Ficure 8. Portable, seven-channel tape recorder used
to obtain in-flight pilot performance data during simu-

lated instrument approaches. Arrow indicates meter
panel for monitoring inputs to recorder.

Data Recorded

Data recorded during the flights consisted of
vertical deviation of the aircraft relative to the
glide slope centerline; lateral deviation to either
side of the localizer centerline; aircraft bank
angle; vertical acceleration of the aircraft ; heart
rate of the pilot-subjects; and “event” informa-
tion such as passage over geographical “fixes”,
calibration checks and observer’s comments.
However, only heart rate data were used for this
report.

Subjects

Eight of forty pilots volunteering for the pri-
mary (aural glide slope) study were chosen as a
control group. To obtain these eight (Table 1),
the original forty pilots (all of whom possessed
current FAA Airman Medical Certificates and
FAA Instrument Ratings) were ranked from
“high” to “low” on the basis of their number of
hours of instrument flight experience. Some ar-
bitrary weight was given to recency of experience
and total flying hours for those subjects reporting
approximately the same level of instrument ex-

Taste I.—Age, experience, and ratings of subjects
participating as control group for master study: and
for which heart rate data is presented in this report.

Ages are given to nearest bitthday.

Total instrument hours include simulator training.

Sub- Total | Total | Com- Flight
ject | Age | flight | instru-| mer- | ATR | instru-
num-|(Yrs.)| hours | ment | cial | rating | tor
ber hours | rating rating
43 | 8,800| 620 x x
37 600 eo} x
41 | 11,200; 650/ x x
4g | 1,685; 79! X x
4g | 12,271 | 3,057 x
37 | 1,000] 140! x x
42 | 1,500) 105; X
50 | 6,000) 500; xX x
44 5,382 651

perience. The list was then divided into eight
levels of experience composed of five subjects
each. The subjects in each level were then ran-
domly assigned to the five groups constituting
the main study. This method was chosen to as-
sure relatively matched groups with regard to
experience and initial ability while retaining the
statistical requirement of random sampling of
the subject population. Flying experience of the
eight chosen for the control group ranged from
600 to 12,271 hours, with a mean of 5,382 hours;
ages ranged from 87 to 50 years, with a mean of
44 years. Six had commercial pilot ratings and
the remaining two had airline transport ratings.
Five possessed flight instructor ratings. None
had flown more than 10 hours instrument (sim-
ulated or actual) in the last 90 days; three had
not flown at all during that period of time.

ILS Facilities

Two instrument landing approach (ILS) fa-
cilities were used for the study; one, serving run-
way 351 at Will Rogers World Airport, Okla-
homa City, Oklahoma, was utilized when the
wind was from the north; the other, a training
facility serving runway 17 at the Chickasha,
Oklahoma airport, was used when the wind was
from the south. Approximate angle of both
glide slope centerlines was 2-14°.



pletely eliminated. This decrease in anxiety, and
the resulting stress reduction, is brought about
as the subject gains additional familiarity with
the aircraft and the characteristics of the task,
his real or fancied dangers fail to materialize as
physical consequences, and he gains confidence in
his ability to deal with an increasingly predict-
able environment. It should be nated that the re-
ported heart rates, and rates of magnitude of
change, are at all times well below those ehar-
acterized by fright or fear as found during such
stress-inducing activities as free-fall parachut-
ing2® The reported values may be more acct-
rately compared to a mild anxiety or apprehen-
sion level when related to the in-flight baseline
rate. Unfortunately, consideration dictated by
limited data recording capacity precluded the
gathering of data during the “go-around” por-
tion of each circuit. Such data might have
yielded some interesting insight on the heart rate
changes resulting from the anticipation of ini-
tiating each subsequent approach. While the de-
crease in mean overall heart rate over the 10
approaches suggests a decline in apprehension as
the subjects adapted to the total task, the lack of
reduction in magnitude of the heart rate increase
during each approach suggests an additional con-
tributing factor. This factor is probably the
stress resulting from the increase in task load as
the middle marker is approached. To under-
stand this increase requires an explanation of
the pilot’s task.

The difficulty of the task used in this study
can be described in terms of the amounts and
rates of information that must be obtained from
the flight instruments, interpreted, and translated
into psychomotor inputs to the aireraft’s controls.
In the present investigation, task performance
was related primarily to maintaining the aircraft
on the centerline of the localizer and glide slope
while keeping the heading, rate of descent, and
approach speed within specified limits.

Though all primary flight instruments play an
important role in the performance of this task,
the glide slope/localizer (cross-pointer) indicator
is, by definition of the task, the primary “fore-
ing” reference. That is, the aircraft position in
space is referenced to the cues obtained from the
cross-pointer indicator which, in effect, provides
a foreing function on the pilot to fly his plane so
as to meet the demands of the instrument.

Effective use of this instrument requires a basic
understanding of its cueing characteristics. The
horizontal (glide slope) needle moves vertically
in reference to the bull’s-eye (or “doughnut”)
and to a series of “dots” spaced in a vertical line
above and below the center of the instrument.
The span of the bull’s-eye is equal to a subtended
angle of approximately 0.28° with reference to
the vertex of the angle at the point of intended
touchdown. The vertical distance between dots,
and between the periphery of the bull’s-eye and
its center, is equal to a subtended angle of 0.14°.
Since the distance between the top and bottom
radii comprising this angle diminishes as the ver-
tex is approached (Figure 9), it is obvious that
the vertical distance equivalent to a “one-dot” dis-
lacement is a function of the distance between
the aircraft and the vertex of the angle. To find
this distance, in feet, at any point along the ap-
proach path, the following equation may be used
for approximation purposes :

S=S,, (.0025), where
S=vertical distance in feet, and
S,= distance in feet between ground-based
glide slope antenna and aircraft, and

.0025=factor for one dot of glide slope needle
displacement.

For example, the maximum vertical envelope
within which the aircraft must remain to keep
the glide slope needle within the confines of the
bull’s-eye (2 dots) is about 100 feet at a point
slightly less than 4 miles (20,000 feet) from the
glide slope transmitter antenna, while at a point
2,000 feet from the antenna the same bull’s-eye
envelope comprises only 10 feet. From this, it
can be seen that the task of keeping the glide
slope needle within the center of the bull’s-eye
is equivalent to flying the aircraft from the base
toward the apex of a narrow isosceles triangle.
Thus, the human performance requirements in-
herent in this tracking task will vary in degree,
depending upon (a) the location of the aircraft
(b) the response characteristics of the total air-
craft and instrument system; and (c) the ve-
locity of the aircraft.

Tt follows that for a given vertical displace-
ment of the aircraft at a given forward velocity,
the distance and rate of movement of the glide
slope needle across the face of the instrument
will increase as the aircraft moves toward the
middle marker. This means the pilot is faced not


IIL. Results. zones and between the fourth and fifth time zones
(see Figure 6) have been shortened by a few
seconds to facilitate data handling, but this
minor accomodation is not considered to have a
points on each curve represent the mean heart significant influence on the data or the validity of

rates derived from five 15-second time periods the analysis reported below.
spaced along the approach path to the middle Mean heart rate changes within approaches
marker as illustrated in Figure 6. The relative remained relatively constant throughout all ap-

time intervals between the first and second time _ proaches, ranging from 3.6 to 6.0 beats per min-
ute (BPM). For eight of the 10 approaches, the

108 increase was between 5.0 and 6.0 BPM. The mean
increase for all 80 approaches was 5.2 BPM. Fig-
ure 7 illustrates the typical pattern of mean

t00 7 sone wanes heart rate increase found in this study. Curve
) “A” traces the actual calculated data points for

The mean heart rates for the eight subjects
during the 10 consecutive simulated instrument
approaches are presented in Figure 5. The data

ow the combined data for all approaches while curve
“B” is a straight line approximation that best

uu
» 7 7 a fits the plotted data points. The values are
v plotted with reference to an in-flight mean “base-
sol. AY line” heart rate of 88.8 BPM established approx-
imately 15 minutes prior to the first approach

“#9 M0

MEAN HEART RATE - BPM

while the subject flew the aircraft in level atti-

tude. The use of this mean reference value is

“2 #3 ee Se aT merely a convenience and is not meant to imply

APPROACHES a representative relationship between the base--

Ficure 5, Heart rate means of eight pilots flying ten _ine value and the heart rate increases during any

simulated instrument approaches. The points on each given trial, since the mean overall heart rates (to
curve represent (from left to right) the mean rates for . .

which the heart rate increases are referenced) de-

five 15-second time zones spaced along the approach . .
p..th to the middle marker. cline on successive approaches.

HEART RATE - 6PM

"OUTER MARKER"

15 SEC. 1S SEC. 1S SEC. 1S SEC. \5_ SEC.
ZONE ZONE ZONE ZONE ZONE

Ficure 6. Heart rate data was collected continuously between outer and middle markers during approaches. Data
sused in this study was taken from five 15-second time zones spaced progressively to the middle marker.

5



Experimental Procedure

Prior to flight, three disposable electrodes were
taped to the subject’s chest at the sternum and
checked in the laboratory to confirm proper func-
tioning. The subject was then briefed on the
manner in which the flight would be conducted.
The subject was given a headset to wear during
flight so as to exclude all radio communication
and to minimize extraneous cockpit noise, while
permitting the safety pilot to communicate with
the subject via the interphone.

The aircraft was started, taxied to the active
runway and “run-up” by the safety pilot. The
“slats” were then installed in front of the sub-
ject, effectively blocking his view of the outside
world. The take-off and initial climb-out were
made by the safety pilot. About 1-4 minutes
after take-off, with trim set for “cruise-climb”,
control of the aircraft was given to the subject
with instructions to climb to, and maintain, a
specified altitude. At the specified altitude, the
subject was told to execute a series of left and
right turns using bank angles of 10°, 20°, and
30°, respectively. Following these maneuvers,
the landing gear was extended and the flaps,
power, and RPM were set. in the landing approach
configuration by the safety pilot. The subject
then practiced a partial-power descent to ap-
proach altitude, varying power as required to
maintain a specified rate of descent.

Regardless of the subjects’ degree of familiarity
with the aircraft, total in-flight indoctrination

Middle Marker, (center line of ge sope
‘approximately 200 feet above terrain
‘ar this polar

time for each subject was approximately 20 min-
utes, and involved identical maneuvers. Limiting
this familiarization period to an “under-the-hood”
environment was considered to be effective in
minimizing performance variability due to the
subjects’ varying degrees of experience with the
size, type, and specific aircraft used for the study.

Ten straight-in ILS landing approaches were
then performed at approximate 10-minute in-
tervals (Figure 4). Prior to each approach, the
safety pilot placed the aircraft on the centerline
of the glide slope/localizer “beam” at a fixed
geographical point. Speed, power, gear, and
flaps were set in “approach configuration” before
turning control of the aircraft over to the sub-
ject. In this way, all subjects started their ap-
proaches in identical approach geometry from
the same point in space, without the responsibility
for navigating to that point. Upon completion
of each approach at the middle marker, the safety
pilot raised the landing gear and flaps, instruct-
ing the subject to “go around.” All air traffic
control conversations were excluded from the
subject’s headset during the approaches. Also,
jn order to further eliminate any uncontrolled
variables which might adversely affect the intent
of the main study, the subjects’ primary attention
was devoted to flying the aircraft; their attention
was not diverted to other tasks such as chart
yveading or checking engine gauges, etc.

Gsographice! Fix (teoreice! outer marker).
Glide slope centerine approsimorely 1460 teer
above ground or ths pont. X\

RUNWAY

5.5 MLES

SSS SS SS SSS

\ 0 “womese
\ : \
»~
NX

~— —— 4 —

DATA COLLECTION AREA.

\Sefery Pier takes control ond turns
aireratt inbound to lcalizer / glide ~
ope while soft reste fr one minute. \

a

Figure 4. Flight path used for study of pilot performance during simulated instrument approaches.

After go-around, the subject climbed back to
initial approach altitude; he was then given a
1-minute rest period while the safety pilot made
a 180° turn inbound to the glide slope/localizer

centerline, where the procedure was repeated.
The flight was terminated after the 10th ap-
proach, with the safety pilot landing the air-
craft.


proach #1 and approach #10. Two of the three
showed a mean increase of 0.2 and 0.8 BPM and
the third a mean decrease of 2.0 BPM. The two
largest individual decreases (24.0 and 26.2 BPM)
coincide with the two subjects having the highest
mean heart rates during approach #1. No fur-
ther attempt has been made to compare heart rate
level, heart rate changes, in-flight baseline rates,
flying experience, or age of subjects for the pur-
poses of this part of the overall study. Curves
“A” and “C” in Figure 8 are included for com-
parison only. They are the mean heart rate levels
at the middle and outer marker respectively, and
correspond to the last and first points of the
curves in Figure 5. Curve “B” includes the
values of Curves “A” and “OC”. All three curves
have approximately the same shape except that
the values for Curve “A” tend to be less con-
sistent than the others.

105
104

BEATS PER MINUTE
Sssexesesges gs

eas

'2 3 4 5 6 7 8 9 10

APPROACHES
Ficure 8. Mean heart rate levels during each approach.

The analysis of variance reported in Table IT
shows the overall differences in heart rate levels
between approaches to be significant (p= <.001).
Both the linear (p=<.001) and the quadratic
(p= <.01) components are significant. No at-
tempt was made to partition the sequence of ap-
proaches to attribute a singular component to a
particular segment of the function. Similarly,
no subsequent tests of significance were performed

on any pair combinations or to determine if the
curve had reached an asymptotic value.

IV. Discussion.

Two distinct and statistically significant heart
rate patterns were exhibited by the subjects under
the conditions of the experiment reported here.
One was the long-term decrease in mean overall
heart rate across successive approaches, and the
other was the consistent increase in mean heart
rates during each approach.

When endeavoring to equate changes in heart
rate levels with changes in stress levels, it must
be recognized that any apparent stress may be
the result, not of a single type of stress, but
rather of the complex interaction of a number
of psychological and physiological factors op-
erating concurrently.’ However, the main sources
of stress assumed to be responsible for the heart
rate changes found in this study can be roughly
divided into two major categories: (a) The sub-
jective elements introduced by the individuals and
(b) those related to the objective difficulty of the
task.

It seems reasonable to assume that the’ long-
term decrease in overall mean heart rate can be
equated to the classical accommodation (habitua-
tion) effect. This assumption is supported, in
part, by the fact that the observed values are in
excess of, but declining toward, the mean in-
flight baseline heart rate. This indicates that the
elevated mean heart rates, especially those for
the initial approaches, are indicative of a degree
of stress to which the specific short-term task
performance stressors are only a contributing
factor. The source of this stress may be at-
tributed largely to the highly subjective percep-
tions and expectations the individual brings to
the total flying task. These may include, but are
not limited to, his evaluation of fancied or real
dangers in the situation’, his inherent and learned
coping mechanisms for dealing with a particular
type of stress*, his understanding of the instruc-
tions given him and the explanation of the pur-
pose of the task’, his fear of failure—independent
of the physical consequences of such failure®, and
his sense of responsibility while having control
of the aircraft.

As successive approaches are completed, these
sources of stress may be assumed to decrease in
significance, though they probably are never com-



AM 70-7

PILOT HEART RATE DURING IN-FLIGHT SIMULATED
INSTRUMENT APPROACHES IN A GENERAL
AVIATION AIRCRAFT

A. Howard Hasbrook
Paul G. Rasmussen

Approved by Released by

Dhl Rte PU Siegel sd

J. Rosert Diniz, M.D. P. V. Sreczn, M.D.
Cuter, Crvm ArromepicaL Fevmrat Arr Surcron
InsrrruTe
April 1970

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



mally considered to be highly stress in-
ducing, such as free-fall parachuting.

7. Heart rate changes during approaches ap-
pear to be related to the pacing stress in-
duced by specific characteristics of the
man-machine interface.

Even a cursory survey of the human factors
research literature indicates that relatively little
is known about the effect. of stress on total pilot
performance. Though there are many potential
sources of stress that may be operating at any
given time during a flying mission, the stress
resulting from inadequately designed man-ma-

chine system interfaces is probably the most. per-
vasive, consistent, predictable, and amenable to
modification. Fox et al.2, have presented a very
succinct statement of the type and extent of re-
search effort required to gain the information
necessary for an understanding of the airplane-
pilot system. As part of such a research pro-
gram, it is suggested that a major effort be di-
rected toward identifying and evaluating the
sources of human stress in the airplane-pilot sys-
tem interface under the widest possible range of
flight conditions. On the basis of information
gathered in this area, it should be possible to de-
sign safer and more efficient systems.

REFERENCES

1, Bjurstedt, H. and Mattell, G., “Cardiovascular and
Respiratory Reactions in Mental Stress.” In 1. Levi
(Ed.) Emotional Stress, Proceedings of an Interna-
tional Symposium. Forsvarsmedicin, Vol. 3, Suppl.
2, Stockholm, 1967.

. Fox, J. G., Ferguson I., and Andrew, I. D. C., “An
Annotated Bibliography of Presentation of Informa-
tion in Aircraft Cockpits.” S & T Memo 3/66, p.
77-78. Technical Information and Library Services,
Ministry of Aviation, May 1966. (Available as AD
634575).

. Frankenhauser, M., “Some Aspects of Research in

Physiological Psychology.” In L. Levi (Ed.) Emo-

tional Stress. Proceedings of an International Sym-

posium., Forsvarsmedicin, Vol. 38, Suppl. 2, Stock-

holm, 1967.

Harris, W., Mackie, P. R., and Wilson, C. L. Research

on the Development of Performance Criteria, Tech-

nical Report VI: “Performance Under Stress.”

Washington, Department of Navy, July 1956,

Lager, C. G., “Experimental Methods and Results
of ‘Stress’ Measurements in Simulated Flight.” In

s

a

10

L. Levi (Ed.) Emotional Stress. Proceedings of an
International Symposium. Forsvarmedicin, Vol. 3,
Suppl. 2, Stockholm, 1967.

. Lazarus, R. S. “Stress Theory and Psychophysi-

ological Research.” In L. Levi (Ed.) Emotional

Stress. Proceedings of an International Symposium.

Forsvarsmedicin, Vol. 8, Suppl. 2, Stockholm, 1967.

Levi, L., “Some Principles and Sources of Error in

Psychophysiological Research.” In L. Levi (Id)

Emotional Stress, Proceedings of an International

Symposium. Forsvarsmedicin, Vol. 3, Suppl. 2,

Stockholm, 1967.

. Melton, C. B., Wicks, M., Saldivar Jr., J. 'T., Morgan,
J., and Vance, F. P., “Physiological Studies on Air
‘Tanker Pilots Flying Forest Fire Retardant Mis-
sions.”. OAM Report AM 68-26, 1968.

. Roman, J., “Risk and Responsibility as Factors Af-

fecting Heart Rate in Pilots.” The Flight Research

Program—II. Aerospace Med. 86: 518-528, 1965.

Schane, W. P. and Slinde, K. E., “Continuous EKG

Recording During Free-Fall Parachuting.” USAARU

Report No. 67-7, 1967.

10.


Sinpltied Che Sipe Dior
“BULLS-EYE" —inentar sos anfeoae
+2 dors 0) seston!

+ 0.28°

Ficure 9, Two-dot deviation (equal to vertical displace-
ment of glide slope needle across span of bull’s-eye on
center of indicator) is equal to about 0.28° of sub-
tended angle. This results in various “beam depths”
depending on distance of aircraft from runway.

only with the necessity of increasing the speed
of his cognitive, intellectual, and reactive proc-
esses, but he must also cope with a constantly
changing control-display ratio that requires di-
minishing amplitudes of control input to achieve
a given degree of corrective action as reflected on
the cross-pointer instrument. These conditions
impose a speed or pacing stress, at an increasing
rate, which may sooner or later seriously impair
the quality of his performance of the task.

In the present study, the effect of the pacing
stress cannot be definitely separated from any
stress which might be associated with anxiety
related to the aircraft’s decreasing altitude during
the approach. There is some suggestion that
flight near the ground—as at the middle marker—
as well as critical and demanding maneuvers,
tend to add to the pacing stress. It should be
pointed out that these increases have little, if any,
clinical significance and may even be beneficial
from an “alerting” point of view. Roman® found
that experienced military pilots flying high-per-
formance aircraft exhibited higher heart rate
levels than did their “passengers” (who were
equally experienced pilots) during low-level “con-
tact” (VFR) flights near the ground. These
differences in stress levels were more pronounced
for the more demanding or critical portions of
the flights. This suggests that stress induced by
performance demands may be more significant
than the stress introduced by normally encoun-
tered risk-induced anxiety.

Overall mean heart rates and mean heart rate
increases are, of course, influenced by a great
many factors. The magnitudes of both measures

reported in this study may be less than those
that can be expected to be encountered in actual
IFR/ILS approaches due to the modified work-
load in this study, and because of the security
provided by the safety pilot who had visual con-
tact with the outside world at all times. The
variability of individual heart rate patterns
during approaches may be attributed to the sub-
jects’ own perceptions of the quality of their
performance at any given moment and may, or
may not, coincide with the objective measures.
Individual short-term reactions to incidental
events in the environment, such as unexpected
turbulence or increased activity of the safety pilot
attempting to maintain visual contact with other
traffic, may also significantly influence the results
for a given subject on a given approach. Finally,
the element or characteristic of the approaches
that almost consistently coincided with the
highest mean heart rate increase was the onset of
over-control of the aircraft by the pilot, as in-
dicated by rapid and extensive oscillations of
the glide slope needle. This over-control may be
attributable to the pilot’s lack of ability to adapt
adequately to the changing control-display re-
lationship.

V. Summary and Conclusions,

Heart rate data were recorded on eight com-
mercial or ATR instrument rated pilots during
a total of 80 simulated in-flight instrument ap-
proaches. Analysis of the data indicated that:

1. Mean heart rate changes were relatively
constant throughout all approaches.

2, Mean heart rate increases ranged from 3.6
to 6.0 BPM for the 10 approaches of each
flight, with a mean increase of 5.2 BPM
for all 80 approaches.

3. Individual heart rate changes between the
outer and middle markers ranged from a
decrease of 6 BPM to an increase of 15
BPM.

4. Individual maximum variations within ap-
proaches ranged from 1 BPM to 16 BPM
and averaged 7.9 BPM for all 80 ap-
proaches.

5, Overall mean heart rate declined 11.0
BPM across the 10 approaches.

6, All heart rate levels were well below those
generally associated with activities nor-



An analysis of variance was performed on the
data and the results are presented in Table II.
The increase in mean heart rate across time zones
during the approaches was highly significant
(p=<.001). The absence of a significant inter-
action between heart rate changes during ap-
proaches and the number of approaches flown
permits the combining of heart rate change data
for all approaches. Though the combined data,
as illustrated by curve “A” in Figure 7, deviate
somewhat from the straight line approximation
of curve “B”, the analysis indicates that only the
linear component of the data is significant
(p= <.001).

Tapue II.—Summary analysis of variance on heart rate
data during successive instrument approaches

Source df MS F
Approaches (A)_---_- 9 479.48 7. 79*
Linear_. 1 | 3,656.12 59. 38*
Quadratic. 1 505.05 8. 20**
Other. ._ 7 22.03 <1
‘Time Zones (B) 4 386. 61 20, 28*
ii 1 | 1,485.13 77. 91*
1 52.29 2.74
2 4,52 <1
7
36 6.67 <i
63 61.57 <1
28 19. 06 <1
252 7.43 <i
Total_....---- 399
*p —.001
**p—, 01

The significance level for the mean heart rate
changes during approaches was achieved in the
presence of considerable variation in the direction
and magnitude of individual changes, not only
from subject to subject, but also from one ap-
proach to the next for the same subject. Exam-
ination of the data showed that some subjects, on
some trials, had a lower heart rate at the middle
marker than at the outer marker, and there were
frequent instances of highest rates occurring at
intermediate points.

The largest individual, increase in heart rate
between the outer and middle marker was 15 BPM
compared to the largest single decrease of 6
BPM. One subject with approximately 1,500
hours of flying experience had a maximum heart

HEART RATE INCREASE — BPM
Ey

2
° + + + + +
w w
be os vy oF 8
go 2 @ o2 &
£2o oF 2a OF 33
= ©
wo e2¢ © eo: 2
= 6

Fieure 7. Heart rate changes during in-flight simu-
lated instrument approaches as a function of time and
distance along the approach.

rate variation of only 5 BPM, not only within
a single approach but throughout all 10 ap-
proaches. During six of the approaches, his
maximum variation was 2 BPM or less.

Because the maximum range of heart rate
change frequently did not coincide with the heart.
rate values at the outer and middle markers, the
difference between the highest and lowest rate for
each subject within each approach was deter-
mined. The smallest maximum variation within
any approach was 1 BPM and the highest was
16 BPM. The means of maximum variations
within individual approaches ranged from a high
of 9.4 BPM to a low of 6.9 BPM. The mean of
the maximum variations for all subjects on all
approaches was 7.9 BPM, as compared to the
mean increase of 5.2 BPM between the outer and
middle marker. Except for the larger magnitude
of the maximum variations, they did not appear
to differ from the values based on the outer and
midle marker with regard to their distribution
across approaches. This conclusion was not tested
statistically due to the apparent high correlation
between the two measures.

Mean heart rate levels during each approach
are presented in Figure 8. Curve “B” is based on
the average of the five data points of each ap-
proach as presented in Figure 5. The mean heart
rate level declined a total of 11.0 BPM through-
out the 10 approaches. As with ‘heart rate
changes during approaches, individual subjects
yaried considerably. Three subjects showed prac-
tically no change in mean heart rate between ap-


The instrument panel display was representative
of many such installations, consisting of a “T”
configuration (Figure 2), except for the location
of the vertical speed indicator. It was moved to
the right (Arrow #1) from under the altimeter
to provide a more centrally located space for the
glide slope/localizer indicator (Arrow #2).
Quick-removal “slats” (Arrow +3) installed
in the windshield area and to the left of the pilot-
subject effectively simulated an instrument en-
vironment without interfering with the safety
pilot’s outside vision. The slats also eliminated

Fieure 2.

2

the distracting weight and discomfort inherent
in most hood devices normally worn on the head
to simulate instrument flight.

A portable, battery-powered, seven-channel
Lockheed (Model 417) tape recorder located be-
hind the pilot’s seat (Figure 3) recorded all in-
flight data. Its operation was monitored con-
tinuously by a research engineer seated on the
right side of the plane behind the safety pilot.
The recorded data was later transferred to a
paper chart record in the laboratory by use of a
Grass recorder.

ae

Instrument panel display in research aircraft.


PILOT HEART RATE DURING IN-FLIGHT SIMULATED INSTRUMENT
APPROACHES IN A GENERAL AVIATION AIRCRAFT

I. Introduction.

Making an ILS approach through low clouds
extending to within a few hundred feet of the
ground is probably one of the most difficult-—
but routine—flying tasks facing the instrument
vated pilot. The task of maneuvering a relatively
high-speed vehicle within a constantly narrowing
electronic “beam” requires rapid acquisition and
evaluation of information provided by numerous
instruments on the cockpit panel, frequent and
often critical split-second decisions, and contin-
uous application of control inputs. These task
elements must be performed with reference to
such variables as the aerodynamic response char-
acteristics of the aircraft, information rates of
the displays, and the display-control ratio which,
in the case of the primary tracking display, is a
constantly changing relationship.

The difficulties inherent in such a complex
tracking task are frequently heightened by equip-
ment and system designs that exhibit little con-
sideration of the optimum response and operating
characteristics of the human operator? Other
factors which may contribute to the difficulty of
the task, depending on individual circumstances,
are the individual’s subjective perceptions of the
task, inadequate training and/or minimal pro-
ficiency, fatigue, chart reading, and radio com-
munications.

Eyen this brief description of the total task
implies the presence of a number of potential
sources of stress inherent in making an ILS ap-
proach. If we follow the classification of mental
stresses defined by Harris e¢ a/.*, we find that the
separate stress-inducing characteristics of the
total flying task assumed to be operating at any
given time fall almost entirely into one or more
of five categories of short-term stress. These are
fear of failure, distraction, fear of harm, physical
discomfort, and pacing or speed. Of these, phys-
ical discomfort stresses are probably the least sig-
nificant in the present context. Although all the

other categories would seem to be applicable in
varying degree, pacing or speed stress seems par-
ticularly significant in that it can be directly
identified with a quantifiable performance re-
quirement of the flying task.

This report is based on heart rate data collected
on subjects who acted as a control group for the
study of pilot response to the use of aural glide
slope cues during in-flight simulated ILS ap-
proaches in a light, general aviation aircraft. A
number of significant limitations in the use of a
single measure (such as heart rate) as a compre-
hensive stress indicator have been documented.*
However, changes in heart rate can be particu-
larly indicative of short-term changes in stress* "°,
and can be recorded without interfering with task
performance.

II. Equipment and Methodology.
Research Device

A four-place single-engine general aviation
type airplane (Figure 1) was used for the study.

Ficure 1.
formance during simulated instrument approaches was
typical of small, general aviation planes.

Aircraft used for in-flight study of pilot per-



ACKNOWLEDGMENT

Space does not permit naming all the individuals and groups who con-
tributed to the: successful completion of this study; however, we would be
remiss if we did not mention the “above and beyond” efforts of the FAA
Oklahoma RAPCON/Tower personnel who so successfully and safely inte-
grated hundreds of our simulated ILS approaches with other general aviation
and air carrier traffic. To these and all the others who helped—our thanks.

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. The general public may purchase from Clearinghouse for Federal Scientific and
Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151