one typeof SD may be very different than what is experi-enced during a different type, which begs thequestion as to the different types of SD.

There are three accepted types of SD—unrecog-nized, recognized, and incapacitation. Type I SD(unrecognized) is the most common and is usual-ly associated with subthreshold motion, incom-plete or failed instrument crosscheck, task satura-tion, or channelized attention. Type II SD (recog-nized) is the more traditional type of disorienta-tion. It is associated with known conflicts between

two or more of the sensory mechanismsrelated to spatial orientation (e.g.,degraded vision and semicircular canalstimulation). The third type of SD (TypeIII) is known as incapacitating. This SDis the least known and least under-stood. It appears that under certainconditions the pilot of an aircraft canbecome so engrossed in a task thatapparent stick inputs have no effect onaircraft control. The pilot is aware of theconflict, is physically trying to correctfor it, but is unable to make the aircraftrespond appropriately. Research has yetto quantify the causes of this type of SD.

Another related term that becamewidely used in the 1980s and 1990s isloss of situation awareness (LSA). Thisterm, which dates back to World War II,was the subject of little research interestuntil the 1980s. It is a more general termthan SD, as it refers to the loss of apilot’s “perception of the elements inthe [aviation] environment within a vol-ume of time and space, the comprehen-sion of their meaning, and the projec-tion of their status in the near future”(Endsley, 1993). Because spatial orien-tation is undoubtedly a “key element inthe aviation environment,” spatial ori-entation is generally considered to be asubset of situation awareness(Gillingham, 1992; Previc, Yauch,DeVilbiss, Ercoline, & Sipes, 1995).Thus, any pilot suffering from SD alsohas LSA, although the reverse is notalways true—e.g., a military pilot maylose his or her tactical sense and sufferfrom the threat of being shot down(and, by definition, LSA) without losingspatial orientation. Nevertheless, non-SD components of LSA can often pre-cipitate SD, because the task of regain-ing LSA may divert the pilot’s attention-al resources and lead to a failure toproperly crosscheck the flight instru-ments. The relationship between spatialorientation and situation awareness isshown in Figure 1 (see Page 12).

A final term that has been used inconjunction with SD is controlled-flight-into-terrain (CFIT) (Scott, 1996). Whilethe vast majority of CFIT accidentsinvolve a misjudgment of altitude (oftenduring landing) and therefore should beclassified as SD, some may be classifiedas geographical disorientation. If, for



Bill ErcolineVeridian Engineering8111 18th StreetBrooks AFB, TX78235–5215

DSN: 240–5465E-mail: bill.ercoline@

brooks.af.mil

Fred Previc, Ph.D.Senior Member of theTechnical StaffNorthup GrummanInformation Technology4241 Wookcock Drive, Suite B–100San Antonio, TX 78228

Tel: (210) 536–4779Fax: (210) 534–0420E-mail: fred.previc@

brooks.af.mil


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Endsley, M. R. (1995). Toward a theory of situa-tion awareness in dynamic systems. HumanFactors, 37, 32–64.

Gillingham, K. K. (1992). The spatial disorienta-tion problem in the United States Air Force.Journal of Vestibular Research, 2, 297–306.

Gillingham, K. K., & Previc, F. H. (1996). Spatialorientation in flight. In R. L. DeHart (Ed.),Fundamentals of aerospace medicine (2nd Ed.)(pp. 309–397). Baltimore: Williams & Wilkins.

Macurdy, J. T., (1934). Disorientation and vertigo,with special reference to aviation. BritishJournal of Psychology, 25, 42–54.

Navathe, P. D., & Singh, B. (1994). An opera-tional definition for spatial disorientation.Aviation, Space, and Environmental Medicine,65, 1153–1155.

Neubauer, J. C. (2000). Classifying spatial disori-entation mishaps using different definitions.IEEE Engineering in Medicine and Biology,19(2), 28–34.

Ocker, W. C., & Crane, C. J. (1932). Blind flight intheory and practice. San Antonio, TX: Naylor.

Previc, F. H., Yauch, D. W., DeVilbiss, C. A.,Ercoline, W. R., & Sipes, W. E. (1995). Indefense of traditional views of spatial disorien-tation and loss of situation awareness: A replyto Navathe and Singh’s “An operational defini-tion of spatial disorientation.” Aviation, Space,and Environmental Medicine, 66, 1103–1106.

Scott, W. B. (1996). New research identifies caus-es of CFIT. Aviation Week and SpaceTechnology, 144(25), 70–71.

example, a pilot maintains adequate ter-rain clearance for a particular set of geo-graphical coordinates that differ fromthose the aircraft is actually flying over,the pilot may not be aware of impend-ing mountains, power lines, etc. Also,CFIT accidents typically occur duringonly one particular type of SD (Type I),in which the pilot is unaware of his orher misjudgment of terrain clearance,whereas in many SD situations the pilotmay be fighting to maintain control ofthe aircraft before impacting the ground(Types II and III SD).

The thing to remember is that SD canbe masked by several other names. Ifwe are ever to reduce the number ofhuman-error related mishaps, we mustunderstand the reasons these eventsoccur and focus our attention andresources on the causes and counter-measures. SD, GD, LSA, and CFIT areall related to misperceptions of flight. Ithas only been within the last decadethat researchers have been able to con-vince the flying community of the seri-ousness of all these insidious killers.�

ReferencesBenson, A. (1978). Spatial disorienta-

tion—common illusions. In G.Dhenin (Ed.), Aviation medicine:Physiology and human factors.London, U.K.: Tri-Med.


Ownship Info

Tactical Arena

Weather Spatial Orientation

Navigation

Figure 1. An illustration of the relationship between spatial orientation and situation awareness. Inthis scheme, spatial orientation is a subset of situation awareness. (Adapted from Previc et al.,1995).

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opposite of that which is intended.Rather than reducing the operator’sworkload, advanced information dis-play systems have a potential to pro-duce an overload of information. Atpresent DSTO is a partner in a collabo-ration under a Memorandum ofUnderstanding between the French andAustralian governments to investigatedisplay and control technologies in asimulated combat mission environ-ment. The object of the collaboration isto understand the outcomes of address-ing information to the different sensorymodes and enabling inanimate on-board systems to respond to voice com-mands of the pilot. The objective of thisis the evolution of some general princi-ples for design and implementation ofsuch systems in the next generationcombat aircraft.

Data FusionThe potential for loss of situation

awareness may be further exacerbatedby data fusion. In the examples above,the nurse has access to raw data in theform of heart, respiration rates, and soon, and the sonar operator has raw datain the form of sonar returns. Data fusionformats, on the other hand, are likely toenable the operator little or perhaps noaccess to raw data. A fused-data situa-tion display showing an entity—say, athreat—may have difficulty attachingany indication of the “trustworthiness”to what it is indicating. We have con-ducted structured interviews with tacti-cal operators, who reveal that they seekverification of information indicated bysensor signals in the nature and behav-ior of those signals over time. Fused-data formats are ill adapted to this.Even with the application of “smart”enhancements it is difficult to imagine a

James W. MeehanDefence Science and Technology OrganizationMelbourne, Australia

The “Holy Grail” for designers of informationdisplays—particularly aircraft cockpit dis-plays—is maintenance of situation aware-

ness. Spatial disorientation is an element that mil-itates against good situation awareness. Rapidadvance in technology permits us now to deliverinformation to the human operator by almost anysensory mode, potentially in layers of complexity,but understanding of the impact of this on humanperformance lags. While the intention of designersof advanced displays is to reduce elements such asspatial disorientation and operator workload, it isnot clear that this will necessarily be the outcome.

With conventional information displays theexperienced operator can often part-process seg-ments of an information array by recognizing pat-terns in the raw data being presented. This can beseen, for example, in the behavior of a nurse in asurgical recovery room who monitors the patient’svital signs, or a submarine sonar operator scan-ning for targets. Experienced operators can recog-nize patterns in arrays of raw data that indicate a“normal” state or a state that requires a response.This gives rise to a question about what has beenlost in advanced information displays that use newand very different concepts and methods.

Workload: Reduction or Overload?Head-up displays (HUDs) and helmet-mounted

displays (HMDs) are capable of putting visualsymbology in the line of sight of the operator, andadvanced auditory displays can position a largearray of different sounds virtually anywhere inspace. In addition, techniques now enable voicecommunication between the operator and inani-mate systems. There is quite a lot of experimentaldata on line-of-sight visual displays, a growingamount of data on spatial and other auditory dis-plays, and some data are beginning to emerge ondirect-voice recognition systems. However, wehave no data yet on how all this works together. Aclear possibility is that poorly configured informa-tion delivery systems will produce a result that is

Advanced Display Technologies:What Have We Lost?


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means by which such dimensions ofinformation might be reconstituted in adisplay. For example, a ground-to-airthreat indicated in the cockpit of a strikeaircraft, received from an AEW&C plat-form, may in turn be received fromanother platform that is airborne, atsea, or on the ground. It may be that thesource of the original signal is informa-tive to the strike aircrew, but that thisinformation is lost in the fusion. It ispossible to imagine many other charac-teristics of raw data that potentially willbe lost in fusion.

This problem is already recognized byoperators pondering fused-data presen-tation systems. It is likely that datafusion technology will sometimes notpermit reversion to raw data. The chal-lenge is to devise means of restoring tofused-data displays information that cango some way towards compensating forthe loss of information afforded byaccess to raw data.

Attentional CaptureAnother clearly unwanted outcome of

line-of-sight displays is their potential toact as an attentional “trap.” The term“cognitive capture” has been used todescribe this well-recognized androbust phenomenon, but we prefer theterm “attentional capture” as it includescases that are not adequately describedas cognitive (Stuart, McAnally andMeehan, 2001a). Attentional capture isthought to be involved in someinstances of spatial disorientation relat-ed to controlled-flight-into-terrain acci-dents. Pilots are trained to scan visuallyto maintain situation awareness andalso because this can reduce attentionalfixedness following a period of fixed-ness of gaze. However, whereas thepilot can look away from line-of-sightsymbology that is presented in a head-up display (HUD), this is not possiblewith helmet-mounted display symbolo-gy—except in the case of symbologypresented at a fixed location in virtualspace. Certainly symbology can bedeleted with a de-clutter function, butthis is analogous to merely switching offdistracting auditory communications; itcan assist recovery from attentional cap-ture, but may do nothing positive tosupport situation awareness.

We have shown in laboratory experiments thatthe way visual symbology is displayed can signifi-cantly influence response time to stimuli overlaidby the symbology (Stuart, McAnally, and Meehan,2001b). This paradigm is an abstraction of theHUD/HMD situation. High-contrast overlaid sym-bology can impose a cost in response time.Experienced pilots customarily turn the brightnessof the HUD up or down as appropriate so that sym-bology is comfortably visible in ambient condi-tions, indicating that they are already aware of thisintuitively. The way symbology is written can alsopotentially affect human performance adversely. Ithas been shown that verisimilitude of HUD sym-bology with salient ground features will leadunalerted aircrew to fail to detect an importantevent that is clearly visible. Other aspects of sym-bology such as implied direction or other semanticcontent also present a potential for unintendedand unwanted effects.

These matters should be of particular concernto aircrew in combat aircraft—both fast jets androtorcraft—that operate close to terrain, and thoseinvolved in operations and training the aircrew toperform them. More research is required into thebasic processes invoked by new display tech-niques that can result in effects the opposite ofthat which is intended. Identifiable perceptualand cognitive processes are involved, andresearch into these processes should also have arobust theoretical foundation.�

ReferencesStuart, G. W., McAnally, K. I. & Meehan, J. W.

(2001a). Head-up displays and visual attention:Integrating data and theory. Human Factors andAerospace Safety, 1(2), 103–124.

Stuart, G. W., McAnally, K. I. & Meehan, J. W.(2001b). Visual perception and attention in thedesign of head-up and helmet-mounteddisplays. Manuscript in preparation.

For further informationplease contact:

James W. Meehan Ph.D.DSTO Air OperationsDivision506 Lorimer StreetFishermans Bend, VIC 3207Australia

E-mail: [email protected]

James Meehan is SeniorResearch Scientist at theAeronautical and MaritimeResearch Laboratory inMelbourne. His research areais human perception and cog-nition, with a special interestin applications in medicaland aerospace systems, par-ticularly advanced cockpitdisplays.


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form motion, without the angular accel-erations encountered in centrifuges dur-ing the G-onset.

All these motions make Desdemona avaluable tool for research on thevestibular and cardiovascular conse-quences of (super) agile aircraft maneu-vers. Desdemona is also an idealresearch tool to determine to whatextent the Desdemona concept can beused as a flight simulator for fighter air-craft, as a driving simulator, a helicoptersimulator, etc. Desdemona should proveto be superior over standard hexapodmotion platforms when sustained G-loading is required (for driving simula-tion: braking and accelerating, drivingwinding roads, making lane changes.For flight simulation training: take-offand landing, especially from a carrier,and unusual attitude recovery, highlymaneuverable flight profiles, etc.).�

Desdemona is a sophisticated demonstration,simulation and training facility specified byToegepast Natuurwetenschappelijk

Onderzoek (TNO) Human Factors and developedby AMST Systemtechnik (Austria). Desdemona isplanned to be operational in 2003 at the TNOHuman Factors facility in Soesterberg, theNetherlands, for basic and advanced disorientationtraining courses for the benefit of the RoyalNetherlands Air Force (RNLAF).

At present all student aviators from the RNLAFfollow basic spatial disorientation (SD) training atTNO Human Factors where they passively experi-ence the limitations of their vestibular and visualsensory systems on the different research tools.The Desdemona concept was developed to extendthat course to the flight environment with theman-in-the-loop, but still with the ability todemonstrate all vestibular and visual illusions asoccur in flight without cheating.

Consequently, Desdemona Soesterberg isdesigned to offer the motion profiles required forthe basic disorientation course such as unlimitedrotation and prolonged >1g motion profiles. Thisis accomplished by unrestricted rotation of a fullygimbaled cockpit (max yaw, pitch and roll angu-lar accelerations 90°/s2) and by rotation of thetrack, which allows centrifugation up to 3g if thecockpit is in an outer position (see Figure 1).Realistic environment with state-of-the-art visualsand aircraft specific instruments is available in thecockpit, including night-vision. This, togetherwith the vertical motion (the gimbaled cockpitmay move 2m along a straight vertical guide) andthe horizontal motion (the gimbaled cockpit andthe vertical guide may move 8m over the horizon-tal track), both with maximal accelerations of0.5g, allows for semi man-in-the-loop simulationin the refresher course.

Proper combination of the 6 degrees of freedom(DOF) makes Desdemona also a dynamic flightsimulator. Desdemona may replicate the motionenvelopes of a conventional Stewart platform anda gimbaled centrifuge. By the horizontal motionover the track, the Desdemona concept adds a sus-tainable G-load to the conventional Stewart plat-

Desdemona: Advanced Disorientation Trainer

Figure 1. The Desdemona concept: Basic vestibular and visual disorientingillusions to be demonstrated with the pilot in control.

Dr. Willem Bles


Dr. Willem BlesTNO Human FactorsP.O. Box 23 3769 ZGSoesterberg,The Netherlands

E-mail: [email protected]

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