Best Available Copy

Vo t kte ij;-ta l b o t*)t" lo g h

Techica Tnt)ýýiallon ,4ýric

If~~c~fio.11, , 2216 '7,iii 

;"I ~ AV2 ~ ,o lf nýLtai o

0c

Best Cop Aailabe 
Best

Available

Copy
Best Availjable, COPY

i- d'i-enina't c V the ~ a4i

:<Pm~~. Yho Untedtae.

.~c.;v *~~ r ~iihii y f~or its Q,-unlent or

B~~~ es -tla
*I , - - --

"Technical 4el)rt pocumontation Page

1. Report No. 2. Government Accession No. 3. Reciep~ni'iC~itatf-o.

4. Ti t a'ond Subtitle S:.' .JIprLt Date FEBRMW981 ,- -FECT OF DIFFERENT .RUNWAY SIZE ON .PILOT ,ERPORMANCE

DURING SIMULATED .NIGHT ANDING APProACHES . . Oa

8. Performing Organization Report No.

/'i Henry W.jMertens md Mark F./Lewis

- 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

FAA Civil Aeromedical Institute

P.O. Box 25082 1-1 Contract or Grant No.

Oklahoma City, Oklahoma 73125 Ad!EL_ E_ ko,,,o_,o_,o_. _ _" -_ 10. T pe of Report and Period Covered

,2 Spoasoring A nencv Name and Address

Office o: Avation Medicine e':t i / "

Fed"'al Aviation Administration

800 Independence: Avenue, S.W.. 1 14. Son.ori~n Agency Cde

.Washinl.tc n, D.C. 20591 ; ' 15IS.-$upplementary Not -It•

Wc k was perfifr:ed under Task AM-D-79-PSY-67 and AM-A-80/8l-PSY-85. IF Omit " "Both mnecdotal reports from pilots and theories of visual cues would predict lower

approaches to narrow or long runways than to wide or short runways. Practice with

particular width of runway would also be predicted to increase subsequent approach

angles flown to wider runways, and decrease approach angles to narrower runways. Two

experiments with instrument-rated pilots made quantitativo tests of these predictions

In Experiment I, three pilots flow simulated approaches and landings in a fixed-base

simulator with a computer-genorated-image visual display. Practice approaches were

flown with an 8,000-ft-long runway that was either 75, 150, or 300 ft wide: test

approaches were to runways with widths of 75,.100, 150, 200, and 300 ft. In

Experiment II, 40 pilots controlled the slant of a moving model runway during simulated niqht visual approaches. Five different models simulated runways from 100 to

300 ft wide and 3,000 to 9,000 ft long. As predicted, trainina on a wide runway in

Experiment I lowered approach angle in approaches to narrower runways: a narrow

practice runway also raised approach angles to wider runways. The magnitude of thesa

practice effects increased as distance from runway threshold decreased. There was

also 4 qeneral tendency for approach angles to decrease as runway width decreased.

The latter effect was corroboroted in Experiment It: in addition, generated approach angles decreased with increasing runway length. Giving half the pilots information

about runway size prior to each approach had no effect on responses. These findings add to the quantitative evidence of danger in night visual approaches due to visual

illusions and large variability in the visual perception of approach anqla.

V Approach and landing boctumnt is available to the public Visual cues throuqh the National Technical l"formation

Runway image site 8ervice, Springfield, Virginia 4•. tl

It. S. 56tv.. C05,4,I. 1., .O *. 'l St,,t C31.. ro ), . i. of. " -itp. 

Un-,las, if ied ........... il..., .

P... DOT P 1100.7tSj aept~d"i.. 1 C40011#04 id 0"0,4 .e.uet *11 
EFFECT OF DIFFERENT RUNWAY SIZE ON PILOT

PERFORMANCE DURING SIMULATED NIGHT LANDING APPROACHES

Introduction.

Visual illusions are considered to be an important factor in causing a

relatively high accident rate during night visual landing approaches (1-5,7-9,

12,13,15,23,24). Analyses of many civilian (11,12,13) and military (22)

accidents show that a relatively large number of aircraft crash short of the

runway in nighttime accidents unrelated to aircraft malfunction or adverse

weather. Many of these crashes are thought to have been caused by a lack of

visual information or to "erroneous information" in certain geographical

situations (e.g., sloping runway or sloping terrain around the runway) (12).

Until recently our knowledge of these visual illusions in the night approach

situation has been based, in a large part, on anecdotal accounts by pilots

who have survived some crashes. Because of the relatively high accident rate

in the night approach situation and the high cost of such accidents in terms

of human life, studies were undertaken to assess the alleged visual illusions

quantitatively and to determine their cause so that (i) pilots could be given

more explicit information concerning the hazards of night landing approaches

and (ii) a means of altering the approach environment might be identified so

as to effectively improve safety.

Previous research has shown that there is a general tendency for pilots

to fly lower approaches at night in "black hole" conditions, in which only

the edqo and end lights of an unfamiliar runway are available for vertical

guidance during the approach, and that the perception of approach angle is

extremely variable in this situation (10,17,20,21). This problem of low and

variable approaches at night may be the result of large variations in the

widths and lengths of runways at various airports. Some researchers have

suggested that if the width and/or lenqth of an unfamiliar runway differs

radically from that to which the pilot is accustomed, then the resulting

illusions cause systematic deviations above or below the desired glidepath

(1,7,23). Wulfeck, Weisz, and Raben (26) stated the problem and a theoretical

interpretation as follows:

A pilot approaching an unfamiliar airport may have trouble

..- judging position by the shape of the rectangle outlined by runway

lights, For example, after a few landings at one airport, he

learns the length-to-width ratio for the runway that will show him

he is approaching at the proper glide angle. If he goes into a

stringe airport where the runway is either shorter or wider and

attempts to use the sam perspective cues as.before, he will be

too high and come in at too steep an angle. Conversely, if the

runway is longer or narrower, he will come in too low. These

difficulties are to be expected from the geometry of the situa-

"tioe, and they .are confirmed by pilots' experiences, though no

experimental datA are available. (p. 262).

VII
This present study has been conducted in an attempt to quantify these

visual effects, or illusions. Experiment I was designed (i) to evaluate

deviations from the desired glidepath in simulated night approaches to unfamiliar runways of the same length but of various widths, and (ii) to determine the effect of practice with a particular runway width on subsequent

approaches to runways of different widths. Experiment II was then conducted

to compare the effects of varying runway width with the effect of varying runway length. The nighttime "black hole" was simulated in both experiments to

provide maximum effect of variations in runway length and width.

EXPERIMENT I

In the first experiment, an aircraft simulator with a computer-generated

visual display of the runway scene was used to measure performance during

approaches to runways of constant length but varying width, following practice

with a fixed runway width.

Familiarity with a particular runway width was accomplished by having

subjects fly 20 simulated visual approaches and landings to a runway that was

either 75, 150, or 300 ft wide. The effect of practice was then measured in

20 additional approaches in which five runway widths (75, 100, 150, 200, and

300 ft) were presented in random order. The theory of Wulfeck et al. would

predict that approaches flown to runways of differing width but constant length

would generate increasingly larger approach angles as a direct function of

greater runway width. Additionally, the function relating runway width to

approach angle should (i) shift upward following practice (familiarity) with

the most narrow (75 ft) runway and (ii) shift downward after practice with the

widest (300 ft) runway. The function should have an intermediate position

between the two previous cases when practice is given with a runway of intermediate (150 ft) width. That is, approach angles should shift upward for

widths greater than that of the practice runway and downward for test widths

narrower than practice.

Method.

subjects. Three men, pilots with instrument and multiengine ratings,

served as subjects. All had at least 20/20 acuity at the 30- and 40-inch.

distances measured by a test developed at 00 Civil Aeromadical Institute, and

'all passed the Farnaworth Lantern Test for color vision. The three subjects had experonce levels of 300, 4,200, and 7,000 hours of flying time.

"in . The subjects flew simulated Visual Flight Rules (VPR) approaches

.in a fixd-base simulator comprising a specially modified Analog Training

Computero. Model 610-1 simulator, with a computer-qentrated Image (WcI) visual

display mounted in the cockpit windshield to provide a oisulation of the outthe-windshiold visual scene synchronized with the simulated aircraft's flight.

The simulator was modified to produce electrical signals corresponding* to the

t ollowing paraoters of flight:. (i) X and Y coordinates, locating the aircraft on the ground plan* to the nearest. 3 ft. (ii) altitude coordinates to

the nearest foot, (iWi) roll, (iv) pitch, and tv) heading* The CXGI system has

been described elsewhere (18). A 17-inch multicolor cx•y tube was

2 T &Lc I ! I4•

""T4,,• y** ' 

ta
mounted in front of the pilot and ahead of the cockpit windshield, at a

distance of 3 ft from the pilot's eye. The display was controlled by a

Digital Equipment Corporation PDP-11/45 computer with a VB-11 display

processor and associated analog and digital inputs.

The display simulated a dynamic nighttime visual scene synchronized with

the maneuvers of the aircraft simulator. Data bases were constructed to

simulated runways 75, 100, 150, 200, and 300 ft wide. The length of all run-

"ways was 8,000 ft and only runway lighting was visible in the out-the-windshield

scene which simulated a "black hole" situation (lights simulating approach

lighting, taxiways, terminal areas, other runways, etc., were excluded). The

intensity of all simulated runway lights varied with distance and had a

realistic appearance.

Procedure. In the first experimental session, each subject's acuity and

color vision were tested. The subjects were then acquainted with the simulator. Recommended flap settings, airspeeds, and vertical speeds to be used

"were discussed at that time. Thirty to forty preliminary flights were then

made to let each subject become familiar with the simulator before the

experimental runs were begun. Each flight in both preliminary and experimental trials consisted of takeoff and climb to a designated altitude on a

constant heading. When the subject had established level flight at the

designated altitude and proper heading, the simulated position of the aircraft

was moved by computer command to a position approximately 5 1/2 to 6 1/2 miles

from threshold on the extended centerline of the runway. The designated

altitude assigned for each approach was randomly selected from a table ranging

from 1,100 to 2,700 ft in 100-ft steps. Although the subject always knew the

altitude from which the approach was started, he was not informed of the

distance from the runway at the beginning of the approach. The task of the

subject during both preliminary training and testing was to fly a "normal'

glidepath angle during the approach and to touch down about 1,000 ft upwind

from the runway threshold.

There were three conditions of the experiment in which each subject

participated. Each condition •onsisted of four experimental sessions with

one session per dO7. These four sessions wore divided into two familiarization (practice) sessions and two test sessions. Three runway widths (75, 150.

and 300 ft) comprised the three conditions used during the practice session*.

in each condition, the two practice sessions comprised 20 approaches (10 per

session) to the appropriate practice runway. The two practico sessions vore

"followed by two test sessions in which approaches were made to runways of five

widths: 75, 100, 150, 200, and 300 ft.

W:• The 10 tout approaches in each test session consisted of two blocks of

five approaches with all five widths given in a different random order in each

A block. therefore, following practice approaches in a particular condition,

each subject made a total of four test approachos to each of the five test

runway widths. It should be noted that in ptelimina', lrials, which were

given to acquaint subjects with the sioulator prior i*. "r• f tst sxporimentl

practice and test sessions, the width given each subject corresponded to the

runway width adMinisterad during the practice sessions of the first dxperimental condition. 3

p)I
The order in which the three experimental conditions (practice runway

widths) were given was different for each subject. The three orders were: Subject 1-75, 300, 150 ft; subject 2-150, 75, 300 ft; subject 3-300, 150, 75 ft.

Results.

In each test trial, simulated altitude and distance of the aircraft were

recorded at 1-second intervals during the approaches. These data were then

converted to generated approach angles (calculated by finding the angle whose

tangent was the ratio of generated altitude to distance from the desired touchdown point, 1,000 ft upwind from threshold).

Means of the approach angles (in degrees) as a function of practice runway width, test runway width, and distance, were evaluated by analysis of

variance. Distance was evaluated in this analysis by obtaining the mean

approach angle in each of the four l-nmi segments of each approach over the

range of distances from 4-nmi (24,000 ft) to thrushold. The significant effects

in this analysis were the main effects of practice runway width (p < .05) and

J 4.0- 4.0 b

4.

1 3.0 3.0 y

( a . 0 - 2.0,

-eO Subject I

WL o 1.0o U Subject 2 A"--- Subject 3

-4

. .0--0 Average

1, - 0 100 200 300 0 100 200 300

PRACTICE RUNWAY WIDTH TEST RUNWAY WIDTH

(Feet) (Feet)

Pigureo 1. TIthe mi~tn effoct# of (A) practice ond (0) tost trutnway width

an qetearted aIroa-ah ah'le in individual nubj ets.
DISTANCE INTERVAL

IJ 5,O 0- 6.000 ft. 5.0 6.000-12.000 ft. 5.0 12.000-18.000 ft. 5.0 18.000-24.000 ft.

-J

0

2

4< .0 4.0 4.0 40

oAA T

Ow0 3 3.0- 3.0- .

a..

o 2.0 2.0 2.0 2.0

J Practice Runway Width

to. * 75 ft. <• 10 1.OL 1.0 1.O- 'I U 950 ft.

Id 300 11.

w 0.0 1 0 .0L 11 1 1 J 1 0.0 .1 0.0 i 1 1_ ... 0 100 zo0 300 0 '00 200 300 0 100 200 300 0 100 200 300

TEST RUNWAY WIDTH (Feet)

Figure 2. The effect of practice and test runway width in each of the

four l-nmi segments of approaches from 24,000 ft to threshold.

4 the interactions of both practice runway width with distance (P_ < .01) and

test runway width with distance (p < .01). Figure IA shows the significant

main effect of practice runway width for each subject as well as for data

averaged over subjects. Mean approach angles generated by pilots decreased

as a function of practice runway width for all subjects. The effect of test

runway width is shown in Figure lB. Although the average over subjects

indicates an increase in mean approach angle with test runway width, the

"curves for the individual subjects show that this trend was consistent. for

only one subject.

The significant interactions of practice and test runway width with

distance are shown i Fin.gtre 2, where mean approach anqles are plotted as a

function of practice and test runway width separately for each of the four

*1-emi distance intervals between 24,000 ft and threshold. Pigure 2 shows

that the tronds In the main effects of both practice and tent runway width

are venerated at t•, neartdis•tance interval and decrease with distance

Sfrom runway threshniJ. Although the main effect of test runway widtith was not

*-consistent in -the thrieý subjects when dat"a wore avoraqed over all distantces, a

-§larqo effect of toet runway width i adpparont at tho nea•@st disatavc interval.

To ovaluate the evnistleyc of that result in the data for individual gubJ@oethe in•orctih of io ractieo And ttst runway width In the diotance Interval from ~Žft, to threshold was plotted In rigure 3. for each s ect. Te'ata

CthM a ait. @(f .ect of teot runway width# with approach atwle In.reasing at a

eqvction Of teot run•way width in the data of gbject- I and. 2. Although the

posibiit ofa imila trend iA tauggsted, in thevdata of subject I in the

Acurves for the 75-a and ISO-ft practice cotwitionsi, thist subject's data are

Sunite variable Andi thoecurve for theo 300-tt twacr~icc condition ckairly' does

not "upport thig trend. in the iatter curvo, approach ;xlseI@ net d have We 

A pronouncod V-shape, the. curve doteaeases consistently as teat runwav

--
jWe.0o SUBJECT I 6.0 SUBJECT 2 6.0- SUBJECT 3

0

< 4.0- 4.0- 4.0

03.0- 3.0- 3.0-

a:

Q.

4? 2.0- 2.0 2.0-

Li X Practice Runway Width

I-Se A0 75 ft, Cr1.0- ,.ee 1.0- * 15 t. 0

z A 300 I t.

00,01 o0 1 .c

0 too 200 S00 0 100 200 300 0 100 200 3oo

TEST RUNWAY WIDTH

(Feet)

Figure 3. The effect for each subject of practice and test runway width

in the last mile of approaches.

width increases up to 200 ft and then increases dramatically. Tito main effect

of practice runway width as shown in Figure 3 is consistent in all three subjects and in accotJ with theoretical predictions. Agreeme~nt with the theory

is loss clear in the case of the effect of test runway width due to'varlability in responses, but the predicted increase in approach angle with test.

runway width its supported by trends in the data at near distances.

Variability within the responses of an individual subject was measured

by calculating the range of responses in the four approaches made in a particular experimental condition. Mean intrauubject, ranges for each practice rxinway width# tent runway width, and distance are shown in Table I. these data

were not given. further statistical analysis. The only variabl, affecting

intrasubject response variation was distcnce. The intrasubject. range of

approach angles consistently increased an distance from runway threshold

decreased. There was no consistent effect attributable to practice runway

width or test runway width. 0itfeoroneas among subjects were also not groat.

The most Important finding was that the range of approach angles was quite

large in the last mile of-the approach in all three subjectsi intnrsubject

rarq. approached a value of 30 in the responses of two subjects.

Variation betwe~en subjects in approach angtlo was measured In tens of

* . the range of individual subject means for each combination of practice runway width, test rumway width, and distance-interval, thetea intersubject
TABLE 1. Intrasubject Variability (Range) of Generated Approach Angles

(in degrees) as a Function of Practice and Test Runway Widths and Distance

Subject

Practice Runway Si S2 S3 Mean

75 ft 2.26 1.64 1.77 1.89

150 1.49 2.31 1.33 1.71

300 1.13 1.36 1.33 1.27

Test Runway

75 ft 1.76 1.89 1.26 1.64

100 1.28 1.50 1.27 1.35

i.89 1.86 1.91 1.89

200 1.54 1.54 1.46 1.51

300 1.6? 2.07 1.49 1.74

Dlistance Interval1

0 -1 uizi 1.87 2.71 2.7S 2.44

1 -2 1.66 1.89 1.27 1.60

2-3 1.54 1.47 1.05 13

3 4 1.44 1.01 084 1.10

Variability da nta aresumrird inl table 2. -The averaw intarjiufrjec range -- is qivon for ,_ih pr~actice ruwavy widt~h, tatt runway width, aind distance

Interval. Again# only distance appa=Ll to be aystma~tira1.1y related to

Variability.

This axperifflant was an aittcI~t to quantity a visual illusion to the

pilot's peorception of vertical position- in t06 night aproach dituation duo

4 to variation in rtinway wiUth and prior practice with particular runway width&.

Anecdotal raiernteoi to runway width I1usiong in the aviation literaturo

augg~est that toorceptual crrors in judgmaots of 'approach any1e as a function
TABLE 2. Intersubject Variability (Range) of Generated Approach Angles

(in degrees) as a Function of Practice and Test Runway Width and Distance

Practice Runway

(ft) Range

75 1.22

150 1.44

300 1.13

Test Runway

(ft)

75 1.49

100 .86

150 1.37

200 1.10

300 1.49

tDistance Interval . (:ni)

0- I 1.94

1.16

2 * 3 1.01

3•-4 0.94

of difference: between familiar and otr-mnqe runwiys are many dnd consistont.

The present experiment eonfirmed the conaist@nt ffoect, in threa pilots, of

practice with a partiettl4ar r.nnwy on mibheuont qenoratd pproach dwals with

runways of difforinq Aire. The profent ftininq al-go indicates that visuakl

owieriencos with a particular runway over the short t@rm (only 20 practice

approacho~es acouufieiwtt to btas responoes. Thus, sfemiliarlty"~ with a

particular -runway Site .ýwpar3 to loge it-1 efect as a func tion of intervening

exparionce with a runway of diffroent Dnie.

Of partic-ular inportance-- to pilots, we believe, wat the findinq that in

"tho last gile of the -4pproah to i partitular ruway, the biasing effects oa

* visual experie-ca with a pArticular (prior) runway of a different width will

-. result in the later approach beinq. lown above or bolow the deired approach

path by as mtuch as Onte toIestoe or pore, on thL daeraqa. the fact that the

variability of approach anqiloe va itanow, both within the approaches of an

individual pilot and anootj all pilot subýjeCts, doos not det-ract from. the

importance ýof the prosent findinqs. Rather. it servos4 to eWphnise the fact

V' •that the pilot'.g por•eption of vortical position ie iiprocize during visual

approach@s at night. The pilot'sg porceoptio Af approach iintole in repeated

apptoachas in the same environwet is,. therefore, best decribed by a distribution of responges in which variability, as •eil as eontral tendaneny, ustbe

* considerod. lhe eoffect of the. runway width illusion is to shift the whole

4 •••m e i ni im••~ !m n|rn=
distribution of responses that can occur in a given runway situation up or

down the scale of approach angles. in this regard, a low approach and resulting crash short of the runway is most probable in the case when a response in

the lower extreme of the distribution occurs and when the pilot's recent prior

experience with a wider runway has shifted his response distribution downward.

Likewise, a high approach with a probable overshoot of the runwa3⁄4 is most

likely to occur after recent experience with another more narrow runway.

i ~EXPERIMENT 11I

Altrhouqh Experiment I did not vary the length of the simulated runway,

the theory of Wulfeck et al. (26) also predicts that approaches flown to

runways of differing length but constant width should generate approach angles

that decrease as a direct function of test runway length. This prediction was

tested in Experiment I1, and the effect of variation in runway width reexamined, again in a simulated nighttime "black hole" situation. The comparison of length and width effects has significance not only in quantifying

visual illusions in the night approach to landing situation but also has

significoattce in determining which cues in the runway image are important in

the perception of the approach path at night.

A different task. requirinq less training of subjects, and a different

visuol simulation techniquewere used in Experiment 1I to study runway size effu:ts. Diffor•et lenqths (3,000 to 9,000 ft) and widths (100 to 300 ft) of

rkunway lighting systems were simulated with scale models. The0 cask of the

pilot wan always to ioontrol a model, as it moved toward him over the simulated

distance range of 23,000 to 5,000 ft from threshold, to produce a "normal"

approdch OMul, And to produce thie siwe "normat" Ipproach anmle on all attempts.

The offect of. prior knowledqo of runway si-o was also studied by giving half

the, pilots Information about runway size prior to each simulated approach..

Fujcs ortymole pilots served, as subject-s. They were between 25 and

(Vt vcoAyx of aqe and were active. in: ir earriet, military, or 4eneral aviation.

All hadjW 40v0auity at the far point, and all possessed, instrumeant rati Ys. i 

Thep nubthjetg woro randomly attoiunet to two groups differing in whether they

were given uvi i qinr teWA rmto n twenty subjects in one group wore hot .. givesi runway sig iftforatiOn: they had a median nvorienee levol of. 1 ,950

tot~al flyifnq h-urs with a demi-intorqtartile ranqe of 1,850 hours. The 20

§iuhJkE#t in. rh~iqroup that V~as given runway site informaion had a median

exptrienc* k-vol of 1l75 0 Mitts with an interquartile ranoe of 2#61l5 hours.

2.Ninet pilot# in the "Nto Site Infornationo 4roup Andi seven pi lots In the Sizeix

= Infornation 6rtnup had heavy ulwtiri4inie Airfrat, Otptieoa•o. All othor *shWegts flow light sitwle 4nd twin. onqine aircrAft.

Apraus te "W rau used In this SU4V has bkden described in dotal

pevitutly' (18). Th .niqhttie alpproach scoen was tiwulated with O•i@ %Woels

of* rnwaay .liqhting synt*~a cootainingq edqe and end lights only, with lights

colorod apptopriately. Runway width wa# varied in three of the m cls. The

widths terv 100t.150, .imlatod and 300 it# and all three had a. s lad

.9

,4
LB'

B2

M2

H

P2

MIM. P

'2A2

Figure 4. Schematic of apparatus (Al and A2, removable targets for aligning

optical system; B1 and B2, baffles; C, cart; F, rotation axis; H,

horizontal line-of-sight; Ml and M2, mirrors; 0, eye position; P1,

P2, P3, segments of the optical axis; Q, apparent axis of radial

motion; R, runway model; T, track; B, viewing angle; 0, model slant.

length of 6,000 ft. The two additional models had 150-ft widths, but had

lengths of 3,000 and 9,000 ft. Length/width ratios of 20:1, 40:1, and 60:1

were represented in these models. The models were created in 1,200:1 scale

using a fiber optic technique described previously (18). The light box on

which the models were mounted for experimental trials contained fluorescent

sources and intensity was adjusted to simulate an average luminous intensity

of 120 candelas for individual white runway lights.

A schematic diagram of the apparatus is shown in Figure 4. It consisted - of a runway model (R), the cart and track (C and T) on which the model runway

moved toward the subject, and a mirror viewing system (Ml and M2). The model

was viewed monocularly from an enclosed observation booth through a 12-mm

aperture at Bl. This arrangement enabled the model to move directly toward

the observation point along a virtual optical path (Q) which was 30 below the

straight ahead direction (H). Since the model was seen in an otherwise dark

field, variation in the slant of the model (0) appeared to the subject as a

change in approach angle. The slant of the model and, hence, apparent

-approach angle, was controlled by the subject during the experimental trials.

"Model slant was measured and recorded to the nearest 0.1° throughout each

.experimental trial. Targets Al and A2, shown in Figure 4, were only present

S - during optical alignment of the system.

10
Procedure. The subject's task was to control the runway model as it

moved toward him in order to produce what looked like a "normal" approach

angle, and to produce the same angle on every subsequent trial. During each

trial, the model was visible and was controlled continuously by the subject

as it moved toward the observation position over a simulated distance range

of 23,000 ft to 5,000 ft from threshold. The sim'ulated approach speed was a

constant 125 knots.

After familiarization, four practice trials were given each subject with

the 150-ft-wide, 6,000-ft-long runway. Fifteen test t:ials with all five

runways followed. Prior to the start of each test trial, the model was set

at a simulated approach angle of 0.50, 3.00, or 5.50. Each of the 15 combinations of five runways and three starting angles appeared once in random

order in the series of test trials given each subject. In the "Size Information Group," subjects were told the simulated size of the runway prior to

each trial. No feedback concerning performance was given any subjects during

the experimental period. Experimental sessions lasted approximately 2 hours

for each subject.

Results.

Approach angle was the dependent variable. It was defined as the angle

between the line-of-sight to the runway threshold and the plane of the runway

model. Approach angles were measured for the present analysis at half-mile

(3,000 ft) intervals from 17,000 to 5,000 ft from threshold.

W 3.00

2.0 ISO ,000 4

4

0 RUNWAY SIZE

0 300, X 6.000'

* 1100 s X 3.000,

11 ISO, X 6,000' -A, 150' X 9,000'

100o X0 6.000'

.000 6.,000 11.000 14,000 17.000

DISTANCE FROM THRESHOLD (FEET)

Figure 5. The offect on genorated approach angles of runway sizo and

distance fr~om runway throshold. w4t

TI:
-J 4.0

3.0-

0 o0 r2.0-

I- 1.0- * WITH SIZE INFORMATION

0: 0 WITHOUT SIZE INFORMATION

Zu 0.0 - I I

(D 150'x 300'x 150'x I0O'x 150'x

3,000 6,000 6,000 6,000 9,000

RUNWAY SIZE

Figure 6. The offect on generated approach angles of verbal size

information and actual runway size.

The effects of varying iunway size and distance on qenerated approach

angles are illustrated in Figure 5. soth runway size and distance had effects

statistically significant at the 0.01 level, an did their interaction. For

the three 6,000-ft runways, qenerated approach angles increased as runway width increased. Mean approach angles for the 300-, 150-, and 100-ft-wide

runways were 2.800, 2.23P. and 2.010, respectively. For the three 150-ft-wide

runways, approach angles increased as runway Aenth decreased. Mean approach

angles for the 3,000-, 6,000-, and 9,000-ft runways were 2.74°, 2.230 and

"1.96", respectively. Runways of different sizeos but with identical length/

* width ratios, produced similar approach angles on the average, and mean

approach angle increased as a function of runway length/width ratio. However,

when length anr.d width effects for individual subjects were examined, there

I ~was no significant correlation found (r a 0.05).

The effect of knowledge of runway size is shown in Figure 6. Mean

approach angles were approximately 0.50 higher in the group given knowledge of

runway size prior to each trial, but that effect was not statistically

significant. There wav also no interaction of knowledge of runway size with

variation in simulated runway size in the production of approach angles.

12

ft
The muin effect if starting angle was significant at the .01 level as

was its interaction -.'ith distance. In general, approach angles increased as

a function of starting angle. The difference in mean approach angle between

the 5.5 0 and 0.50 starting angle conditions was 0.780 at the 17,00Q-ft distance.

This difference decreased to 0.250 at the 5,000-ft distance. There was no

interaction of start '.ng angle with either simulated runway size or information

a-out runvawy size.

TABLE 3. Intersubject Range in Degrees as a Function of

Runway Size and Distance From Threshold

RUNWAY SIZE (FEET)

DISTANCE 15O x 300 x 150 x 100 x 150 x (FEET) 3,000 6_2000 6,000 '6_000 _ 9,000 MEAN

J,000 4.68 6.55 5.88 4.49 4.56 5.23

8,000 3.90 5.26 4.59 3.79 3.95 4.30

11,000 4.59 4.55 3.85 3.06 3.48 3.91

14,000 4.98 4.14 3.44 3.56 3.43 3.91

17,000 4.51 3.33 3.54 3.33 3.86 3.71

MEAN 4.53 4.77 4.26 3.65 3.86

TABLE 4. Intrasubject Range in Degrees as a Function of

Runwov ',;iz and Distance From Threshold

RUNWat SIZE (FEF.r)

DISTANCE I5O x 00 x 10 100 x 150 x

I3L000 MM Q0_61Q220 ~ 60_00 9,1000 MEAN

5,000 ,90 1.07 .85 .73 .74 .86

8,000 .77 .77 .68 .73 .61 .71

11.000 .79 .87 .73 .72 .56 .73

14,000 .84 .98 ,;9 .7! .72 .82

17,000 .97 ;.02 1.05 .99 .83 .97

FMEAN .85 .94 .82 .78 .69

An iMportant finding contoras the variabil 4 t of responses betveen subJoets in a qivon oxperimontal condition. inte averago rang* of responses b-tweensubjects(intorsubject varahbility) o:,ei all experlmental confltions

i was 4.2'0. I.ntersubject range is shown in Tablft 3 as a function of runway sits

* and distanco. Thore Is a totenlecy for the intersubject rAnge of responsts to

vary invorsoel with both distanc. 4nd runway lenrthM/wdth ratio.
The range of responses within a given experimental condition was determined for each subject as a measure of intrasubject variability. Intrasubject

variability averaged over subjects is shown as a function of runway size and

distance in Table 4. In the case of the mean intrasubject range of responses,

variability again varies inversely with runway length/width ratio. Intrasubject variability initially decreases with distance, from 17,000 to 11,000

ft, and then increases at the nearest, 5,000 ft, distance. These fluctuations

in mean intrasubject range of responses were small, however, on the order of

0.20.

Discussion.

The present experiment did not permit feedback to the pilots concerning

their accuracy of response. Responses were analogous, therefore, to responses

to unfamiliar runways of widely varying size. The present study demonstrates

the existence of illusions due to variations in both runway lenqth and width

in simulated nighttime "black hole" situations. As runway length/width ratio

was increased from 20:1 to 60:1, approach angles decreased by 0.840, from

2.77 to 1.960, on the average. These findings, and the findings of Experiment

I, corroborate warnings of runway size illusions from anecdotal reports of

pilots, and have implications regarding which cues in the runway image produce

the illusions.

There are at least three cues involving runway image size and shape which

permit prediction of effects of varying runway width and length on pilot

judgment of approach angle. These are (i) linear perspective, (ii) runway

image height, and (iii) length/width ratio in the runway image. Linear perspective can be defined as the magnitude of the base anglos of the trapez ial

runway image when the pilot's eye is aligned with the extended centerline.

Linear perspective increases with approach angle and distance, and varies inversely with runway width. The linear perspective cue may predict an effect

of width if the pilot's perceptual system utilizes the natural relation between linear persýective and distance learned for a particular (familiar)

runway and the normal approach angle. Applying such a learned function to a

wider runway would cause the pilot to produce a higher than normal approach

angle, and a narrower runway would cause low approaches. This cue system

would predict runway width effects, but would not predict the effects of

varying runway length observed in the present experiment.

The second cue, runway image height, increases with approach angle and

runway length, and decreases with distance from the runway. Applyinq a

learned relation of image height to dintance would cause high approaches with

shorter than normal runways and low approaches with longer than normal runways.

The image height cue will predict runway length effects, but will not predict

the effect of vatying runway width that was observed in this study.

A third cue which will predict runway size effects on perception of

approach angle is the ratio of length to width in the runway image t26)

j describod above. It can be ahown gemetrically, for all runways with the

same ratio of actual lenqth to actual width, that the ratio of runway image

height to imago width of the far and is a function of only one variable,

14

ik1
approach angle (21). The ratio appropriate for a given approach angle

increases with actual length/width ratio in the runway, but is independent

of absolute dimensions of the runway. Applying a particular learned value of

image length/width ratio to runways with actual length/width ratios greater

or less than normal will result in a deviation below or above the normal

approach angle, respectively. The present finding of both length and width

effects is in agreement with predictions of the image length/width cue. The

lack of significant correlation between length and width effects, however,

suggests the possibility that image height and linear perspective, working

independently, may have caused the runway size effects observed. An alternative possibility is that the image length/width cue determined the illusions,

but response variability obscured the relation of length and width effects.

Additional research is required to discriminate between these possibilities.

The fact that variability of generated approach angles was large does not

detract from the importance of runway size effects. The effect of varying I. runway size is to shift the distribution of pilot responses that can occur in

a given situation up or down the scale of approach angles.

Giving pilots knowledge of runway size did not have any effect on the

magnitude of illusions due to variation in runway size. This finding most

probably reflects the unconscious nature of the process involved in the perception of approach angle. Harris (6) has theorized that due to the unconscious nature of perception, simply telling pilots of the danger of visual

illusions in night approaches will not lessen that danger as long as the pilot

still relies on the same vulnerable perceptual process. The present finding

supports Harris' view. The need for improved techniques of training pilots to

counteract visual illusions in night visual approaches and to adapt to different

runway situations is clear.

OVERVIEW

The findings of this study provide empirical evidence of illusions in

judgments of approach angle due to variations in both length and width of runways. The findings also demonstrate the interaction of recent practice with

a specific runway with those runway size effects. These findings add to the

accumulating body of experimental evidence concerning the existence of different sources of errors in the perception of approach angle, errors which make

the night approach situation dangerous, especially in the visual environment

called the 'black hole," where the only lights visible on the ground are the

edge and end lights of the runway (17,20,21). Those findings also support a

prediction of (i) increased chance of making a dangerous, low approach when a

pilot flieo 1 nighttime approach to an unfdmiliar runway that has a large ratio

,A of length to width and (ii) an evon greater danger if the pilot's recent

experience was with a runway with a smaller ratio of length to width.

Those data also support previous studies which show judgment of approach

angle to be extremely variable in the nighttime approach situation (10,17).

Although it is sometimes stated that cues in the runway image formed by the

boundarv-markin (edge) lights represont the minimum cues that a pilot needs

for landing (161, the reaults of the present study add to a growing base of

| | |
evidence that these cues may often be a source of rather large error in judgment of approach angle, and are, therefore, insufficient for a safe approach

to landing. The present findings also support the recommendation that landing

aids such as Instrument Landing Systems (ILS), and Visual Approach Slope

Indicator (VASI) systems be utilized at night to supplement natural visual

information at all airports where, otherwise, the lack of surrounding ground

lights forces reliance on ineffective visual cues even in good visibility

conditions. Although the problem of varying the amount of information on the

approach scene can be performed most easily in the laboratory or through use

of a computer-controlled aircraft simulator with a CGI visual display, there

remains a continuing need for studies of flight paths in actual night approaches

as a function of environmental conditions, including variation in runway size,

to validate the simulation data recorded in this study.

'4

16

fr
REFERENCES

1. Busby, D. E.: Visual Illusions: Runway Width and Slope. FAA AVIATION

NEWS, 14:12-13, 1975.

2. Busby, D. E.: Visual Illusions II: Terrain Features. FAA AVIATION

NEWS, 14:16-17, 1976a.

3. Busby, D. E.: Visual Illusions III: Atmospheric Distortion. FAA

AVIATION NEWS, 14:12-13, 1976b.

4. Busby, D. E.: Visual Illusions IV: Relative Motion. FAA AVIATION NEWS

14:7, 1976c.

5. Cocquyt, P.: Sensory Illusions. SHELL AVIATION NEWS, 178:19-24, 1953.

6. Harris, J. L., Sr.: What Makes a Visual Approach 'Nonvisual?' AIR LINE

PILOT, 46:14-19-, 1977.

7. Hartman, B. 0., and G. K. Cantrell: Psychological Factors in "Landing

Short" Accidents. FLIGHT SAFETY, 2:26-32, 1968.

8. Hasbrook, A. H.: Anatomy of a Landing Cue by Cue. BUSINESS AND

COMMERCIAL AVIATION, 29:54-60, 1971.

9. Hasbrook, A. H.: The Approach and Landing: Cues and Clues to a Safe

Touchdown. BUSINESS AND COMMERCIAL AVIATION, 32:39-43, 1975.

10. Hasbrook, A. H., P. 0. Rasmussen, D. M. Willis, and M. M. Connerst

Pilot Performance and Stress Response During Day and Night Visual Landing

Approaches, Unpublished paper presented at tha 1975 annual scientific

meeting of the Aerospace Medical Association, San Franciuco, California,

April 29 - May 1, 1975.

11. Kirchner, 0. R.: Critical Factors in Approach and Landing Accidents,

Part 1 - Statistics. Flight Safety Foundation, December 1960.

12. Kraft, C. L.t Measurement of Heiqht and Distance Information Provided

Pilots by the Extra-Cockpit Visual Scene. In: Visual Factors in

Transportation Systems: Proceedings of Spring Meeting, Coatnittee on

Vision, National Acadomy of Sciences, National Research Council,

S, Washington, D.C., pp. 84-101, 1969.

6, 13. Kraft, C. L.a A Psychophysical Contribution to Air Safetyt Simulator

4 Studies of Visual Illusions in Night Approaches. Int 11. L. Pick, Jr.,

H. W. Liebowitz, 3. E. Singer* A. Steinschneider, and H. W. Stevenson

(Eds.), Ps•choloqyt Prom Research to Practice. Now Yorks Plenum Press,

pp. 363-385, 1978.

14. Kraft, C. L., and L. W. Shaffer: Visual Criteria for Out of the Cockpit

* "+ Visual Scenes. In: North Atlantic Treaty Organization AGARD Proceedings

24903-1 to 3-8, 1979.

17

SI I I I II I
15. Kuhlman, R. L.: Approach With Care. FLYING, 78:88-90, 1966.

16. Langewiesche, W.: Stick and Rudder. New York: McGraw-Hill, 1944.

17. Lewis, M. F., and H. W. Mertens: Pilot Performance During Simulated

Approaches and Landings Made With Various Computer-Generated Visual

Glidepath Indicators. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE, 50:

991-1002, 1979.

18. Lewis, M. F., H. W. Mertens, and T. Kempsell: A Real-Time Graphics

Systems for RSX-IID. In: Proceedings of the Digital Equipment Computer

Users Society, 2:441-442, 1975.

19. Mertens, H. W.: Laboratory Apparatus for Studying Visual Space Perception of the Pilot in Simulated Night Approaches to Landing. PERCEPTUAL

AND MOTOR SKILLS, 45:1331-1336, 1977.

20. Mertens, H. W.: Comparison of the Visual Perception of a Runway Model

in Pilots and Nonpilots During Simulated Night Landing Approaches.

AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE, 49:1043-1055, 1978.

21. Mertens, H. W.: Runway Image Shape as a Cue for Judgment of Approach

Angle. FAA Office of Aviation Medicine Report No. AM-79-25, 1979.

22. Miholick, J. I.: Pilot Induced Landing Mishaps Where Visual Cues Were

a Factor. USAF Safety Officer's Study Kit, December 1977.

23. Pitts, D. G.: Visual Illusions and Aircraft Accidents. USAF School of

Aerospace Medicine Division (AFSC), Brooks AFB, Texas, SAM-TR-67-28,

1967.

24. Riordan, R. 11.: Monocular Visual Cues and Space Perception During the

Approach to Landing. AEROSPACE MEDICINE, 45:466-771, 1974.

25. Vinacke, W. E.t Illusions Experionced by Aircraft Pilots While Flying.

JOURNAL OF AVIATION MEDICINE, 18:308-325, 1947.

"26. Wulfeck, J. W., A. Weisz, and M. W. Raben: Vision in Military Aviation.

, Wright-Patterson Air Development Center, Air Research and Development

Command, Wright-Patterson AFB, Ohio, WADC Technical Report 58-399, 1958.

Qle

S.A

18
Destroy this report when it is no longer needed.

Do not return it to the originator.

Additional copies of this report may be obtained

from the National Technical Information Service,

U. S. Department of Commerce, Springfield, Virginia 22161.

The findings in this report are not to be construed as

an official Department of the Army position, unless

so designated by other authorized documents.

1'4 us* of erad4 'ire or tip hsvor 'lddfto Oaneitut* 3⁄4jowrverc of ,my COMMo..1i Prodiaot.