The results of the questionnaire indicate that
aircraft instruments with many numerals and
markings (airspeed indicator and altimeter) re-

quire optimum visual acuit

y for proper interpre-
tation.

However, one-third of the pilots reported
that an instrument with few numerals or mark-
ings (attitude indicator) required optimum
visual acuity for proper interpretation, The
apparent dichotomy of opinions indicates that
interpretative difficulties associated with dial de-
sign may influence the pilots opinions. In addi-
tion, we believe that the pilot’s training and
experience influence his opinion about the Instru-

Inents that require optimum vision for correct
dial interpretation,

The readability for electro-optical displays
(cathode ray, light-emitting diode, etc.) was not
covered in the questionnaire. Because of increas-

ing use of these displays in aircraft instruments,
further research is recommenced

with respect to older pilots.

To isolate visual performance from the pilots’
subjective judgment, we recommend a
evaluate readability of airer

der various visual acuity

in this area

stucly to
aft instruments un-
levels and flying con-

Instrument-readability problems caused by
oblique observation anges (parallax) also merit
Investigation as to their significance and possible
remedies by design modification,

Nearly half the respondents indicated that jn-
strument readability was a problem when flymg
at night. We believe that further research is
necessary concerning the effects of instrument
lighting intensity, spectral color of lighting, dial
markings, hypoxia, fatigue, and drugs with re-
spect to night vision in older pilots. Several

papers direct attention to the visual problems of
presbyopic pilots,1% 20 21

The trifocal portion of a spectacle lens is de-
signed to improve visual acuity at the inter-
mediate (instrument panel) range. The necessity
for trifocal lenses increases with age and is con-
sidered essential to provide good intermediate
vision for those with less than 2.00 D of accom-
modation. Data show that individuals 53 years

of age or older have less than 2.00 D of accom-
modation and may benefit from trifocal lenses,
especially under dim luminance conditions. §

ditions. Information concerning the visual,

cognitive, and design aspects of instrument read-
ability is found in several sources.1% 17 18

Another: visual problem noted by one-third of
the pilots was reflective glare from the glass
plates covering the panel instruments. Reflective
glare is presumed to occur without respect to the
pilot’s age or visual status. At least two aspects
of cover plate reflections require further investi-
gation. First, research should be conducted to
quantitate visual impairment caused by reflee-
tions during various flight conditions,
we need data on the effectiveness of sh
lighting, polarizing
cover plates,

Second,
ielding,
, and/or convexing the glass

However, of the 14 pilots more than 53 years of
age surveyed in our study, only two pilots wore
trifocal lenses. Harper and Kidera also reported
that many senior pilots flying large commercial
aircraft do not wear trifocal lenses.*° They
stated that natural human reluctance to we

multifocal Jenses and unawareness of pr
Intermediate visual acuity
factors.

airing
educed
were contributing

This survey revealed several potential visual

problems common to older general aviation

pilots. We feel that these visual] problems merit
further attention with respect to medical stand-

ards, accident statistics, human factors,

ancl
cockpit design.

11. W!
Pdi
Pu

12. Oh
AS
416.


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isual
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had
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said
Lime

from outside the cockpit to charts and 17 percent
had noticed an increase in focusing time from
outside to the instruments. Few pilots (6 per-
cent) reported a delay in focusing from maps
or instruments to outside the aircraft.

Frequency of Problems. When the pilots were
asked if they had noted any difficulty in reading
aircraft instruments, 56 percent reported none,
88 percent said “occasionally,” and 6 percent re-
ported frequent visual problems. When ques-
tioned as to when the instruments are most
difficult to read, 48 percent indicated “nighttime,”
28 percent said “dawn and dusk,” 22 percent
replied “never difficult,” and 6 percent reported
“equally difficult at all times.” Of the 16 pilots
reporting visual difficulty from reflective glare
off the instrument cover plates, 69 percent indi-
cated more problems during the day while 31
peréent had more problems at night.

Individual Solutions. Table 3 lists the sub-
jects’ responses concerning various methods usecl
to improve the readability of the cockpit instru-
ments.

TABLE 3.

Methods Used by Pilocs
to Improve Instrumenc Readability

Move head/body
Methods

Used Shield outside lighe

Response (Percent)

When asked what specific steps were taken to
reduce reflections from the glass cover plates, 43
percent stated they employed head movements
and 26 percent shielded the instruments; the re-
maining subjects gave no response.

Of 44 pilots responding to the question con-
cerning the level of instrument brightness pre-
ferred during night flying, 66 percent preferred
the medium intensity level, 23 percent liked the
brightest level, and 16 percent preferred the dim
level. Thirty percent of those responding stated
they occasionally used a flashlight to read the
instruments when flying at night. When asked

to recommend changes to improve the readability
of aircraft instruments, 36 percent recommended
lighting changes, 28 percent indicated changes
in the dial design, and 30 percent said no changes
were needed.

Miscellaneous Data. Prescription spectacle
lenses were worn by 68 percent of the subjects
while flying. Of those wearing glasses, 67 per-
cent wore bifocal lenses, 27 percent wore trifocal
lenses, and 7 percent wore half-eye reading
glasses. When viewing the instruments, 65 per-
cent of those wearing bifocal lenses used the
bifocal (lower) portion rather than the distance
portion of the lens. Sixty-two percent of the
trifocal wearers used the trifocal (middle) por-
tion of the lens to view the instruments. Of
those pilots wearing glasses, 44 percent carried
an extra pair while flying.

Information from the Aeromedical Certifica-
tion Branch showed that 82 percent of all pilots
are required to wear glasses while flying. An
additional 8.2 percent of the pilots must have
glasses (usually the reading type) available
while flying. Although the information was not
available, the percentage of pilots wearing glasses
would be expected to increase with age.

In response to the question concerning the
color of instrument lighting available, 52 percent
of the subjects stated they flew aircraft equipped
with red panel lighting, 24 percent said white
lighting, while 22 percent said selectable red or
white lighting.

LV. Discussion.

Because of the limited pilot population sur-
veyed (N=50) and the large number of ocular
refractive and instrumentation variables, no
statistical correlations could be made between the
visual measurements and questionnaire data.
However, in a laboratory study now in progress
at the FAA Civil Aeromedical Institute, visual
acuity of older subjects will be determined
through the distance and near portions of their
spectacle lenses at 51, 76, and 102 cm during
photopic viewing conditions, The questionnaire
data, however, indicate several common instru-
ment-readability problems among older pilots.
Although not investigated in this study, many
of the same problems may also occur among
younger pilots when flying under similar cond-
tions.


in cused by

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| ]) of ieeeom-
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They
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factors, and

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10.

11,

12,

References

Parke, R. B.: Editorial, FLYING, 99:2, 18, 1976.

Turner, M. J.: Observations in the Normal Subjec-
tive Amplitude of Accommodation, BR. J. PHYSIOL.
OPT., 15:70, 1958.

Hamasaki, D., I. Ong, and HE. Marg: The Amplitude
of Accommodation in Presbyopia, AM, J. OPTOM.,
83:8, 1056.

. Hofstetter, I. W.: A Comparison of Duane’s and

Donders’ Tables of the Amplitude of Accommoda-
tion, AM. J. OPTOM., 21:9, 1044.

. Diamond, 8.: Effects of Red Lighting on Accom-

modation in Aircrew Personnel, AEROSP. MUD.,
34 :1005-1007, 1963.

. McFarland, R. A., R. G. Domey, A. B. Warren, and

D. C. Ward: Dark Adaptation as a Function of Age,
J. GERONTOL., 15 :149-154, 1960.

. Guth, S. K.: Effects of Age on Visibility, AM. J.

OPTOM., 84:9, 468-477, 1957.

Mourant, R. R., and G. D. Langolf: Luminance
Specifications for Automobile Instrument Panels,
HUM, FACTORS, 18:71-84, 1976.

. Walton, W. G.: Visual Problems of the Institutional

Aged, AM. J. OPTOM., 44 :319-335, 1967.

Weymouth, F. W.: Effect of Age on Visual Acuity.
In M. J. Hirsch and R. W. Wick (Ed.): Vision of
the Aging Patient, Chilton Co., Philadelphia, 1960.
Whiteside, T. GC. D.: The Problems of Vision im
Flight at High Altitudes, Butterworth’s Scientific
Publications, London, 1957.

Ohlbaum, M. K.: The Effects of Hypoxia on Certain
Aspects of Visual Performance, AM. J. OPTOM.,,
46:4, 285-249, 1969.

13.

14.

15.

16.

1%.

18.

TD,

20).

21,

McFarland, R. A. M. H. Halperin, and J. I. Niven :
Visual Thresholds as an Index of Physiological Im-
balance During Insulin Tfypoglycemia, AM. J.
PHYSIOL., 145 :299-318, 1946.

MeFarland, R. A., F. J. Roughton, M. FI. Halperin,
and J. I. Niven: The Effects of Carbon Monoxide
and Altitude on Visual Thresholds, J. AVIAT. MED.,
15 :881-894, 1944.

Luria, S. M., Hl. M. Paulson, J. S. Kinney, C. IL.
McKay, M. §. Strauss, and A. P. Ryan: The Hffect
of Common Therapeutic Drugs on Vision, U.S. Navy,
Bureau of Medicine and Surgery, Work Unit
]4305.08-3001.11, Report No. 808, 1975.

Wulfeck, J. W., A. Weisz, and M. W, Raben: Vision
in Military Aviation, Wright Alr Development Cen-
ter Technical Report 58-899, Wright-Patterson Air
Force Base, 1058.

Kappaut, W. E.: The Design and Use of Instru-
ments. Jn National Research Council: Human
Factors in Undersea Warfare, Washington, D.C.,
1949,

Van Cott, H. P., and R. G. Kinkade (Hd.): Human

Engineering Guide to Hquipment Design, U.S. Gov-
ernment Printing Office, Washington, D.C., 1972.

Backman, EL, and F, D. Smith: The Design and
Preseription of Multifocal Lenses for Civil Pilots,
AM. J. OPTOM., 52 :501-599, 1075.

Harper, GR, and G, J. Kidera: Flight Deek Vision
and the Aging Eye, AEROSP. MED., 39 11119-1122,
1968.

Cox, B. J. and G. A. Bastedo: Visual Problems of
Airline Pilots, CAN. J. OP'TOM., 26:2, 3-6, 1964,


Technical Report Documentation Page

1. Report No. 2. Government Accession No, 3. Recipient's Catalog No.
FAA-AM~7 7 -2
4. Title and Subtitle — 5, Report Date

SURVEY OF COCKPIT VISUAL PROBLEMS OF SENIOR PILOTS

6. Performing Organization Code

Performing Organization Report No.

| 7. Author's) | |
Kenneth W. Welsh, John A. Vaughan, Paul G. Rasmussen

9. Performing Organization Name and Address 10. Wark Unit No. (TRAIS)
FAA Civil Aeromedical Institute

P.O. Box 75082 ll. Contrect or Grant No. |

| Oklahoma City, Oklahoma 73125 po
13. Type of Report ond P |

eriod Covered
12. Sponsoring Agency Name and Address |
Office of Aviation Medicine | OAM Report |

Federal Aviation Administration | |

800 Independence Avenue, S.W. 14, Sponsoring Agency Code |
Washington, D.C. 20591 |

| 15. Supplementary Notes

| Work was performed under Task AM-D-76-PHY-91.

16. Abstract

Fifty general aviation pilots (average age 49; range 40-73) completed a question-
| naire concerning cockpit visual problems. The results of the questionnaire indicate
| that proper interpretation of the airspeed indicator and the altimeter required the
best visual acuity (48 and 39 percent of the respondents respectively). However,
33 percent reported the attitude indicator, an instrument with relatively few
numerals or markings, required optimum visual acuity. Thirty-seven percent of the
pilots reported that the engine instruments, usually smaller scale, are difficult
to read. Light reflected from instrument cover plates caused visual problems for
32 percent of the pilots, with most difficulty occurring during daylight hours.
Forty-eight percent of the pilots reported a delay in focusing from outside the |
cockpit to the charts and instruments, while 6 percent reported a delay of focusing
from inside to outside the cockpit. More instrument readability problems were
evident while flying at night than during’ dusk or daylight. The effects of
decreasing focusing power, altered dark adaptation, and need for more lighting are
discussed with respect to the older pilot. Recommendations are made to investigate
| the effects of instrument lighting, vision standards, and instrument design anc
| location with respect to the limitations of the aging visual system.

pe
17. Key Words 18. Distribution Statement
| Vision, Senior Pilots, Instrument | Document is available to the public |
| Readability through the National Technical Information
| Service, Springfield, Virginia 22151.

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

Unclassified Unclassified

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

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SURVEY OF COCKPIT VISUAL PROBLEMS OF SENIOR PILOTS

I. Introduction.

Tt is estimated that production of general
aviation aircraft will double in the next decade.
Most of these aircraft will be equipped for 1n-
strument flight.1 The population of general
aviation pilots is expectecl to increase commen-
surately. We can certainly expect to see greater
numbers of pilots in their sixties and seventies
flying aircraft and operating other types of ve-
hicles.

Aviation safety is partly dependent on the
pilot’s ability to read quickly and accurately
various cockpit instruments. Table 1 lists sev-
eral primary factors that may affect. the read-
ability of aircraft instruments. Each of the four
primary factors is dependent on several compo-
nent factors that may act singly or in combina-
tion for each individual and viewing situation.

Several well-known relationships exist between
chronological age and the capabilities of the
visual system. For example, the ability to focus
on near objects decreases with age.** Hofstetter
determined that accommodative amplitude de-
creases by 0.80 diopter (D) per year up to the
age of 60, after which approximately 0.50 D of
accommodation remains. An investigation by
Diamond indicates that accommodative ampli-
tude decreases more under dim red than under
dim white Lehting.®

Decreased accommodation causes blurred vi-
sion, with the effect beginning at the near range
(30 to 51 em) and later in life at the interme-
diate range (61 to 76 cm). Bifocal or trifocal
lenses are then required to correct visual acuity
at the near and intermediate ranges respectively.
In addition, the size, shape, and height of the
bifocal or trifocal segment limits the range over
which the eyes may scan.

Another visual process that deteriorates with
age is the capacity of the eye to adapt to dim
lighting. McFarland e¢é al. found that visual
sensitivity to a stimulus light decreased progres-
sively for each decade for subjects ranging in

TABLE 1.

Factors Influencing Instrument Readability and Flying Performance

Primary Factors Component Factors

yg ER Ly EE Ta

Refractive Error

Accommodation
Adaptation

| Oculomotor Disturbance

ee Se

Visual

re

Interpretative Skills
Emotional Status
Reaction Time
Experience

Training

es

General Health
Ocular Health
| Fatigue

Drugs

es

Digit Size
Contrast Ratios
| Lighting

View Distance
Parallax

Psychasensory

Biomedical

Display

Glare

Hypoxia

j Vibration
Toxic Products

Environmental

age from 16 to 89 years.’ Guth found that indi-
viduals in their sixties required twice as much
light as 20-year-olds to read printed words.’
However, a study by Mourant and Langolf indi-
cated that elderly individuals required 10 times
more light than did young people to obtaim 95-
percent-correctness scores for a symbol read-
ability task.® In addition, visual acuity of elderly
individuals may decline because of retinal
changes and clouding of the ocular meclia,® *°

Further degradation of several visual func-
tions occur under conditions of hypoxia. Mc-
Farland, Whiteside, and Ohlbaum found
(lecrements in several visual functions durmg
oxygen deprivation although the effect of age on


visual performance was not investigated.® 1”
Decrements in visual performance were also
noted for subjects with hypoglycemia or follow-
ing inhalation of carbon monoxide in small

quantities,* 4 Luria e¢ al, using therapeutic
(loses of five widely used medicinal drugs, found
changes in ocular pursuit movements, pupil size,
EEG, and recovery from a light flash although
changes with respect to age were not evaluated.

Because elderly pilots usually have known
visual limitations in the near and intermediate
ranges, a questionnaire was completed by, and
brief visual evaluation was conducted on, 50
pilots above the age of 40 years at an Oklahoma
fly-in held in the fall of 1975. Results of the
study provide information needed for the estab-
lishment. of priorities and guidelines for future

research related to intermediate vision and avia-
tion safety.

II. Methods.

Four women and 46 men volunteered to com-
plete the questionnaire and to participate in a
short. visual evaluation. The mean age of the
Stroup was 49.2 years (range 40-78). Thirty-
eight held private pilot certificates, 14 held com-
mercial pilot certificates, and 8 had airline
transport pilot certificates. Nineteen were jn-
strument rated, 11 had flight instructor airplane
(CFIA) ratings, and 8 held flight instructor
instrument (CFII) ratings. The mean flying
time for the group was 3,182 h (range 30-29,000
h) and all but four had some flight time the
previous year (mean 77 h).

A battery of visual measurements was made
on each pilot with the Titmus Vision Tester,
Aeromedical Model. The tests included the sub-
ject’s near and distant visual acuity, ocular
muscle balance, and color vision. In addition,
tests were made for intermediate visual acuity
(76 em), amplitude of accommodation (RAF
Rule), and the subject's spectacle lens preserip-
tion. Data from the visual portion of the study
are not Included in this report but are available
on request. The results were not included be-
cause the subject population was relatively small,
subjects’ ocular statuses varied widely, and sev-

eral volunteers did not have their
contact lenses,

glasses or wore

III. Results.

Most of the questions were multiple choice,
and several allowed the subjects to select more
than one response. The remaining questions re-
quired a short written statement.

Snecific Visual Problems. Table 2 shows the
various responses given to the question concern-
ing the primary flight instruments (altimeter,
airspeed, attitude) requiring optimum visual
acuity for proper interpretation. Several sub-
jects noted more than one cockpit instrument.
Also given in Table 2 are the subjects’ responses
to other panel instruments that, in their opinion,
require optimum visual acuity.

TABLE 2,
Subject Response (%) as to the

Instruments Requiring the Rest
Visual Acuity for Proper Interpretation

Airspeed Indicator

Primry
Fliphe Altimeter
Instruments
Attitude Indicator
Directional Gyro
Turn and Slip
Engine Instruments
Other
Panel Tachometer
Instruments

Magnetic Compass

. None

10 40 50
Response (Percent)

When asked whether reflections from the glass
plates covering the instruments hampered vision,
68 percent responded “no” and 32 percent re-
sponded “yes.” As to other factors that ad-
versely affected the readability of aircraft.
instruments, 18 of 20 pilots responded that in-
struments having small numerals were difficult
to read, while 7 of 20 indicated that visual
parallax was a problem for instruments in the
central portion of the panel. To observe the
instruments in the central portion of the panel,

the pilot in the left seat must look to his right
at an oblique angle.

When the pilots were asked whether they had
noticed over the years any alteration of time
required to change visual focus, 81 percent said
they had noticed an increase in focusing time

ft
hi
ol
ce
al