the human element in ageing aircraft...

The Human Element in Ageing Aircraft Safety

A paper for Safeskies 2011, Canberra, Australia, 27th October 2011Steve Swift, Director, Steve Swift Pty Ltd, Canberra, Australia

AbstractNow that the engineering is mature, the main challenge for ageing aircraft safety is the human element. This paper discusses clarity, simplicity and trickery.

IntroductionSafety experts talk about the human element and ageing aircraft, but not often together. Should we?

...takeoff...

In 1977, two Boeing 747s collided at Tenerife airport, killing 583. Causal was a human element: communication [1,2]. From crashes like this, we teach it for the cockpit and tower.

Federal AviationAdministration

Maintenance Human Factors – Maintenance Accidents

• Beech 1900D

• Forward elevator trim control cable replacement

• Reversed elevator trim

• Diagram in maintenance manual depicts reversed trim cable drum

• Failure to perform functional test

• Flight symptoms mimic runaway trim

Colgan Air Elevator Trim Mis-rigging

In 2003, a Beech 1900D crashed soon after takeoff in the USA, killing two. Again, one cause was the human element of communication [3]. From crashes like this, we teach it for maintenance.

Communication and other human elements are important for safety. Are there special issues for ageing aircraft? Let us look under three headings:• clarity• simplicity• trickery.

ClarityI learned the importance of clarity early in my engineering career, while at university. I was designing a wing for my thesis. Another student was stressing it. He told me how long to make part of the main spar. He told me the semi-span. I thought he meant the full span. So my part was too short by half. When we tested it for strength, it broke early and dramatically...

Fortunately I had an understanding professor.

I learned more about the importance of clarity in 2000, when Ansett had to ground several 767s because they had overlooked new inspections Boeing added to the maintenance manual. Boeing described the revision as a “reassessment of the ’50-series’ inspections”. Ansett thought ‘50-series’ meant 50,000 flights, which none of their 767s were near. So, they put the revision aside. But ‘50-series’ meant something else to Boeing. They wanted some of the new inspections to start at 25,000 flights, which several of Ansett’s 767s had passed.

When Ansett realised, not until three years later, they had to inspect and repair the overdue 767s immediately. It stranded passengers and ruined the airline. You can read the full story in [4].

’50 series’: innocent jargon that was unsafe because it was unclear.

In a paper for ICAF 2011, I discuss other ‘ageing aircraft’ words that could be unsafe because they are unclear [5]. One is the word ‘ageing’ itself. The first problem is definition. For the FAA, ‘ageing’ starts from 15 years. For the Civil Aviation Safety Authority (CASA), it starts from ‘the day they leave the factory’ [6]. Supporting CASA is Airbus finding fatigue cracks in the A380 during flight test (see EASA AD 2008-0216). Even the newest and best are ‘ageing’. As CASA says, ‘every aircraft therefore is an ageing aircraft’.

The Human Element in Ageing Aircraft Safety© Steve Swift Pty Ltd 2011

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If so, the word is only useful politically. If it gets more government attention because it is newer and catchier than ‘continuing airworthiness’, the traditional name for the same discipline, then it could be an example of engineers understanding and exploiting the human element for good. Could there be risks? There could if we think it really is new. And, if we think it really is a continuum.

First, false newness. ‘Ageing aircraft’ programs are mainly only retrospective application of new rules, such as those for Instructions for Continued Airworthiness (ICA), to old aircraft. (I mean the ICA in the FARs, which includes a safety standard, not the one in the CASRs, which does not. It would help clarity and safety if CASA could fix this anomaly.) We just need more retrospective application, so all old aircraft have ICAs, not just large airliners. The engineering is mature and ready. We just need to work on the economics and the politics (the human elements).

Second, false continuum. If you were a doctor, you would want to know where a woman was with respect to puberty, pregnancy and menopause. If you were a dentist, you would want to know if you are dealing with a baby tooth, an adult tooth or a false tooth. If you were a financial planner, you would want to know if your client is a student, a worker or a retiree.

But what if you are maintenance planner? Are there milestones for maintenance? An important one is the Limit of Validity (LOV) for the ICA. See FARs 23, 25 and 26.

I C AExpires:

Hours/Flights

L 0 V

When aircraft designers predict risks, they don’t predict them forever. For example, for metal fatigue, they only run the test for a finite time. So, really, ICAs are only good for a finite time, which the FAA calls the Limit of Validity (LOV). The FAA’s Bob Eastin thinks of it as the ‘knowledge horizon’ [7]. Past the LOV, the ICA can no longer assure safety because we don’t know the risks. It is when CASA says the aircraft has ‘outlasted the maintenance system’ [6], and the FAA warns there could be ‘widespread fatigue damage’ (WFD).

A320s are approaching their LOV. So Airbus is running a new and longer fatigue test. In Australia a few years ago, several Cessna 441 Conquests passed their LOV. CASA had to ground them.

In Australia, some aircraft have no ICA. Others have an ICA but no LOV. Neither group’s maintenance can assure safety. If CASA were to fix that, as previously suggested, operators would know when, where and how to ‘take a closer look’ [6]. And, where no ‘look’ could ever be good enough to find deterioration before it is dangerous [8].

If you are an operator looking for assurance, ask your aircraft’s Type Certificate Holder if the maintenance program meets the standard for ICAs (or similar), and has an LOV.

I am not the only one who sees problems with ‘ageing’. For example, the former Ageing Aircraft conferences in the US and Australia now have new names.

Other unclear names are these two:

Airworthiness Limitations

Supplemental Inspections

Pre- LOV = Assurance Post- LOV = Uncertainty


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They are the same maintenance to the same standard. Both are essential for safety. But, while operators revere Airworthiness Limitations, they often ignore Supplemental Inspections because they think ‘supplemental’ means ‘optional’. Non-compliance has been a particular problem for the Supplemental Inspections for Cessna’s piston twins. If they are the same, why don’t we call them the same?

Another term is ‘failsafe’. For years, it deceived us into thinking we no longer needed inspections. It took a crash (707, Lusaka, 1977) and a courageous authority (British CAA, Airworthiness Notice No. 89, 1978) to convince us that even failsafe aircraft need ICAs . Unfortunately, the FAA still allows failsafe for FAR 23 aircraft.

We replaced failsafe with ‘damage tolerance’. Two early ‘damage tolerant’ aircraft were the Airbus A320 and Boeing 757.‘Damage tolerance’ is a good concept with a bad name. Civil and military meanings differ. It confuses ex-military engineers designing civil aircraft, so they ignore inspectability. And, it confuses FAA regulatory policy. Bob Eastin, its Chief Scientific and Technical Adviser on Fatigue and Damage Tolerance, wrote that ‘the use of the same words for different things can lead to confusion and needless debate’ [9].

Also, like fail-safe, damage tolerance fosters complacency. Some think damage tolerant aircraft do not need inspection, or even repair. Some, like DSTO and our Air Force, prefer the term ‘safety by inspection’ (SBI). But, MSG-3 recommends something simpler: just ‘inspection’ [10].

For other unclear words, please refer [5].

Clarity is part of ergonomics. It is cognitive ergonomics instead of physical ergonomics. It is part of ICAO’s SHELL model [11]:

LLIVEWARE

SSOFTWARE

LLIVEWARE

HHARDWARE

EENVIRONMENT

It is important for writing (liveware-software) and speech (liveware-liveware).

Clarity is why the Australian government has a guide on plain English [12]. And, Michèle Asprey a book for lawyers [13]. In 2011, the Commonwealth Ombudsman estimated plain English would reduce complaints about the tax office by two-thirds.

Clarity is why US President Clinton wanted plain English for his government [14] and the FAA has a guide [15]. And why the Europeans wrote ASD-STE-100 for Simplified Technical English [16]. But, a search on CASA’s web site could not find any general policy on plain English.


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SimplicityA help for clarity is simplicity.

Do you remember when complexity in the cockpit was impressive? Like this early DC9 on the left:

But we matured. We learned that complexity increases error. So we now strive for simplicity, like the later DC9 (717) on the right. How much do we strive for simplicity with maintenance documents? Where are their ergonomic standards? Don’t maintainers also have to absorb a lot of information quickly, for safety?

ALS MRBR

SB SID

MPD AD

AMP CAMP

RAP ICAAMM SAIB

CMR CPCP CAP AWB

Sadly, maintenance documents are still like an old cluttered cockpit, especially for old aircraft types. The maintainer must scan too many ‘instruments’ to see everything they have to do. Even in the US Air Force, more standardised than civil aviation, a recent report concluded that the ‘root causes’ for ‘inspection misses’ include ‘confusing...documents and instructions’ [17]. ICAO warns that ‘delays and errors may occur while seeking vital information from confusing, misleading or excessively cluttered documentation and charts’ [11].

It is still too easy to miss or misread an instruction, just as Ansett did ten years ago with the 767. It could happen again with others, like Australian operators of the Beech Queen Air 65-B80. If you want to know the maintenance for fatigue and corrosion in the wing, and you are in the USA, where the Queen Air was designed and built, it is easy. There is an FAA Airworthiness Directive (AD 89-25-08) that says to maintain the wing to the Beech manual (called the Structural Inspection and Repair Manual). Simple.

Other countries, including Europe, refer to the same FAA AD. Again, it is simple.


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COMMONWEALTH OF AUSTRALIA

(Civil Aviation Regulations 1998), PART 39 - 105

CIVIL AVIATION SAFETY AUTHORITY

SCHEDULE OF AIRWORTHINESS DIRECTIVES

Beechcraft 65 and 70 (Queen Air) Series Aeroplanes

AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/BEECH 65/22 Amdt

3 and issues the following AD under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the

delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in

the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned

in the compliance section.

AD/BEECH 65/22

Amdt 4

Wing Spar and Lower Attachment Fittings

11/2000

Applicability:

All models.

Requirement: 1. Remove the wing main spar lower attachment bolts in

accordance with the

manufacturer’s instructions. Strip all paint fro

m the “bath tub” portion of the four

outer wing to centre section main spar lower attachment fittings.

2. Perform a fluorescent liquid penetrant inspection of all fo

ur fittings in accordance

with the Beechcraft Structural Inspection and Repair Manual (SIRM) P/N 98-

39006B3 as revised May 28 1999, Chapter 57-11-00 for models 65, 70 & 80, and

Chapter 57-12-00 for the model 88, Chart 201, Index Nos. 1 and 10 (Note: the

model designations used in the SIRM are the manufacturer’s popular or marketing

designations). When inspecting the “bathtub” portion of the fitti

ngs, pay particular

attention to the bolt counterbore and fillet radius. A

s an alternative, this inspection

may be performed using an eddy current (pencil probe) procedure as detailed in

Chapter 20-00-00 of the SIRM.

In accordance with the SIRM, if a fitti

ng fatigue crack is found, the complete outer

wing main spar lower cap assembly must be replaced in before further flight.

Note 1: The SIRM Chapter 20-00-00 “Warning” regarding not removing paint

should be disregarded. To prevent corrosion, some form of protective treatment, such

as a standard zinc chromate primer, should be applied between inspections, to

surfaces from which the paint has been removed.

Note 2: Solvent removers should be used wherever possib

le. If the use of other paint

strippers is

unavoidable, the complete removal of residue must be ensured before

inspection. In either case, the use of mechanical or abrasive means of paint removal

must be avoided.

Note 3: It is re

commended that the penetrant be applied to the counterbore radius

using a fine artist’s paint brush. This w

ill simplify penetrant removal and minimise

false indications. Care should be taken to ensure full coverage of the fille

t radius and

a similar distance (at least 5 mm) into the cylindrical portion of the counterbore, in

particular on the side of the hole adjacent to the “bottom of the bathtub”.

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105





For the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/BEECH 65/34 Amdt





AD/BEECH 65/34

Amdt 5

Upper and Lower Outboard Wing

Front Spar Caps

11/2000

Applicability: All models.

Requirement: Action in accordance with “Outboard Wing Main Spar Crack and Corrosion

Inspection” in the Beechcraft Structural Inspection and Repair Manual 98-39006B3 as

revised 28 May 1999, Chapter 57-11-00, Figure 208.

Compliance: Prior to exceeding 5 years from the date of manufacture, and thereafter at intervals

not exceeding 1 year.

Note: Aircraft already inspected in accordance with the preceding issue of this

Directive satisfy the initial inspection requirement of this issue.

This Amendment becomes effective on 2 November 2000.

Background: The original AD addressed corrosion and related cracking in the upper and lower

main spar caps and was based on Beechcraft SI 0514-035. Amendment 1 resulted

from Revision 1 to the SI. Amendment 2 consolidated the Beech 65 and 70 series

ADs. Amendment 3 incorporated the use of the inspection method outlined in the

Beechcraft Structural Inspection and Repair Manual, which superseded the SI.

Amendment 4 clarified the Requirement as a corrosion inspection.

This Amendment results from a review of airframe ADs for the Beech heavy twin

engine models, and updates the SIRM reference to the current issue.

Amendment 4 of this Airworthiness Directive became effective on 1 November 1990.

Amendment 3 of this Airworthiness Directive became effective on 7 July 1990

David Alan Villiers

Delegate of the Civil Aviation Safety Authority

13 September 2000

The above AD is notified in the Commonwealth of Australia Gazette on 4 October 2000.

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Beechcraft 65 and 70 (Queen Air) Series Aeroplanes

AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/BEECH 65/57 Amdt





AD/BEECH 65/57 Amdt 4 Wing Panel to Centre Section Attachment - Steel Bolts and Nuts 11/2000

Applicability: All models. Requirement: 1. Remove and carry out inspections of all eight wing attach steel bolts and nuts in accordance with the procedures outlined in the Beechcraft Structural Inspection and Repair Manual 98-39006B3 as revised 28 May 1999, Chapter 57-11-00 for models 65, 70 & 80, and Chapter 57-12-00 for the model 88, Chart 201 Index No. 10, “Wing bolt, nut, and spar fitting inspection”.

2. Renew all eight wing attach bolts and nuts. Note: Inspection of the wing attach fittings is detailed in the current issue of AD/BEECH 65/22. Compliance: For Requirement 1. Prior to exceeding 2 calendar years since bolt and nut installation, and thereafter at intervals not exceeding 2 calendar years. For Requirement 2. At intervals not exceeding 6 calendar years since installation. This Amendment becomes effective on 2 November 2000. Background: The original issue of this AD became effective on 6 November 1981. It was distributed by Telex and was based on FAA AD 81-23-01. It followed an in-flight failure of a steel bolt in the USA and required inspection of the forward upper and lower bolts, nuts and fittings.

Amendment 1 promulgated Beech SI 1208, which extended the inspection to all bolts, and introduced repetitive inspections. Amendment 2 became effective on 22 March 1989, and consolidated the Beech 65 and 70 series AD schedules. Amendment 3 became effective on 6 September 1990. It promulgated the Beechcraft Structural Inspection and Repair Manual, which superseded SI 1208. The Note referring to AD/BEECH 65/65, Model 65-B80 bolt torque was also introduced.

COMMONWEALTH OF AUSTRALIA

(Civil Aviation Safety Regulations 1998), PART 39.001(1)



Page 1 of 4


On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes

Airworthiness Directive (AD) AD/BEECH 65/64 and issues the following AD under subregulation 39.001(1) of CASR 1998. The AD requires that the action set out

in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical

product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the

requirement section; and (c) at the time mentioned in the compliance section.


AD/BEECH 65/64 Amdt 1

Wing Structural Fatigue Limitation 12/2010

Applicability: All models listed in the Retirement Schedule below. For models not listed, the

Authority must be contacted as a fatigue evaluation has not yet been carried out.

Requirement Retire from service the centre section and outer wing main spar lower caps, including

the centre section to outer wing attachment fittings.

RETIREMENT SCHEDULE

Model Retirement Life Average Take-off Weight Average Time per

Flight Stage

65 A65 27500 hours

3200 kg 45 minutes

65-80 22000 hours

3350 kg 45 minutes

65-A80 13500 hours

3500 kg 45 minutes

65-A80-8800 10400 hours

3700 kg 45 minutes

A65-8200 70 13500 hours 3500 kg

45 minutes

65-B80 10400 hours

3700 kg 45 minutes

Operation beyond the Retirement Life specified in the Retirement Schedule

In order to adopt a safety by inspection program to allow operation beyond the

retirement life specified in the retirement schedule, the following requirements must

be met: 1. For centre section and outer wing spar caps and attachment fittings that have

reached the retirement life, the registered operator must, before further flight,

present a damage tolerance evaluation to CASA that demonstrates to CASA’s

satisfaction that the Beech SIRM inspections (Chapter 57-11-00, Chart 201)

inspect these parts at all the probable locations of damage due to fatigue,

corrosion or accidental damage, per FAR 23.573(b). See note 1.

U.S. DEPARTMENT OF TRANSPORATION

FEDERAL AVIATION ADMINISTRATION

Airworthiness Directive

89-25-08 BEECH: Amendment 39-6410.

Applicability: Models 65 (Serial Numbers (S/N) L-1, L-2, L-6, LF-7 through LF-76, and

LC-1 through LC-180); 65-80 and 65-A80 (S/N LD-1 through LD-244); 65-A80 (S/N LD-245

through LD-269) when Beech Modification Kit No. 80-4004-1 or -3 is installed; and 65-B80

(all S/N) airplanes certificated in any category.

Compliance: Required as indicated after the effective date of this AD, unless already

accomplished.

To detect possible fatigue cracking of the wing main spar lower cap and associated

structure, accomplish the following:

(a)

Within the next 200 hours time-in-service (TIS) after the effective date of this AD,

or upon accumulating 3000 hours TIS on Models 65-80 and 65-A80 airplanes, or upon

accumulating 5000 hours TIS on Models 65 and 65-B80 airplanes, whichever occurs later,

unless previously accomplished per AD 70-25-01, Amendment 39-1609, and thereafter at

intervals not to exceed 1000 hours TIS (except as provided in paragraph (b) below) after the

initial inspection, inspect the wing lower forward spar attach fittings, center section and

outboard wing spar caps adjacent to the attach fittings by visual, fluorescent penetrant and eddy

current methods as specified in the applicable section of Beech Structural Inspection and Repair

Manual (SIRM), P/N 98-39006, Revision A4, dated May 1, 1987.

NOTE 1: Beech offers a two-day training course free of charge to qualified personnel

who have prior knowledge of eddy current inspection techniques. A listing of Beech Corporate

maintenance facilities may be obtained from the sources contained in paragraph (e) of this AD.

A listing of other facilities employing qualified inspectors is not available.

(b)

At each inspection required by paragraph (a) above, inspect any reinforcing strap

installed per Supplemental Type Certificate (STC) SA1583CE for proper tension and condition

in accordance with Aviadesign Engineering Order E.O. B-8001, Issue 3, dated May 30, 1985.

Correct any discrepancy prior to further flight. For airplanes equipped with STC SA1583CE

and inspected in accordance with paragraph (a) above, the repetitive inspection interval of 1000

hours TIS in paragraph (a) above may be extended to 3000 hours TIS.

(c)

If any crack is found in a main spar lower cap or fitting, prior to further flight

repair or replace the defective part using the instructions and limitations specified in the SIRM

or other FAA approved instructions provided by Beech Aircraft Corporation.

(d)

Airplanes may be flown in accordance with FAR 21.197 to a location where this

AD can be accomplished.

(e)

An alternate method of compliance or adjustment of the initial or repetitive

compliance times which provides an equivalent level of safety, may be approved by the

Manager, Wichita Aircraft Certification Office, FAA, 1801 Airport Road, Room 100, Wichita,

Kansas 67209; Telephone (316) 946-4400.

NOTE 2: The request should be forwarded through an FAA Maintenance Inspector, who

may add comments and send it to the Manager, Wichita Aircraft Certification Office.

All persons affected by this directive may obtain copies of the documents referred to

herein upon request to the Beech Aircraft Corporation, Commercial Service, Department 52,

P.O. Box 85, Wichita, Kansas 67201-0085; or Western Aircraft Maintenance, 4444 Aeronca

Street, Boise, Idaho 83705; or may examine these documents at the FAA, Central Region,

Office of the Assistant Chief Counsel, Room 1558, 601 East 12th Street, Kansas City, Missouri

64106.

There are rules that say you ‘must have regard to ... the manufacturer’s maintenance schedule’ (CAR 42M)—the Beech manual. There are four overriding CASA Airworthiness Directives (AD/BEECH 65/22 Amdt 4, AD/BEECH 65/34 Amdt 5, AD/BEECH 65/57 Amdt 4 and AD/BEECH 65/64 Amdt 1) which add to and subtract from the Beech manual.

And then you still have to check the FAA AD. CASR 39 says to do FAA ADs for American aircraft. Except you only have to do FAA ADs issued after 1 October 2009. So, you have to get the FAA AD and check its date. It is 4 January 1990, so it does not affect you. If the FAA were to revise the AD, then it would affect you, but you would wonder how because of conflict with CASA’s ADs.

If you wanted to change the maintenance, the Type Acceptance Certificate (A118 Issue 5) would tell you that CASA accepted the FAA’s airworthiness standard (mainly CAR 3) unconditionally. But then you would find that one of the ADs (AD/BEECH 65/64) has added a condition (FAR 23.573, which no other country requires). The result is confusion and more risk of error. Why does CASA not collaborate more with other major authorities, especially the FAA?

TrickeryFinally, trickery. Maintenance can play tricks on maintainers just as flying can play tricks on pilots. There are illusions. They are not just for magicians. An illusion is any ‘false or unreal perception or belief’.

We know a lot about illusions for pilots. There are warnings, like the Pilot Safety Brochures from the FAA:

Figure 6

Figure 5

Figure 7

Figure 8

A final approach over a downsloping terrain with a flat

runway may produce the visual illusion that the aircraft is

lower than it actually is. If you believe this illusion, you

may respond by pitching the aircraft’s nose up to gain

altitude. If this happens, you will land further down the

runway than you intended (Figure 6).

A final approach to an unusually narrow runway or an

unusually long runway may produce the visual illusion of

being too high. If you believe this illusion, you may pitch

the aircraft’s nose down to lose altitude. If this happens too

close to the ground, you may land short of the runway and

cause an accident (Figure 7).

A final approach to an unusually wide runway may

produce the visual illusion of being lower than you actually

are. If you believe this illusion, you may respond by

pitching the aircraft’s nose up to gain altitude, which may

result in a low-altitude stall or missed approach (Figure 8).

A final approach over an upsloping terrain with a flat runway

may produce the visual illusion that the aircraft is higher than

it actually is. If you believe this illusion, you may respond by

pitching the aircraft nose-down to decrease the altitude,

resulting in a lower approach. This may result in landing short

or flaring short of the runway and risking a low-altitude stall.

Pitching the aircraft nose-down will result in a low, dragged-in

approach. If power settings are not adjusted, you may find

yourself short of the runway, needing to add power to extend

your flare. If you do not compensate with power, you will land

short or stall short of the runway (Figure 5).

A Black-Hole Approach Illusion can happen during a final

approach at night (no stars or moonlight) over water or

unlighted terrain to a lighted runway beyond which the

horizon is not visible. In the example shown in Figure 9,

when peripheral visual cues are not available to help you

orient yourself relative to the earth, you may have the

illusion of being upright and may perceive the runway to

be tilted left and upsloping. However, with the horizon

visible (Figure 10) you can easily orient yourself correctly

using your central vision.

A particularly hazardous black-hole illusion involves

approaching a runway under conditions with no lights

before the runway and with city lights or rising terrain

beyond the runway. Those conditions may produce the

visual illusion of a high altitude final approach. If you

believe this illusion you may respond by lowering your

approach slope (Figure 11).

Figure 10

Figure 9

Figure 11

Peripheral VisionPeripheral vision, also known as ambient vision, is involved with the perception of movement (self and surrounding environment) and provides peripheral reference cues to maintain spatial orientation. This capability enables orientation independent from central vision, and that is why we can walk while reading. With peripheral vision, motion of the surrounding environment produces a perception of self-motion even if we are standing or sitting still.

Visual ReferencesVisual references that provide information about distance, speed, and depth of visualized objects include:

distances.

Nearby objects are perceived as moving faster than distant objects.

front of another is perceived as being closer to the observer.

Varying texture or contrast of known objects at different distances. Object detail and contrast are lost with distance.

light and shadows.

More distant objects are seen as bluish and blurry.

The flight attitude of an airplane is generally determined by the pilot’s visual reference to the natural horizon. When the natural horizon is obscured, attitude can sometimes be maintained by visual reference to the surface below. If neither horizon nor surface visual references exist, the airplane’s attitude can only be determined by artificial means such as an attitude indicator or other flight instruments. Surface references or the natural horizon may at times become obscured by smoke, fog, smog, haze, dust, ice particles, or other phenomena, although visibility may be above VFR minimums. This is especially true at airports located adjacent to large bodies of water or sparsely populated areas, where few, if any, surface references are available. Lack of horizon or surface reference is common on over-water flights, at night, or in low visibility conditions.

Visual Illusions Visual illusions are familiar to most of us. As children, we learned that railroad tracks—contrary to what our eyes showed us³don’t come to a point at the horizon. Even under conditions of good visibility, you can experience visual illusions including:

Aerial Perspective Illusions may make you change (increase or decrease) the slope of your final approach. They are caused by runways with different widths, upsloping or downsloping runways, and upsloping or downsloping final approach terrain.

Pilots learn to recognize a normal final approach by developing and recalling a mental image of the expected relationship between the length and the width of an average runway, such as that exemplified in Figure 2.

Figure 2

Figure 3

A final approach over a flat terrain with an upsloping runway may produce the visual illusion of a high-altitude final approach. If you believe this illusion, you may respond by pitching the aircraft nose down to decrease the altitude, which, if performed too close to the ground, may result in an accident (Figure 3).

A final approach over a flat terrain with a downsloping runway may produce the visual illusion of a low-altitude final approach. If you believe this illusion, you may respond by pitching the aircraft nose up to increase the altitude, which may result in a low altitude stall or missed approach (Figure 4).

Figure 4

Spatial Disorientation

Visual Illusions

OK-11-1550

SPATIAL DISORIENTATION:

Seeing Is Not Believing

Spatial Orientation

Our natural ability to maintain our body orientation and/

or posture in relation to the surrounding environment at

rest and during motion. Genetically speaking, humans are

designed to maintain spatial orientation on the ground.

The flight environment is hostile and unfamiliar to the

human body; it creates sensory conflicts and illusions that

make spatial orientation difficult, and, in some cases, even

impossible to achieve. Statistics show that between 5 to

10% of all general aviation accidents can be attributed to

spatial disorientation, and 90% of these accidents are fatal.

Spatial Orientation on the Ground

Good spatial orientation on the ground relies on the

effective perception, integration, and interpretation of

visual, vestibular (organs of equilibrium located in the inner

ear), and proprioceptive (receptors located in the skin,

muscles, tendons, and

joints) sensory

information. Changes in

linear acceleration,

angular acceleration, and

gravity are detected by

the vestibular system and

the proprioceptive

receptors, and then

compared in the brain

with visual information

(Figure 1).

Figure 1

Spatial Orientation In Flight

Spatial orientation in flight is sometimes difficult to achieve

because the various types of sensory stimuli (visual,

vestibular, and proprioceptive) vary in magnitude,

direction, and frequency. Any differences or discrepancies

between visual, vestibular, and proprioceptive sensory

inputs result in a “sensory mismatch” that can produce

illusions and lead to spatial disorientation.

Vision and Spatial Orientation

Visual references provide the most important sensory

information to maintain spatial orientation on the ground

and during flight, especially when the body and/or the

environment are in motion. Even birds, reputable flyers, are

unable to maintain spatial orientation and fly safely when

deprived of vision (due to clouds or fog). Only bats have

developed the ability to fly without vision by replacing their

vision with auditory echolocation. So, it should not be any

surprise to us that, when we fly under conditions of limited

visibility, we have problems maintaining spatial orientation.

Central Vision

Central vision, also known as foveal vision, is involved with

the identification of objects and the perception of colors.

During instrument flight rules (IFR) flights, central vision

allows pilots to acquire information from the flight

instruments that is processed by the brain to provide

orientational information. During visual flight rules (VFR)

flights, central vision allows pilots to acquire external

information (monocular and binocular) to make judgments

of distance, speed, and depth.


6

We know how runway widths and slopes can trick us into approaching too high or too low. We know how accelerations can trick us so we don’t know what’s up and what’s down. Illusions are serious. The FAA blames them for 10% of all general aviation crashes. 90% are fatal.

But what about illusions for maintainers? Are there any? Where are the warnings? At the FAA’s Symposium on Human Factors for Maintenance and Ramp Safety, in San Diego, in 2009, I warned about three illusions [18]. Here is a story about one:

1/11/11 3:51 PM

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In 1993 a propeller blade broke off a Nord 298 Mohawk airliner soon after take-off from Sydney. It was lucky the blade flew away from the fuselage and not into it. The blade broke because the airline, with CASA’s approval, had extended the time between inspections because they were not finding cracks. Extensions for this reason are common because the ‘nil findings’ argument sounds so plausible. But it is wrong. It is trickery. It is an illusion.

Unfortunately, there are no warnings about it in any of the maintenance publications. Some even encourage it.

The problem is lack of knowledge, one of Gordon Dupont’s ‘Dirty Dozen’. The knowledge lacking is the maintenance theory for inspection intervals. Maintainers lack it because it is in the design rules, not the maintenance rules. You have to know how the designer set the interval to know how to safely extend it. I talk more about this in another paper [19]. But, briefly, here is how it is done:

size

timeinterval

missable

critical

The curve shows how a crack grows with time. First, it is ‘missable’ (too small to find with the inspection method). Last, it is ‘critical’ (too big for the part to carry enough load). So, to find it safely in between, the time between inspections must be no longer than the ‘interval’.

What does ‘nil findings’ tell us about any of these variables? Do we know any more about crack growth? Do we know any more about what is missable? Or what is critical? No! We have no more information than the designer. ‘Nil findings’ is not evidence to extend an interval. I warn about this and other illusions for maintainers of old aircraft in my training courses.


7

ConclusionIn 1986, the FAA Administrator, the late Don Engen, said:

© Steve Swift Pty Ltd 2011

Don Engen

We spent over fifty years on the hardware, which is now pretty reliable. Now it’s time to work with people.

I’ll leave you with this quote from former FAA Administrator, the late Don Engen. In 1986 he said:

‘We spent over fifty years on the hardware, which is now pretty reliable.Now it’s time to work with people.’

For ageing aircraft, we’ve spent over fifty years on the engineering and the standards, which are now pretty reliable. Now it’s time to work with people - to convince them to apply the engineering and the standards already in our safety armoury more widely than we do now, to strive for clarity and simplicity as we do so, and to warn maintainers about trickery, about illusions. It’s all part of the human element in ageing aircraft safety, an area in which I hope to see future growth to meet the future challenge.

Thank you for your attention this afternoon.

Likewise, for ageing aircraft, we’ve spent over fifty years on the engineering, which is now pretty reliable. Now it’s time to work with people—to convince them to apply the engineering to all aircraft, not just the new; to strive for clarity and simplicity as we do; and to warn maintainers about trickery, about illusions. It is all part of the human element in ageing aircraft safety, an area in which I hope to see ‘future growth’ to meet the ‘future challenges’ (the Safeskies 2011 theme).

References[1] Final Report and Comments of the Netherlands Aviation Safety Board of the Investigation into the Accident with

the Collision of KLM Flight 4805, Boeing 747-206B, PH-BUF and Pan American Flight 1736, Boeing 747-121, N736PA at Tenerife Airport, Spain, March 27 (1977)

[2] Collision of KLM Boeing 747 PH-BUF and Pan Am Boeing 747 N737PA at Los Rodeos (Tenerife) on 27 March 1977, Recommendation 3.2, page 60, Ministry of Transport and Communication, Spain (1977)

[3] NTSB, Update on NTSB Investigations into Recent Beech 1900D Accidents and Incidents, NTSB Advisory, Washington DC, USA, November 21 (2003)

[4] ATSB, Investigation into Ansett Australia maintenance safety deficiencies and the control of continuing airworthiness of Class A aircraft, Canberra, Australia (2002)

[5] Swift, S., Sticks and Stones, in Proceedings of the 26th ICAF Symposium, Montreal, Canada, by Springer, Germany (2011)

[6] CASA, Take a Closer Look: Airworthiness and Ageing Aircraft, leaflet, Canberra (2011)

[7] Eastin, R., ‘WFD’–What Is It and What’s ‘LOV’ Got To Do With It?, First International Conference on Damage Tolerance of Aircraft Structures, TU Delft, The Netherlands (2007)

[8] Eastin, R., Swift, S., Rough Diamond, Proceedings of the 23rd ICAF Symposium, Hamburg, Germany, p. 43ff. (2005)

[9] Eastin, R., Contrasting FAA and USAF Damage Tolerance Requirements, ASIP, Memphis, Tennessee, USA (2005)

[10] ATA, MSG-3, Operator/Manufacturer Scheduled Maintenance Development, Air Transport Association of America, Washington DC, USA (2007)

[11] ICAO, Human Factors Training Manual, Doc 9683, 1 edn., Montreal, Canada (1998)

[12] Eagleson, R., Writing in Plain English, AGPS, Canberra, Australia (1990)

[13] Asprey, M., Plain Language for Lawyers, Federation Press, Leichhardt, Australia (2003)

[14] Clinton, W., Presidential Memorandum on Plain Language, USA (1998)

[15] FAA, Writing User-Friendly Documents, A Handbook for FAA Drafters, prepared for the FAA by the Plain English Network, USA (2000)

[16] ASD, ASD-STE-100, Simplified Technical English, Aerospace and Defence Industries Association of Europe, Brussels, Belgium (2010)


8

‘We spent over fifty years on the hardware, which is now pretty reliable. Now it’s time to work with people.’

[17] Gallagher, J., A Review of Philosophies, Processes, Methods and Approaches that Protect In-Service Aircraft from the Scourge of Fatigue Failures, Proceedings of the 24th ICAF Symposium, Naples, Italy, p. 1ff. (2007)

[18] Swift, S, Nil Findings, Three Nasty but Neglected Illusions of Structural Inspection Programs, Symposium on Human Factors for Maintenance and Ramp Safety, San Diego (2009)

[19] Swift. S., A Collective Approach to Aircraft Structural Maintenance Programs, presented at the International Air Safety Seminar, Honolulu, USA (2008)


9