FAA-AM-82- 6

4 EFFECTS OF APPROACH LIGHTING AND VARIATION IN VISIBLE RUNWAY

LENGTH ON PERCEPTION OF APPROACH ANGLE IN SIMULATED NIGHT LANDINGS

Henry W. Mertens and Mark F. Lewis

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

FEBRUARY 9lSZ

Document is available to the public through the

National Technical Information Service

Springfield, Virginia 22161

Prepared for

U.S. DEPARTMENT OF TRPNSPORTATION

Federal Aviation Administration

Office of Aviation Medicine -T IC ,

W. 1ashington, D.C. 20591 'ELEC

oMAY24 1982 >

82 05 -24 178
NOTICE

This document is disseminated under the sponsorsWip of the

Department of Transportation in the interest cf information

exchange. The United States Government assumes no iiability

for its content or use thereof.
Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

FAA-AM-82-6

4. Title and Subtitle 5. Report DOat

EFFECTS OF APPROACH LIGHTING AND VARIATION IN VISIBLE FEBRUARY 1982

RUNWAY LENGTH ON PERCEPTION OF APPROACH ANGLE IN 6. Performing Organization Code

SIMIULATED NIGHT LANDINGS,_____________ SIMULATED NIGHT LANDINGS, h7 Performing Organization Report No.

7. Authorls)

Henry W. Mertens and Mark F. Lewis

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

FAA Civil Aeromedical Institute

P.O. Box 25082 11. Contract or Grant No.

Oklahaoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address

Office of Aviation Medicine

Federal Aviation Administration

800 Independence Avenue, S.W. 14. Sponsoring Agency Code

Washington, D.C. 20591

15. Supplementary Notes

Work was performed under tasks AM-D-79-PSY-67 and AM-A-80/81-PSY-85.

16. Abstract

Previous experiments in this laborator? have demostrated illusions due to variations

in both length and width of runways in nighttime 1 black hole' approaches. Even though

approach lighting is not designed to provide vertical guidance, it is possible that

cues from approach lights could interact with cues from runway lighting to reduce

illusions due to variation in runway size. Two experiments were conducted to evaluatE

the effect of approach lighting on perception of approach angle in simulated night

approaches. In the first experiment, 40 pilots made simulated visual approaches to a

150- by 6,000-ft runway with and without a 3,000-ft approach light system (ALSF-2).

Pilots controlled a moving runway model to produce a constant I'normal' angle of

approach over the distance range of 23,000 ft to 8,000 ft from threshold. In the

second experiment, 24 pilots made simulated approaches to a 150- by 6,000-ft runway

which was either fully visible or which had lights of the upwind half occluded. In

addition, a 3,400-ft abbreviated approach light system (SSALS) was used at three

intensities. Decreasing the visible length of the runway b occulting lights of the

far half increased mean generate' approach angles from 2.2 to 2 .7b in agreement with

results of a previous experiment involving similar lengths of runways. Neither the

presence of equal intensity approach lights nor uncomfortable glare from approach

lights 20 times brighter than runway lights had an effect of practical significance

on responses. These findings reinforce previous experimental demonstrations of the

importance of runway size cues related to varying runway length, and also show that

potential size cues provided by approach lights do not prevent illusions due to

variations in runway size__ _

17. Key Words 18. Distribution Statement

Approach and Landing Document is available to the public

Visual Cues through the National Tecinical InforAppioach Lighting mation Service, Springfield, Virginia

Runway Image Size 22161.

19. Security Clossif. (of this report) 20. 'ocurity Classif. (of this page) 21. No. of Pages 22. Price

Unclassified T classified 19

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

Q
EFFECTS OF APPROACH LIGHTING AND VARIATION IN VISIBLE RUNWAY

LENGTH ON PERCEPTION OF APPROACH ANGLE IN SIMULATED NIGHT LANDINGS

Introduction.

One of the most dangerous night visual approach situations is that in

which only runway lights are visible on the ground, a situation often called

the "black hole" by pilots. Recent experiments provide empirical evidence

of illusions in the "black hole" situation including a general tendency to

over-estimate approach angles to an unfamiliar runway (2,4,5) and a tendency

for approach angles to vary directly with runway width and inversely with

runway length (6). Those findings indicate the importance of runaway image

size and shape cues in tbe perception of approach angle in the "black hole."

Those experiments did net, however, consider the potential importance of

cues from approach ligiti- on perception in the "black hole." Even though

approach light systems .iot designed primarily to provide information for

perception of appioach le magnitude, some assessments have suggested that

they do (1,7,S). The pr,, ent experiments tested that possibility.

Theoretically, it is possible for approach lighting to affect

perception of approach angle magnitude in at least two ways. First, the

additional information from approach lighting might be expected to reduce

the above mentioned illusions that occur in the "black hole" and reduce

response variability. Second, glare from overly bright approach lights

might degrade visual information from runway lighting, causing systematic

errors or increasing the variability of approach angles. Both possible

interactions of approach and runway lighting were examined. Simulated night

approaches in the "black hole" were studied with two different approach

light systems in two experiments.

EXPERIMENT I

Experiment I compared approach angles in simulated nighttime "black

hole" approaches to two runways. One runway had only edge and end lights;

the second runway had, in addition, a simulation of the largest approach

light system currently used in the United States, as well as touchdown zone
and centerline lighting which are typically used with that approach light

system. The presence of approach lighting was evaluated with regard to

effects on illusions involving overestimation of approach angles and with

regard to effects on the variability of approach angle responses.

f'ethod.

Subjects. Forty men, pilots with instrument ratings, served as

subjects. They were between the ages of 25 and 60 years of age and were

active in air carrier, military, or general aviation. All had 20/20 visual

acuity at the far point, with correction if necessary. Their flying

experience ranged from 200 to 22,000 total hours with a median of 1,750

hours and a semi-int, quartile range of 1,950 hours. Sixteen pilots had

heavy multiengine experience; all others flew light single and twin engine

aircraft.

Apparatus. The nighttime approach scene was simulated with two models

of runway and approach lighting systems. One modeled edge and end lights

only, with lights colored appropriately. The other model also included

approach lights simulating a 3,000-ft Category 2 approach light system

(ALSF-2), without sequence.d strobe lights (7). In both models, the runways

had a simulated length of 6,COO ft and a simulated width of 150 ft. The

models were created In 1,20G:I scale using a fiber optic technique described

previously (3). The light box on which the models were mounted for

experimental trials contained fluorescent sources, and the intensity of

simulated white runway and approach lights was adjusted to simulate an

average of 120 candelas. A schematic diagram of the apparatus is shown in

Figure I. It consisted of a runway model (R), the cart and track (C and T)

on which the model runway movcd toward the subject, and a mirror viewing system (M and M2). The model was viewed monocularly from an enclosed

observation booth through a 12-mm aperature at BI. A head and chair rest

were used to position and steady the subjects head during experimental

observations. This arrangement enabled the mode] to move directly toward

the observation point along a virtual optical path (Q) which was 3*below the

straight ahead direction (H). The slant of the model (fa-), and hence,

apparent approach angle, was controlled by the subject during the

experimental trials. Model slant was measured and recorded to the nearest

0.? throughout each experimental trial. Only the simulated runway lighting,

and approach lighting when appropriate, were visible to the subject in the

otherwise dark "black hole" scene. Targets Al and A2, shown in Figure 1,

were only present during optical alignment of the system.
BI

82

M2

P1

P2 R.

MI P3

F 

A2

Al

C

T

FIGURE 1. Schematic of apparatus (Al and A2) removable targets for aligning

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

horizontal line-of-sight; 1 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; 0, viewing angle; 0, model slant.

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 samc angle on every subsequent trial. AL Lhe

start of each trial, the dim overhead light in the booth went out, the model

began moving toward the subject, and 5 s later the lights of the model were

turned on as the model reached the simulated distance of 26,000 ft from

threshold. The model was then controlled continuously by the abject as it

moved toward the observation position over a simulated distance range of

26,000 ft to 8,000 ft from runway threshold. The simulated approach speed

was a constant 125 knots.

After familiarization, involving two practice trials, four test trials

were given. The order of presentation of the two runway models in these six

trials was either ABAABB or BABBAA. Prior to the start of each trial the

model.was set at a simulated approach angle of 0.5aor 3.C*. The two

starting angles were alternated, and the order of starting angles was

reversed for half the subjects. No feedback concerning performance was

given to any subject during the experimental period. The experimental

session too! approximately one-half hour for each subject.

3 session too-
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 20,000 ft to 8,000 ft from threshold.

The effects of approach lights and distance on generated approach

angles are illustrated in Figure 2. Analysis of variance revealed

statistically significant effects of approach lights (p < .01), distance (.p

< .05), and significant interaction of approach lights with distonce (P. <

.05). Appreach angles were 0.22*higher on the average when approach lights

were not present. The significant main effect of distance was almost

entirely due to the Increase in approach angles with decreasing distance

from threshold when approach lights were present. Approaches made with

approach lights were 0.280lower Pt 20,000 ft and 0.12lower at 8,000 ft ftom

threshold than wheu approaches were made without approach lights. The main

effect of starting angle was also significant (p < .01) as was its

interaction with distance (p < .01). Approach angles were 0.220higher on

the average when the simulated approach angle was set at 3.00before the

start of a trial than when that starting angle was set at 0.50 . The effect

of starting angle was C.32cat the 20,000 ft distance and was reduced to 0.180

at the nearest distance.

w 2.5

_j

0

z

-)

0 w 2.0

x W

Wu 1.5F 0 WITH APPROACH LIGHTS

z 0 WITHOUT APPROACH LIGHTS

0.0 I_ I I I I

8,000 11,000 14,000 17,000 20,000

DISTANCE FROM THRESHOLD (FEET)

FIGURE 2. Mean approach angle in degrees as a function of approach

lighting and distance.

4
The variability of responses between subjects (intrsubject

vpriability) in a given experimental condition was lorge. The average

intersubject range of responses is shown in Table I as a function of

approach lighting and distance. Intersubject range varied inverse]y with

distance and tended to be about 0.8 0 higher in approaches made without

approach lights. The sane pattern of effects was apparent In the

Intersubject variances of responses which are shown in Table VII as a

function of approach lighting ond distance. An analysis of response

variability involving statistical comparison of variances could not be

performed on these data using the conventional F-ratio due to lack of

independence of scores. Statistical evaluation of intersubject variability

of responses with and without approach ights was, therefore, performed by

converting each generated approach angl., score to an absolute deviation from

the group mean for each condition (i.e., each combination of approach

lighting condition, starting angle, and dist,:nce). The effects of approach

lighting and distance on absolute deviations are described in Table III. An

analysis of variance of ab.solute deviation data indicated that there was no

significant effect of approach lig. ts on Intersubject variability. The only

significant effect was the main efiect of distance (2 < .01). Absolute

deviations increased with decreasng distance from threshold.

TABLE T. In~i:ubject Range in Degrees as a Function of

qpproach Lighting and Distance from Threshold

Approach Lighting .

Dis.auco No

(feet) ALSF-2 ALSF-2 Mean

8,000 4.10 9.i/4 4.72

11,000 3.75 4.66 4.21

14,000 3.44 4.15 3.PO

17,000 3.00 4.01 3.51 Aocossion For

20,000 3.01 3.23 3.12 NTIS QRA&I

DTIC TAB

Mean 3.46 4.2F Unannounced 0

Justification

By5 Distrlbution/

Availability Codes

Avail and/or

Z Dist Special
TABLE I. Intersubject Variances in Degrees as a Function of

Approach Lighting and Distance from Threshold

Approach Liphting

Distance No

.(feet) ALSF-2 ALSF-2 Mean

8,000 1.]F 1.02 1.10

13,C00 .95 .90 .93

14,000 .qe .76 .83

17,000 .84 .63 .74

20,000 .61 .53 .57

Mean .90 .77

TABLE III. Intersubject Variabtlity Measured with Absolute

Deviations (in Degrees) as a Function of Approach

Lighting and Distance from Threshold

Approach Lighting

Distance No

(feet) ALSF-2 ALSF-2 Mean

8,000 .85 .85 .85

11,000 .P0 .78 .79

14,000 .74 .78 .76

17,000 .68 .73 .71

20,000 .61 .64 .63

Mean .74 .76

6
Variability within the responses of an individual subject (intrasubject

variability) was assessed by using the difference score, or range, between

approach angles produced by a subject in the 0.5"Pnd 3.0starting angle

conditions in each approach lighting condition and at each distance.

Intrasubject range data are given In Table IV as a function of approach

lighting and distance. Intrasubject range was nominally higher on the

average in approaches made without approach lights than in approaches with

approach lights; means were 0.480and 0.350, respectively. Although the

effect of approach lighting on Intrasubject variability tended to vary

inversely with distance, an analysis of variance of intrasubjeCt range

scores revealed that neither that interaction nor the main effects of

distance or approach lighting were statistically significant.

Table IV. Intrasubject Range in Degrees as a Function of

Approach Lighting and Ditance from Threshold

Approach Lipihting

Distance No

(feet) ALSF-2 ALSF-2 Mean

8,000 .37 .37 .37

11,0()0 .36 .41 •

14,000 .35 .51 .43

17,t00 .29 .53 .41

20,000 .38 .57 .4P

Me.n 548

The relation of performance to the individual pilot's amount of flying

experience and the slze of aircrft he normally flew are also of interest.

For the present analysis flying experience was measured by the total hours

flown as pilot in commend and the size of aircraft flon was categorized as

li-hr, less than 12,50C lbs, or heavy, greater than 12,500 lbs. The apsects

o performance related to flying experience and aircraft size were (I) the

maean approach angle for each subject over all conditions of the experiment,

(,i) the difference between mean approach angles in approacb ligbtirg and no

apprcach lighting cond'tions, and (iII) intrasubject variability of each

subject as measured by the mean intrasubject range of responses over all

experimental conditions. The correlations of flying experience and aircraft

7
size with those performance measures A'e given in Table V. None of these

correlations was statistically signiitzant. The slight positive

relaticnship of flying experience with approach lighting effect (r .19)

and the slipht negative relationship of aircraft size with mean approach

angle (r - -.22) were the highest correlations observed.

Table V. Intercorrelacions of Pilot Experience, Size of

Aircraft Flown, and Subject Means for Generated

Approach Anples (All Conditions), Approach

Lighting Effect, and Intrasubject Range (N-40)

Approach

Aircraft Yean Lighting Intrasubject

Size Angle Effect Range

Total Flying Hosirs .25 .OF .19 -.02

Aircraft Size -.22 -.06 .11

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. The present experiment corroborates

previous findings regarding the tendency toward low approaches in the "black

hole" situation. The mean generated opproach angle over Qll subjects was

2.13 0without approach lights and 1.90 0 with approach lights. These values

are less than desired, and values as low as 0.6 occurrpd In approaches of

two pilots. Fourteen pilots had mean approach angles, averaged over all

conditions, of less than 1.5*. Low approach angles were generated in many

cases which could have been catastrophic in actual approaches. Although

some writers, mentioned above, have suggested that approach lights add

significantly to information for perception of approach angle, the present

experiment found that adding approach lights changed approach angles by only

0.2, and actually lowered approach angles instead of raising them toward

the desired level. Although that decrease In approach anrles when approach

lights were present was statistically significant, the magnitude of that

effect is only slightly larger thnn the error of measurement inherent in

measuring approach angle (0.10) and is small compared to both intra- and

intersubject variability of responses. This small negative effect of

approach lights is, therefore, probably not of practical significance for

perception of the magnitude of approach angle and is most likely offset by

the value of approach lights in other visual tasks performed during

npproaches such as identifying runway location, runway alignment, roll

guidance, and aimpoint estimption (1,7,8). The present finding also does

not eliminate th-o possibility that approach lights may enhance the

perception of approach angle magnitude at distances less than 8,000 ft from

threshold, the closest distance simulated here.

8
The low correlations of total flying hours and size of aircraft flown

with performance suggest that those two aspects of pilot experience were of

relatively low importance In determining perception of approach angle in the

present simulated approach situptions. This issue is discussed further in

the context of Experiment II below.

Both intersubject and intrasubject variability were lower when approach

lighting was present. Althougb those effects were not statistically

significant, response variability should receive attention in future

research in terms of the possible ability of approach lighting to prevent

oscillating, unstable approaches which could be as dangerous, or perhaps

more dangerous than low stable approaches, especially in the nighttime

"black hole" situation.

EXPERI|IENT II

Experiment IT had two purposes: First, the potential interaction of

visual information from approach lighting with an illusion involving

variation in runway length was examined. Second, the effect of approach

lights was evaluated as a function of variation in approach light intensity.

Overly bright, glaring approach lights would be expected to reduce

informarion in the runway scene by making details of both approach and

runway lighting less visible. That might decrease illusions due to varying

runway length or increase variability of responses. Experiment II also

utilized a different approach light system. Whereas Experiment I simulated

the largest system (3,000 ft), Experiment II simulated one of the smallest

(1,400 ft). This modification permits study of length of approach light

system as a factor.

Method.

Subjects. Twenty-four pilots who had participated in Experiment I were

randomly selected to participate in Experiment II. There was an interval

between experiments of at least 3 weeks. This group had the same range of

flying experience as did the original group in Expe iment I and had a median

experience level of 1,600 hours with a semi-interquartile range of 1,900

hours. Nine were pilots of heavy aircraft and 15 were pilots of light,

single and twin engine aircraft.

Apparatus. The apparatus wac identical to that used in Experiment I

with the exception that a short (1,400 ft) simplified approach light system

(SSALS) was simulated. To achieve both variable intensity and as high an

intensity as possible, 0.030 in diameter incandescent Pinlites (Model

L15-45, REFAC Electronics Corporation, Winsted, Connecticut) were used to

make individual lights of the simulated approach light system. Runway

lights were wodeled as before (Experiment I) using the fiber optic

technique. The incandescent approach lights were powered by a regulated

adjustable DC power supply which was set with the aid of a digital voltmeter

I9
to achieve the simulated luminous intensity for individual approach lights

of 120 and 2,500 candelas in addition to 0 candelas, or "off." Runway light intensity was always 120 candelas. The runway simulated was 150 ft by 6,000

ft with edge and end lighting only. When appropriate, the lights of the upwind half of the runway were covered with black velveteen to reduce the

visible length of the runway to 3,000 ft.

Procedure. The subject's task was again to control the runway model as it moved toward him in order to produce the same "normal" approach angle on

every trial. Viewing conditions, range of simulated distances, and

simulated approach speed were the same as in Experiment I.

After four practice trials with a 150 ft by 6,000 ft runway without

approach lights, the six combinations of three approach light intensities

(0, 12C, and 2,500 candelas) and two conditions of visible runway length

(full 6,000 ft runway visible in one condition; lights of the upwind half cccluded in the other condition) were presented. Each condition of approach light intensity and visible runway length was also presented with three

starting angles, 0.5 3.C¢ and 5.50 . The IP combinations of approach liglt intensity, runway visibility, and starting angles were presented in random

order. No feedback concerning performance was given during the experiment. Experimental sessions lasted approximately 2 hours for each subject.

Results.

The effects of approach lights, visible runway length, starting angle, and distance on generated approach angles were analyzed with analysis of variance for repeated measures. The significant main effects of approach lighting (p < .01) and visible runway length (p < .01) are illustrated in Figure 3. Their interaction was not significant. Mean approach angles were

about 0. 5higher when only half the runway was visible. The effect was similar at all intensities of approach lighting. With a particular visible

runway length, iean approach angles were sim, nr when approach lights were

turned off (zero intensity) and when their intensity was 20 times that of

runway lights. When approach lights had intensity equal to runway lights, the presence of approach lights caused approach angles to average about 0.1

less when the full 6,00 ft runway was visible and about 0.2aless when only half the runway was visible. There was no significant Interaction of either

approach light intensity or visible runway length with distance.

, 10
3.0

W

z

0 w 2.5

0- (D 0

00

. 2.0 1/2 RUNWAY VISIBLE z

W 0 FULL RUNWAY VISIBLE

0.0 f I I I

0 120 2,500

INTENSITY (CANDELAS)

FIGURE 3. Mean approach angles in degrees as a function of

approach light intensity and visible runway length.

W

-J 3.0-

z

4

WC

(fL or W STARTING ANGLE

FIGURE~~~ 0.5* untono
Both the main effect of starting angle and the interaction of starting

angle wfth distance, which are illustrated In Figure 4, were statistically

significant at the p < .01 level. The magnitude of the effect of starting

angle decreased from approximately 0.8"at 20,000 ft to 0.20at 8,000 ft from

threshold.

The great variability of responses between subjects was again an

important finding. The average range of responses between subjects over all

conditions was 4.40 . Intersubject range is shown in Table VI as a function

of approach light intensity, visible runway length, and distance. There was

a tendency for intersubject range to vcty inversely with distance and

visible runway length. Intersubject range was also slightly lower (4.060)

when equal intensity approach lights were present than when approach lights

were either not visible (4.46*) or when approach lights were 20 times as

bright as runway lights (4.560). The same pattern of effects was apparent

in the intersubject variances of responses which are shown In Table VII as.a

function of approach lighting intensity, visible runway length, and

distance.

TABLE VI. Tntersubject Range In Degrees as a Function of

Approach Lighting, Visible Runway Length, and

Distance from Threshold

SSALS Runway Distance from Threshold (feet)

Intensity Length

(Candelas) (feet) LM 11,000 14,000 17)00 20.000

0 3,000 6.1? 5.38 5.02 4.57 4.15

6,000 4.51 4.24 3.99 3.41 3.15

3,000 5.66 4.92 4.39 4.06 3.65

120

6,000 4.43 2.17 3.47 3.15 3.14

3,000 6.25 5.41 4.68 4.14 3.94

2,500

6,000 5.54 4.70 3.91 3.69 3.30

12
TABLE VII. Intersubject Variance In Degrees as a Function of

Approach Lighting, Visible Runway Lpngth, and

Distance from Threshold.

SSALS Runway Distance from Threshold (feet)

Intensity Lengtb'

(Candelas) (feet) 8,000 11,000 114,000 !,000 20,000

3,000 2.19 1.85 1.77 1.79 1.43

0

6,000 1.09 1.03 1.00 0.93 0.92

3,000 1.86 1.61 1.34 1.23 0.97

120

6,000 1.16 0.89 0.88 0.81 0.79

3,000 2.11 1.72 1.49 1.26 1.18 ~2, 500

6,000 1.54 1.21 1.06 0.96 0.91

Intersubject variability was evaluated statistically, as in Experiment

1, by converting each generated approach angle score to an absolute

deviation from the group mEan for each condition (i.e., each combination of

approach light intensity, visible runway length, starting angle, and

distance). These data were analyzed by analysis of variance. The only

significant effect revealed was the main effect of visible runway length.

Absolute deviations are shown in Table VIII as a function of visible runway

length and distance. Although the effect of distance on intersubject range

was large, the effect of distance on intersubject absolute deviations was

not statistically significant. The large intersubject range uf responses

between subjects in all conditions remains a most important finding in these

data.

Intrasubject variability was assessed using the range of scores over the three starting angles in each condition of approach lighting intensity,

visible runway length, and distance. The average intrasubject range within

a particular combination of approach light intensity, visible runway length,

and distance was 0.850. Intrasubject range data are given in Table IX as a

function of approach light intensity, visible runway length, and distance.

13
Effects of all variables were small and the only statistically significant

effect (p < .01) in these data was the efffect of distance.

TABLE VIII. Intersubject Variability Measured with Absolute

Deviations (in Degrees) as a Function of Visible

Runway Length and Distance

Runway Distance from Threshold (feet)

Length

_(feet) LM 11,000 14,000 17,000 20,000

3,000 1.04 1.00 0.97 0.95 0.83

6,000 0.83 0.78 0.76 0.74 0.70

TABLE IX. Intrasubject Range in Degrees as a Function of Approach

Lighting, Visible Runway Length, and Distance from

Threshold

SSALS Runway Distance fro' Threshold (feet)

Intensity Length

(cdjas) (fet) ,000 11,000 14,000 17,000 2

3,000 0.93 0.94 0.90 1.15 2.10

0

b,000 0.71 0.69 0.75 0.86 1.07

3,000 0.80 0.72 0.63 0.74 0.99

120

6,000 0.62 0.69 0.80 0.80 0.99

3,000 0.79 0.80 0.82 0.90 1.18

2,500

6,000 0.65 0.58 0.65 0.85 1.05

14
The relation of performance to the individual pilot's amount of flying

experience (total flying hours) and the size of aircraft he normally flew

(heavy vs. light) was evaluated, as in Experiment I, by correlating those

experience factors to (i) the overall mean approach angle for each subject

(i) the approach lighting effect (i.e., the difference between mean

approach angles in the 0 and 120 candele approach ligbting intensity

conditions), and (Ili) the intrasubject variability of each subject as

measured by the mean Intrasubject range for each subject. Those drta are

shown In Table X. The correlations of total flying hours with performance,

in this subgroup of the 40 pilots who participated In'Experiment i, were

again not statistically significant, but the correlation of flying hours

with mean approach angle (r-= .36) was greater than the corresponding value

(r = .OP) for all 40 subjects in Experiment I. The negative correlations of

aircraft size with mean approach angle and approach lighting and

intrasubject effect were also larger in Experiment II, with statisticpl

significance (p < .05) occuring in the correlations of aircraft size with

mean approach angle (r = -. 42) and aircraft size with approach lighting

effect (r - -.41). These two correlations indicate trends Involving lower

approach angles for subjects who were pilots of larger aircraft and smaller

decreases in approach "ngle in that group as a function of the presence of

approach lights with Intensity equal to runway lights.

TABLE X. Intercorrelations of Pilot Experience. 'ize of

Aircraft Flown, and Subject Yeans for G, ted

Approach Angles (All Conditions), Approach

Lighting Effect, and Intrasubject Range (N=24)

Mean

Aircraft Approach ALS Intrasubject

Size Angle Effect Range

Total Flying Hours .122 .35F -.046 -.019

Aircraft Size -. 424 -. 410 -. 246

Discussion.

The effect of SSALS approach lights was a small but statistically

significant decrease in mean generated approach angles, about 0.20, in

agreement with the effect of the ALSF-2 system studied in Experiment I.

Arguments concerning the lack of practical significance of the effect of

equal intensity approach lights given in the discussion of Experiment I also

apply to the findings of the second experiment.

The effects of equal intensity SSALS lighting again decreased both

intra- and intersubject variability of responses slightly, but not at a

statistically significant level. Examination of raw data revealed that the

tendency toward reduction of variebility in both experiments was due to

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lowerinp of responses in the high end of the response distribution without

raising responses in the extreme low end of the distribution. Since it is

the lowest approach angles that are of greatest concern for aviation, the

effects of approach lighting on response variability, as in the case of

effects or mean responses, may not be of practical significance at the

distances studied here. The finding of nominally lower response variability

when approach lighting was present was, however, consistent in two

experiments. It is suggested that the effects of approach lighting on

stabi]iry of approaches should be reexamined In future experiments dealing

with shorter distances from threshold than the minimum 8,000 ft of the

present experiments. At distances from threshold less than 8,000 ft, the

danger potential of oscillating, unstable approaches would be greater, and

the benefit of reduction in response variability due to approach lighting

may also be greater.

The fact that the presence of the SSALS had a lesser effect when the

full runway was visible than when half the runway was visible suggests that

the effect of approach lighting may vairy with the ratio of the lengths of

approach and runway lighting. Two additional findings support this

suggestion. First, both the ALSF-2 and SSALS, which differ greatly in

length, produced approximately the same magnitude of effect (0.240and 0.200

respectively) when the approach/runway length ratio was approximately the

same. Second, the effect of adding the 3,000 ft ALSF-2 to the 6,000 ft

runway produced an effect similar in m.-gnitude to the effect of increasing

runway length from 6,000 ft to 9,000 ft in another experiment (6). Although

the effects of approach lighting on perception of approach angle in the

present study were of doubtful practical significance, it is possible that

* larger effects might be generated with higher retios of approach lighting

length to visible runway length. Higher ratios might be encountered when

fog reduces the visible runway length to lesser values than studied here,

and would be most likely to occur with the longest (2,400 ft and 3,000 ft)

approach light systems.

The affect of making approach lights 20 times brighter than runway edge

3i g.t.s was to elniriat th biall decrease in mean approach angle that

occurred with equal Intensity approach lights. Pean approach angles

increased at the highest approach light intensity, as did both intra- and

intersubject variability, to the same levels that occured when approach

lights were turned off. Although the high level of intensity used here did

not Ocrease performance relative to the no approach light condition, it is

likely that higher levels of intensity would. It is apparent that although

the glare was uncomfortablo (but not painful) in the present situation when

the model was at nearer distances, the glare did not eliminate the important

information for judgment of approach angle in the runway image. Since

pilots normally have the ability to request changes In approach light

intensity, it is not likely that higher glare levels would be tolerated in

visual approaches.

The finding of low correlations of total flylig hours with performance

in both Experiments I and IT suggests a relatively low importance of that

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factor in determining perception of approach angle. The finding of

statistically significant correlations between the type of aircraft flown

with both mean approach angles generated and the magnitude of effect of

approach lighting in Experiment II indicates greater importance of that

factor. The significant negative correlation of type of aircraft flown by a

pilot with the overall mean approach -ngle produced by that pilot may be

explained by the fact that pilots of heavy aircraft normally fly lower

approach angles than do pilots of light aircraft. Visual Approach Slope

Indicators (VASI) and Instrument Landing Systems (ILS) at airports servicing

heavy aircraft frequently have those systems set to produce lower angles of

approach. For example the majority of pilots who flew heavy aircraft in

this experiment flew heavy multiengine turbojet aircraft at a local military

base where VASI and ILS aids were set to generate 2.5Dapproach angles. In

contrast, pilots of light aircraft in this study flew from local airports

where those aids were set to generate 3*appropch angles. In addition, the

negative correlations of type of aircraft flown with magnitude of approach

lighting effects may reflect greater recent experience of pilots of heavy

aircraft in flying approaches with approacb lighting systems pisent. This

suggested importance of recent experience in flying Visual approaches is

supported by findings of a previous study by Pertens and Lewis (6). That

earlier work demonstrated that approach angles to a particular size of

runway were higher when preceded by practice with a wider or shorter runway

and lower when preceded by practice with a more narrow or longer runway.

The findings of the above mentioned studies raise the question of whether or

not the ability to make visual judgments of approach angle deteriorates as a

function of time following practice in visual approaches. Future research

on factors affecting the transfer of previous experience in visual

approaches to subsequent approaches is needed.

The major finding of this study was that the visual Information added

to the nighttime visual approach scene by approach light systems did not

have effects of practical significance on perception of approach angles at

distances from runway threshold of 8,000 ft and greater. The presence of

approach lighting did not reduce the tendency to overestimate approach angle

and produce low approaches in the "black hole" situation and did not reduce

illusions occurring as a result of differences in runway size. Statements

in the literature that approach light systems do provide information for

perception of approach angle magnitude, therefore, do not appear to be

correct over the distance range studied here. The possibility that approach

lighting may provide important information for perception of approach anglc

magnitude in the approach segment between 8,COO ft and thresheld should be

examined in future research. The value of approach lighting In other tasks

performed during visual approaches such as identifying runway location,

runway alignment, roll guidance, and aim point estimation, as mentioned

above, makes approach lighting highly desirable, but the presence of

approach lighting should not decrease the pilot's concern about illusions in

"black hole" approaches which could lead to acceptance of dangerously low

approach angles.

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The present results corroborate previous findings regarding significant

effects of runway length on perception of approach angle. These findings

suggest that change in length of the visible segment of the runway due to

fog may also have an effect on perception of approach angle. In that case,

cues involving the variation of intensity with distance would also be

affected by fog and may interact in the cues involving visible length.

Future research on the effects of adverse weather involving reduced

visibility should consider this interaction. Pilot training should also be

developed to help pilots counteract visual illusions due to variation in

runway width and variation in runway length, including reduction of visible

runway length due to adverse weather.

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REFERENCES

1. Iwataki, N., and H. Kansaku. 1973. Visual considerations concerning

approach lights. Report No. NASA TT F-14, 667, National Aeronautics

and Space Administration, Washington, D.C. (translation).

2. Lewis, M. F., and H. W. Mertens. 1979. Pilot performarce during

simulated approaches and landings made with various computer-generated

visual glide-path indicators. Aviat. Space and Environ. Med. 50:991-1002.

3. Mertens, H. W. 1977. Laboratory apparatus for studying visual space

perception of the pilot in simulated night approaches to landing.

Percept. Mot. Skills, 45:1331-1336.

4. Mertens, H. W. 1978. Comparison of the visual perception of a runway

model in pilots and nonpilots during simulated night landing approaches.

Aviat. Space and Environ. Med. 49:1043-1053.

5. Mertens, H. W. 1981. Perception of runway image shape and approach

angle magnitude in pilots in simulated night landing approacheAviat. Space and Environ. Med. 52:373-386.

6. Mertens, H. W., and M. F. Lewis. Effect of different runway size on

pilot performance during simulated night landing approaehes. Aviat.

Space and Environ. Med., in press.

7. U-S. Government. 1969. Handbook: Visual Guidance Lighting Systems.

Advisory Circular No. 6850.2, Federal Aviation Administration, Department of Transportation, Washington, D.C. (p.2).

8. Wulfeck, J. W., A. Weisz,and M. W. Raben. 1958. Vision in Military

Aviation. Technical Report No. 58-399, Wright-Patterson Air Development

Center, Air Research Development Command, Wright-Patterson AFB, Ohio,

(pp. 263-266).

*U.S. GOVERNMENT PRINTING OFFICE: 1982 369-486/728 1-3

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