e

i

3 Anonymous:

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a

10.

. Anonymous:

REFERENCES

Anonymous: Attitude Indicator Attitudes. Preven-
tion Branch, U.S. Army, Ft. Rucker, Ga., August
1968,

. Anonymous: Integrated Flight Instrumentation
Study. Project #16-56-0031, (AD 160-177) Page
87, U.S. Army Electronic Proving Ground, Ft. Hua-

chuea, Ariz., March 1958.

Integrated Instrumentation for Air-

craft. Dunlap and Associates, Inc., December 1954.

} Anonymous: Pilot Performance with Two Different

Attitude Displays. Dunlap and Associates, Ine.
(Office of Naval Research Contract NONE 1076(00),
July 19%

Equipment Used in Experiments to
Solve the Problem of Fog Flying. The Daniel
Guggenheim Fund for the Promotion of Aeronautics,
Ine., March 1930 (Cornell Univ. Library).

. Bonnell, C. R.: Outside Looking in Attitude Gyros.

Society of Automotive Engineering, Report #690326,
March 1969.

. Brown, R, C. Figure and Ground in a Two-Dimen-

sional Display. FPRC 781, University of Durham,
England, July 1952.

. Doolittle, J. H.: Early Blind Flying. Third Lester

Gardner Lecture, MI'T, April 1961.

. Fitts, P. M. and Jones, R. E.: Psychological Aspects

of Instrument Displays. I; Analysis of 270 “Pilot
Error” Experiences in Iteading and Interpreting
Aircraft Instruments. Acro, Medical Lab., Engi-
neering Division, Air Materiel Command, Dayton,

Ohio. Rep, No. RSEAA-694-12A.
Fogel, Lawrence J., A New Concept, the Kinalog
Display System. JOURNAL OF THE HUMAN

FACTORS SOCIETY, pp. 30-37, April 1959,

16

11, Gardner, John F.: Speed and Accuracy of Response
to Five Different Attitude Indicators. WADC TR
54-236, Wright Air Development Center, December
1954.

12, Gardner, John F., et al.: In-Flight Comparison of
Pilot Performance on a Standard USAF and an
Experimental Instrument Panel. NADC TR 57-270,
Wright Air Development Center, September 1957.

13. Johnson, Steven L. and Stanley N. Roscoe: What
Moves, the Airplane or the World? T. R. ONR-
70-1. University of Illinois, June 1970.

14. Kirk, Roger E,: Experimental Design: Procedures
for the Behavioral Sciences. Brooks/Cole Publishing
Company Belmont, California 1968.

5, Kitahara, Masaaki and Uno, Ryoji: Equilibrium
and Vertigo in a Tilting Environment, ANNALS
OF OTOLOGY, RHINOLOGY AND LARYNOLOGY,
76:166-178, March 1967.

16, Marks, D. A. and D, GC, Gronow: A Comparison

of the Appreciation of Aircraft Attitude Given by

Four Types of Non-toppling Attitude Indicator.

FPRC #833, RAF Institute of Aviation Medicine,

May 1953.

7. Poppen, J. Re: Equilibratory Functions in
ment Flying. JOURNAL OF AVIATION
CINE, 6:148-160, 1936.

18, Rolfe, J. M.: The Evaluation of Visual Displays
Techniques and Trends. IAM Scientific Memoran-
dum #74, RAF Institute of Aviation Medicine,
Farnsborough, Hants, England, April 1966.

Instru-
MEDI-

=

. Skelton, Gerald E.: Evaluation of a Pictorial Turn
and Bank Indicator. Report #NA-68-28, NAFEC,
FAA, August 1968.


indicator than with the moving horizon indi-
cator, F (1, 30) =22.23, p<.001. On the other
hand, there were no significant differences be-
tween the two groups when the moving-aircraft
indicator was used, or between the two types of
attitude indicators when used by the high ex-
perience group. The interaction is shown in
Fig. 8.

to)
1

g

wf /

© BF \

Ww O7

gt 7

r la

g al / oo!

z |

oO

xz 4F

ef

a

O2PF

8 ——— HIGH EXPERIENCE GROUP

Q Z —< LOW EXPERIENCE GROUP

WwW (o} 1 i

MOVING MOVING

AIRCRAFT HORIZON
INDICATOR INDICATOR

Fieure 8. Mean range of excess pitch change during
recovery to level flight (confidence levels of significant
differences are indicated where applicable).

The results for rate of pitch correction are
summarized in Table 6.

ATTITUDE INDICATOR
Pilot
Experience Moving Aircraft Moving Horizon
Full Panel | Port Panel Full Panel | Part Panel
High .80 178 .85 76
Low 49 .70 44 43

TapLe 6. Mean rates of pitch correction
during bank angle recoveries.

(deg/sec)

The relatively small values in Table 6 are
attributed to the fact that the initial pitch angles

10

were relatively small, averaging between 3° and
4°,

An analysis of variance indicated that only
the difference between pilot experience groups
was significant, F (1, 30) =12.59, p<.001.

Bank Angle Control During Alternating
Turns, Attempts to quantify bank angle contro]
during alternating turns on the basis of accuracy
and consistency of performance were unsuccess-
ful because performance by both pilot experience
groups using either attitude indicator was toc
inconsistent to provide meaningful data.

Pitch Control During Alternating Turns. The
criterion used to evaluate performance was the
ability of the subjects to maintain zero pitch
attitude. The means of the total ranges of pitch
during the maneuver are presented in Table 7.

ATTITUDE INDICATOR
Pilot
Experience Moving Aircraft Moving Horizon
High 12.13 1.00
Low 20.13 34.69

Tante 7, Mean rates of ranges of pitch changes (de-
grees during alternating turns).

An analysis of variance indicated that there
was a significant interaction between pilot ex-
perience and type of attitude indicator used
F (1, 30) =6.63, p<.05. A simple effects test
showed that the low experience group made sig-
nificantly larger changes than the high experi-
ence group when the moving-horizon indicator
was used, F (1, 60) =32.25, p<.001. The low
experience group made significantly smaller
pitch changes when using the moving-aircraft
indicator than when using the moving-horizon
indicator, F (1, 30)=1143, p<.005. The inter-
action is shown in Fig. 9.

Bank Control in Descending Turns. The ob-
jective of this maneuver was to maintain a 45°
angle of bank in a series of descending turns.
Each turn was terminated at the command of
the safety pilot after the aircraft had descended
at least a thousand feet. The percent of time
the aircraft was held in a 45° bank (=5°) is
presented in Table 8.

An analysis of variance indicated there were
no significant differences between any of the
values in Table 8,




IN-FLIGHT PERFORMANCE OF CIVILIAN PILOTS USING
MOVING-AIRCRAFT AND MOVING-HORIZON
ATTITUDE INDICATORS

I. Introduction

The first practical artificial horizon instru-
ment—or attitude indicator, as it is called to-
day—was developed in 1928 by Elmer Sperry,
Jr. and was successfully test flown a year later
in “blind flight” conditions in a U.S. Navy train-
ing plane by a Lt. James H. Doolittle of the
U.S. Army Air Corps. Based on an early con-
cept that a pilot's primary frame of reference is
his aircraft and that the earth and horizon move
in relation to the pilot and his airplane, Lt. Doo-
little specified that the instrument have a
moving-horizon bar. A small gyroscope kept the
bar (A, Fig. 1) parallel with the true horizon,

‘a’ Moving
Horizon Bar

‘B' Fixed
Aircraft Symbol

Ficcre 1. Artist's drawing of 1928 Doolittle-Sperry
artificial horizon instrument. It was similar in  ap-
pearance to contemporary attitude indicators except
for the lack of ky pointer” and bank angle indices.

regardless of normal banking and pitching mo-

tions of the aircraft. A. fixed-aireraft symbol

(B, Fig. 1) provided a means of relating the

roll and pitch attitude of the aircraft to the

horizon.

Although the basic design and operation of
the “moving-horizon” type attitude indicator
instrument has not changed in the intervening

43 years (1929-1972), there have been many re-
searchers and pilots who have questoned the
“human factors correctness” of using a moving
horizon bar rather than a moving-airplane sym-
bol in this all-important blind flight instrument.

There seems little doubt that the moving-
horizon concept leaves much to be desired.
Johnson and Roscoe (1970) showed, for example,
that of the 89 plane crashes in 1968 classified as
weather disorientation accidents, a substantial
number occurred when an airplane with a nor-
mally operating gyro horizon display (moving-
horizon instrument) was flown into the ground
in a tight spiral. Fitts and Jones (1947), in
their study of 270 errors made by pilots reading
and interpreting instruments during instrument
flight, showed that the artificial horizon (moving-
horizon) instrument contributed to a number of
reversal errors (turning or recovering in the
wrong direction) and to errors due to illusions;
seven percent of the errors involved interpreta-
tion of bank angle; another five percent was due
to misconceptions of aircraft attitude because of
conflicts between body sensations and instrument
indications. Fitts and Jones also pointed out
that “although this number [of reversal errors]
is relatively small, the consequences of these er-
rors are often tragic, and the amount of over-
learning associated with the use of this display
({moving-horizon instrument] should be closer to
zero.” (Emphasis ours.) In the past 37 years,
many other studies have been conducted to deter-
mine whether the moving-horizon bar or the
moving-aireraft symbol is more natural and
normal for human use. Poppen (1936) stated
that the correct form of presentation should be
an exact analog of what would be viewed through
the windscreen in contact (VFR) flight. Despite
the fact that virtually every research study re-
lating to the problem has favored the moving-



Appendix

Description of Low Time Flying Experience Subject Group

N:

Age:
Total Hours:
Recent Exp.:

Instrument Exp.:

Licenses:
Instructors:
T-34 Exp.:

16

24-53 yrs. (last birthday) Mean 40 yrs.

80-326 lus. (rounded to full hrs.) Mean hrs—178.
Zero to 113 hrs. last 12 mos. Mean 27 hrs. 5 Ss
with Jess than 10 hrs. last 12 mos, including one
with no time during that period.

Two to 20 hrs total (including simulator time)
Mean 7 hrs.

14 Private, 2 Commercial

None .

Only two Ss had any previous experience with the
T-34, One had 2 hrs.; the other 18 hrs.

Appendix

Description of High Time Flying Experience Subject Group

N:
Age:
Total Hours:

Recent Exp.:
Instrument Exp.:

Licenses :
Instructors:
'T-34 Exp.:

16

25-60 yrs. (last birthday) Mean 47 yrs.

1.300-18,000 hrs. (rounded to full hours) Mean
7,885 hrs.

50-500 hrs. last 12 mos. Mean 145 hrs. Approxi-
mately half with 100 or more hrs.

100-4,500 hrs, total (ineluding simulator time).
Four Ss had 1,000 or more hrs.

9 ATR, 7 Commercial

ll

6 had none; 10 had from 2 to 1,200 hrs.

17





pilots were “trained to hold their bodies—and
heads—straight with the aircraft, particularly
in turns.” This would cause the real horizon to
“roll” relative to the pilot (Fig. 12). However,

\_ Plane through pilots eyes.

~ /

S.

Real Horizon

s. “Roll” of horizon
~_telative to pllots
Neves.
S.

/

7
Axis through’head and body parallel
vertical axis of aircraft.

Froure 12. If pilot keeps his head “straight” with his
aircraft in normal (non-acrobatic) turning maneuvers,
real horizon will seem to “roll” or tilt, This head/
aircraft relationship—stressed in training since the
early 1920's—was primarily responsible for original
use of moving-horizon type of attitude indicator.

there is some indication that holding the head
straight with the airplane, while making shallow
or median banked turns with reference to the
real horizon, may be psychologically unnatural.
Our personal observation of head movements of
pilots during performance of such ground-

HeAo| AXIS
8.
‘

Vertical

| Movement
of

Horlzon

“Plane® thro

Real Horizon ‘apllotis

/
soy /axis

during

Ficure 13, Natural tendency of many

pilots
VFR flight is to hold head normal to the veal world
during shallow and medium banked turns, resulting

in real horizon remaining fixed horizontally. Although
climbing (A) or descending (13) turns cause horizon
to move vertically, it remains horizontal to pilot's
eyes.

14

oriented maneuvers as “eights around a pylon”

and “§-turns over a road” shows that many
pilots subconsciously keep their heads normal to
the real horizon (Fig. 13).

Interestingly, this holding the head (and
therefore the plane of the eyes) normal to the
horizon regardless of tilting of the body is also
evident among ice skaters, skiers, and motor-
cyclists when they tilt their bodies from side to
side during serpentine maneuvers. The phe-
nomenon can also be observed among many
members of the animal kingdom. In turns in
which the animal’s body is tilted to counteract
centrifugal force, the head is usually held normal
to the visual horizon; this is dramatically dem-
onstrated in Fig. 14 wherein a horse is shown

’ '
Fieure 14. Horse holds his unrestrained head in verti
eal position while leaning body to counteract centri

fugal force during turn around barrel. Author:
believe this head position (normal to horizon) pro
vides animal with maximum equilibrium, despite ef
fects of centrifugal force. (Photo courtesy 0
American Quarter Horse Association.)

rounding a barrel during a rodeo contest. It car
also be seen that the reins are completely slack
with the horse free to hold its head in a manne
which will provide maximum equilibrium.
Although few research references have beer
found relating to this particular subject, a Japa
nese study (1967) showed that people living i:


zation turns and calibration maneuvers, the sub-
ject remained “in-the-open” with the blind flight
hood in a stowed position.

The flight task which each subject performed
consisted of: 24 recoveries to level flight from
30° to 45° bank turns; eight 45° banked turns,
rolling consecutively from bank to bank; and
four 45° banked descending turns—or a total of
36 turns, A third of the first 24 turns were in a
coordinated condition when control was given
over to the subject; another third involved
“slipping” entries; and the remaining third were
in a “skidding” condition. Half of the 24 turns
involved use of full (all flight instruments)
panel conditions and half involved part (atti-
tude indicator only) panel conditions. Slipping
and skidding conditions were superimposed on
the turns by the safety pilot for a time sufficient
(more than 30 seconds) to confuse the subjects
as to the direction of turn before the subjects
took over control.

During the time the safety pilot was placing
the aircraft in the appropriate turn condition,
the subject kept his eyes closed and covered by
his left hand to preclude any inadvertent cueing
from shadows passing across his head. Also, he
kept his right hand away from the control stick.
Upon a spoken interphone command from the
safety pilot, the subject opened his eyes and took
control of the aircraft as he scanned the instru-
ment panel.

The sequence and conditions of the turns
(panel configuration, bank angle, direction of
turn and “coordination condition”) were sys-
tematically counterbalanced, A typical flight
protocol for one subject is shown below:

Flight Protocol
S# Name Date

Recovery Sequence

#1. Moving-Aireraft
Indicator (Full

#2. Moving-Horizon
Indicator (Full

Panel) Panel)

45 R SK 30 L SL
30 L SL 30 L SK
30 L SK 45 R SL
30 R CO 30 L C
45 L CO 45 R SK
45 R SL 45 RC

#8. Moving-Aircraft,
Indicator (Part

#4. Moving-Horizon
Indicator (Part

Panel) Panel)
45 L SL 45 R CO
4 L SK 30 L CO
30 R CO 30 R SL
30 R SL 45 L SL
45 L CO 30 R SK
30 R SK 45 L SK
Alternating Turns (45° Bank)
Moving-Aircraft Indicator L-R-L-R
Moving-Horizon Indicator R-L-R-L

Descending Turns (45° Bank)
Moving-Horizon Indicator Left,

Moving-Aircraft Indicator Right
Moving-Horizon Indicator Right
Moving-Aircraft Indicator Left

Rate of entry into the turns was controlled by
the safety pilot to prevent the subject from ac-
curately assessing the direction of turn and the
pitch attitude.

Ii. Results

Recovery from 30° and 45° Bank Angles. The
mean values appearing in the various tables and
figures of the text should be used only as com-
parisons rather than as absolutes. Not only were
different magnitudes of initial bank angles em-
ployed, but switching from one instrument and
panel combination to another may have intro-
duced transfer or sequence effects that could
have influenced the gross numbers used to express
performance. However, the values are compar-
able because all such effects have been system-
atically counterbalanced.

Two magnitudes of initial bank angles and
two directions of turn were employed to intro-
duce a means of minimizing anticipatory esti-
mations of required corrections by the subjects.
All initial conditions were counterbalanced and
the data combined for the purpose of statistical
analyses.

Initial Control Reversals. A subject’s control
response was scored as a reversal if the indicated
bank angle increased by two degrees or more
above the value recorded at the time he took
control of the aircraft. To avoid interpreting
minor control irregularities during transfer of
control as potential control reversals, the bank


Frrure 2. Outsiae-in (moving-aircraft) attitude indicator
moved both vertically and rotationally for pitch and bank information.

CAUTION
CAGE DIRECTIONAL
{S5YRO FOR AEROBATICS

(lett) utilized fixed-horizon and aircraft symbol that
To provide space for these move-

ments required use of a smaller aircraft symbol than that used in the contemporary inside-out (moving-hori-
zon) attitude indicator (right). Both indicators in this photo depict an attitude of approximately 48° right
bank and 10° nose down. However, the moving-horizon bar (B) can be mistaken for an aircraft symbol, giv-
ing initial impression of climbing turn to left, Pointer (C) moving toward left may also tend to psychologically

say, “We're turning left.”

identical in each indicator; (3) vertical displace-
ment of the moving aircraft symbol for a given
pitch change was twice that in the moving-
horizon instrument; and (4) sky-ground colors
on the instrument faces differed. It would, of
course, have been ideal to have had identical
appearance and pitch displacement in both in-
struments, but this could not be done within
time and financial restraints,

II. Equipment and Methodology

A Beech T-34 two-place military trainer
(Fig. 8) with tandem seating and a blind flying
hood over the rear cockpit was used in the study.
(This aircraft was particularly appropriate for
the study because its design strength—more than
8g positive and 4g negative—eliminated much
of the hazard involved in permitting the sub-
jects to lose control of the aircraft, as some did.)
A Lockheed model 417 recorder was installed in

the rear baggage compartment for the acquisi-
tion of pitch and roll data.

The test attitude indicators were installed in
the instrument panel of the rear cockpit. Each
subject was exposed to four different instrument
displays (Figs. 4a, 4b, 4c, 4d), in a statistically
designed sequence, during the recoveries from
banks to level flight. These four consisted of
two full panel displays (all flight instruments
available for use) and two part panel (attitude
indicator only) displays. In the alternating
turns and the descending turns, only the part
panel was utilized. However, the airspeed indi-
cator was added to the part panel in the descend-
ing turn maneuver. Cardboard disks with
adhesive tapes were used to cover instruments
not used during the flights. A bank and pitch
calibration unit was installed ahead of the wind-
shield (Fig, 5); this was used by the safety pilot
to calibrate the recorder and the visual indica-
tions of the rear cockpit attitude indicator in-



airplane form of presentation (Johnson and
Roscoe, 1970), the rationale favoring the moving
horizon attitude form of presentation has pre-
vailed through the years. Interestingly, most
of these studies used ground-based, fixed (or in
a relatively few cases, moving-base) trainers or
simulators, in which little or no acceleration
forces were present. The few studies which did
use actual aircraft involved high-performance
military planes in which “smooth are” tracking
tasks were performed by highly experienced
military fighter pilots and test pilots. Unfortu-
nately, these provided little indication of what
the results might be during routine IFR condi-
tions with ordinary civilian pilots. This is prob-
ably one of the major reasons why little serious
thought has been given by operational personnel
to switching over to the use of the moving-
airplane instrument. Despite the weight of re-
search evidence favoring its adoption, it seems
that many operational people still feel the va-
lidity of results from ground-based simulators
and training experiments has not been sufficiently
established for situations in which physical ac-
celeration cues are bound to be important. Per-
haps they also feel the results of the few flight
experiments conducted in the past have been too
unrealistic in task requirements to be useful in
making such a far-reaching decision, An inter-
esting exception, however, is that the USAF
Development Engineering Inspection Board for
the North American F-108 long-range inter-
ceptor unanimously decided to adopt the moy-
ing-airplane steering display for the F—108 air-
plane. Unfortunately, the F-108 program was
cancelled too soon for operational experience to
be gained on the use of this “new” display
concept.

In general, previous research, involving little
or no acceleration forces, showed that:

1. Low-time pilots and non-pilots responded
more rapidly and more often correctly to the
moving-aircraft instrument.

2. Positive transfer for all pilots and non-
pilots was greater when switching from the
moving-horizon to the moving aircraft instru-
ment.

38. All pilots and non-pilots demonstrated
fewer reversals with the moving-aircraft instru-
ment.

4. Low-time pilots and non-pilots subjectively
“felt” that the moving-airplane instrument was
more “natural” and “easier to interpret.”

5. Initially, experienced high-time pilots sub-
Jectively were more “at ease” with the moving-
horizon instrument.

Concerning these findings, however, Johnson
and Roscoe (1970) pointed out “it is essential
that certain critical experiments be conducted in-
flight to eliminate the possibility of drawing
spurious conclusions from a simulated flight en-
vironment. Both the speed of learning by rela-
tively inexperienced pilots and the ease of
transition of highly experienced and currently
proficient pilots must be measured”; they also
emphasized that “flight tasks must be opera-
tionally realistic and representatively difficult
and stressful.”

In order to examine the problem in an environ-
ment representative of several general aviation
instrument flying situations—in which accelera-
tion loads and some form of psychological flight
stress would be present—an FAA-CAMI in-flight
study was initiated. Designed to measure pilot
performance while using the moving-airplane-
symbol instrument and the moving-horizon-bar
instrument, the in-flight study—utilizing a gen-
eral aviation type aircraft—included the follow-
ing maneuvers: (1) recoveries to level flight
from shallow and steep turns; (2) performing a
series of left and right turns while maintaining
a level pitch attitude; and (3) maintaining a
given airspeed while performing a series of
spiraling descents.

Subjectively, these tasks appeared to be highly
stressful to many of the subjects and, in fact, a
few subjects lost control of the aircraft and gave
up after unintentionally getting into “graveyard”
spirals—some involving more than 5g normal
acceleration. Because of this, as well as on the
basis of the other results of this in-flight study,
it is suggested that the data in this report may
be viewed as being reasonably representative of
pilot performance in certain “real life” instru-
ment flying environments. However, these facts
should be noted: (1) the attitude indicators used
in the study were not exact duplicates in “face-
format” (the aircraft symbol in the moving-
aircraft instrument [A, Fig. 2] was smaller than
the one in the moving-horizon instrument [B,
Fig. 2]; (2) roll and pitch indices were not



buildings permanently tilted by earthquakes
tended to visually orient their heads normal to
the horizontal/vertical lines of the building's
interior. Thus, it may be speculated that man
prefers to keep his eyes normal to his visual
environment. This would mean keeping his head
normal to the real horizon during VFR flying;
but during instrument flying, he would keep his
head normal to the cockpit—and to the instru-
ments. By this reasoning, the horizon bar in the
attitude indicator should remain horizontal to
the cockpit (and to the pilot) moving only in
the vertical plane to depict pitch changes (Fig.
11). Rolling of the aircraft symbol to depict
bank angle should also be psychologically ac-
ceptable, since man is used to seeing birds, ani-
mals, and airplanes bank in relation to the real
horizon.

‘As a final note concerning this in-flight study,
it should be mentioned that the subjective por-
tion of our evaluation of the two attitude indi-

15

cators produced erroneous impressions. Although
the investigator-pilot was trained as an objective
observer, an unconscious bias apparently was
activated, causing him to believe from his in-
flight observations that the moving-aircraft in-
dicator provided overall improvement in per-
formance regardless of pilot experience. Also,
many of the subjects stated they felt their per-
formance was much better with the moving-
aircraft instrument. Statistical analyses, of
course, showed these beliefs to be erroneous in
large part. This points out the hazard of testing
and judging the relative merits of aircraft in-
struments and control systems on the basis of
subjective evaluation—as has been done some-
times in the past—even when some or all the
testers are highly trained and experienced pro-
fessional test pilots. Only by use of judicious
flight protocol design and statistical testing can
the true merits of a particular instrument or
system be disclosed.



Fievre 5.

strument, and to accurately place the aircraft in
proper attitude prior to letting the subject take
control during each test segment of the flight.
Subjects. Thirty-two male, FAA-certificated
pilots from 24 to 60 years of age (mean age,
43.5 years), were used as subjects. Nine held
ATR ratings; another nine were commercial
pilots; the remaining 14 held private pilot cer-
tificates. Only one (a commercial pilot) was
not instrument rated; he was “in-training” for
an instrument rating. Total flying time of
the subjects ranged from 80 to 18,000 hours,
with a mean of 4031 hours, They were divided
into two groups of low time and high time. The
low-time subjects had a total flight experience
of less than 400 hours with a mean of 178 hours;
the high-time subjects had more than 1000 hours,
with a mean of 7885 hours (see appendix).
Statistical Methods. The flight protocol was
designed to provide statistically valid data.
The data were tested using two methods: Anal-
ysis of Variance (type SPF-P.qr Design, Roger

In-flight view showing sighting device (A) mounted ahead of windshield and windshield lines (B) used
by safety pilot to place aircraft in proper attitude while he remained visually alert for other aircraft in area.

Kirk, pp. 299-307) and Simple Effects Test
(Roger Kirk, pp. 303-806).

Briefing. Each subject received a standard
pre-flight briefing, and was asked not to discuss
the flight with other subjects-to-be. The pre-
flight briefing consisted of informing the subject
that he would be recovering to straight and level
flight from medium and steep turns, flying a
sequence of alternating left and right turns while
attempting to maintain a level pitch attitude,
and maintaining a given airspeed during de-
scending left-hand and right-hand spirals, He
was also informed that the aircraft would never
be in an inverted attitude when control was
given to him.

The aircraft was started, taxied and taken off
by the safety pilot, with the subject in the rear
cockpit. After departing the traffic pattern, and
with the aircraft trimmed for cruise climb, con-
trol was turned over to the subject with instruc-
tions to climb to a given altitude. During this
time, as well as during the subsequent familiari-



TECHNICAL REPORT STANDARD TITLE PAGE

Report No. 2. Government Accession No. 3. Recipient’s Catalog No.
FAA-AM-73-9

Title and Subtitle 5. Report Date
IN-FLIGHT PERFORMANCE OF CIVILIAN PILOTS USING June_1973

MOVING-AIRCRAFT AND MOVING-HORIZON ATTITUDE INDICA- | 6- Performing Organization Code
TORS

Author! s) 8.

Performing Organization Report No.

A. Howard Hasbrook and Paul G, Rasmussen

Performing Organization Name and Address 0. Work Unit No.

FAA Civil Aeromedical Institute
P. 0. Box 25082
Oklahoma City, Oklahoma 73125

11. Contract or Grant No.

13. Type of Report and Period Covered

Sponsoring Agency Name and Address

Office of Aviation Medicine
Federal Aviation Administration

800 Independence Avenue, S.W.
Washington, D.C. 20591
‘Supplementary Notes

14. Sponsoring Agency Code

Work was performed under Task No. AM-A-72-PHY-50.

Abstract

The in-flight performance of civilian instrument-rated pilots using two different
types of attitude indicators in a general aviation aircraft was measured during
typical instrument flying maneuvers. The instruments were an inside-out (moving-
horizon) indicator and an outside-in (moving aircraft) indicator. The subjects
were divided into low and high experience groups. The results of the study differ
in some degree with those of some recent ground-based studies which used the same
two concepts of attitude presentation. However, one result of the in-flight study
agreed with many of the previous studies; low time pilots exhibited a narrower
range of pitch excursions with the outside-in (moving aircraft) attitude indicator
than they did with the inside-out (moving horizon) indicator. When combined with
the authors' observations of a head-horizon tilt phenomenon relating to both
humans and animals, the results of this study suggest the usefulness of a new
concept for the design of the attitude indicator display. A new concept is
described in this report.

18, Distribution Statement

Availability is unlimited. Document may
be released to the National Technical In-
formation Service, Springfield, Virginia
22151, for sale to the public.

Key Words

\eronautics; Instrument Flight; Avia-
sion Safety Flight; Human Engineering
Research; Human Displays Design

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Inclassified

20. Security Classif. (of this page)

Unclassified

21- No. of Pages

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DOT F 1700.7 (2-69)



Mean

Rate F Ratio Significance

Groups (Deg/sec) & df Level
High - Aircraft - Full 5.63 10.35 (1, 60) -005
Low - Aircraft - Full 3.71
High - Aircraft - Part 4.90 2.65 (1, 60) N.S.
Low - Aircraft - Part 3.89
High - Horizon - Full 6.16 14.72 (1, 60) .001
Low - Horizon - Full 3.76
High - Horizon - Part 6.79 22.44 (1, 60) .001
Low - Horizon - Part 3.83
Aircraft - High - Full 5.63 2.35 (1, 60) N.S
Horizon - High - Full 6.16
Aircraft - High - Part 4.90 29.08 (1, 60) 001
Horizon - High - Part 6.79
Aircraft - Low - Full 3.71 <1
Horizon - Low - Full 3.76
Aircraft - Low - Part 3.89 <i
Horizon - Low - Part 3.83
Full - High - Aircraft 5.63 7.53 (1, 60) OL
Part - High - Aircraft 4,90
Full - High - Horizon 6.06 5.74 (1, 60) 05
Part - High - Horizon 6.79
Full - Low - Aircraft 3.71 <1
Part - Low - Aircraft 3.89
Full - Low - Horizon 3.76 <1
Part - Low - Horizon 3.83

Legend: High, Low - (pilot experience)
Aircraft, Horizon - (type of attitude indicator)

Part, Full - (panel configuration)

Taste 4. Component comparisons of three-way interaction for rate of recovery from banks.


angle trace had to demonstrate a specific depar-
ture from the established value (or trend of
values where absolute consistency of bank angle
could not be attained) in order to be scored as a
reversal.

The mean number of bank angle reversals re-
corded for each sequence of six recoveries to
level flight are presented in Table 1.

ATTITUDE INDICATOR
Pilot
Experience Moving Aircraft Moving Horizon
Full Panel | Part Panel | Full Panel | Part Panel
High 0.81 1.00 0.56 0.31
Low 1.56 0.69 1.75, 1.75,

Tanre 1, Mean number of bank angle control reversals
during each sequence of six recoveries to level flight,

Analysis of variance showed a significant in-
teraction between experience level and type of
attitude indicator, F (1, 30)=6.11, p<.05. A
simple effects test of the interaction indicated
that there was a significant difference between
the two experience levels when the moving-
horizon indicator was used, F (1, 60) =97.56,
p<.001, but not when the moving-aircraft indi-
cator was used. The components of the inter-
action are graphically depicted in Figure 6.

2.0,
oa
-_—
fe)

—— HIGH EXPERIENCE GROUP
{ —— LOW EXPERIENCE GROUP
n n

MOVING MOVING
AIRCRAFT HORIZON
INDICATOR INDICATOR

MEAN NUMBER OF REVERSALS

Figure 6. Mean number of reversals for each sequence
of six recoveries to level flight (confidence level of
significant difference is indicated where applicable).

Time to Recover First 10° of Bank Angle.
This performance measure was based on the time

(in seconds, measured to the nearest quarter
second) between the moment the experimenter
relinquished control of the aircraft to the moment.
the subject had reduced the bank angle by 10°.
This elapsed time included the period involving
transfer of control, the subject’s reading and
interpreting the applicable instrument(s), and
the time used to reduce the bank angle by 10°.
Where initial control reversals were experienced,
the time expended by these control actions were
also included in the elapsed time. The mean
times to recover the first 10°-of bank angle are
presented in Table 2.

ATTITUDE INDICATOR
Pilot
Experience Moving Aircraft Moving Horizon
Full Panel | Part Pane! | Full Panel | Part Panel
High 3.06 3.28 2.61 2.55
Low 4.88 3.91 4.58 4.13
Taste 2, Mean time (in seconds) to recover first ten

degrees of bank angle.

Analysis of variance showed a significant dif-
ference between recovery times for the moving
horizon indicator (3.46 sec.) and the moving-
aircraft indicator (3.78 sec.), F (1, 30) =4.82,
p<.05. There was also a significant interaction
between pilot experience level and instrument
panel configuration (full or part), F (1, 30)=
5.63, p<.05. A simple effects test showed that
the high experience group performed significantly
faster than the low experience group on both
the full and partial panels. However, the low
experience group recovered faster with the par-
tial panel while the high experience group did
equally well with either the full or partial panel.

Rate of Recovery from Established Bank
Angles. Rate of recovery to wings-level flight is
expressed in degrees-per-second rather than as
elapsed time so as to minimize the effects of

ATTITUDE INDICATOR
Pilot
Experience Moving Aircraft Moving Horizon
Full Panel | Part Ponel | Full Panel | Part Panel
High 5.63 4.90 6.16 6.79
Low 3.71 3.89 3.76 3.83

Taste 3. Mean rates of recovery (deg/sec) to level
flight from established bank angles.



Ficure 3. Aircraft used in study was a two-place Beechcraft Mentor (T-34) whose performance and handling
characteristics are similar to contemporary, light 4-5 place general aviation aircraft; however, pitch and roll
is by use of a stick rather than by a wheel.

Fioune 4A

|
|
'

Ficure 4D

Freure 4, Each subject was exposed to four different instrument displays in a statistically designed sequence—
two utilizing the moving-horizon attitude instrument and two with the moving-aircraft instrument. Each of the
two displays was divided into full (4a and 4b) and part (4¢ and 4d) panels. As shown in 4c and 4d, the only
instrument available for aircraft attitude information was the attitude indicator. In descending turns, the
airspeed indicator was also available in the part panel display.

4






407

30

20Fr

——— HIGH EXPERIENCE GROUP
—T Low EXPERIENCE GROUP

MEAN RANGE OF PITCH CHANGES
\

MOVING MOVING
AIRCRAFT HORIZON
INDICATOR INDICATOR

TreurE 9. Mean range of pitch change during alter-
nating turns (confidence levels of significant differ-
ences are indicated where applicable).

. ATTITUDE INDICATOR
Pilot
Experience Moving Aircraft Moving Horizon
High 49.03 47.43
Low 47.07 43.63

Lante 8. Percent time pilot maintained 45° (5°) of
bank during descending turn.

Pitch Control in Descending Turns, Pitch
yontrol was examined reiative to pitch changes
nade by the subjects in their attempts to main-
‘ain the desired airspeed. Relatively large pitch
shanges were judged to indicate less satisfactory
yitech control than smaller pitch changes. ‘The
pitch range means are presented in Table 9.

ATTITUDE INDICATOR
Pilot
Experience Moving Aircraft Moving Horizon
High 15.50 15.28
Low 23.22 28.84

Lanne 9. Mean rates of ranges of pitch attitude (de-
grees) during descending turns.

An analysis of variance indicated a significant
nteraction between pilot experience level and

instrument type, F (1, 30)=11.50, p<.005. A
simple effects test showed that the high experi-
ence group demonstrated significantly smaller
ranges of pitch change with the moving horizon
indicator than did the low experience group,
F (1, 60) =40.23, p<.001. The high experience
group was also superior with the moving-aircraft
indicator, F (1, 60) =13.03, p<.001. There were
no significant differences between the two indi-
eators for the high experience group, but the low
experience group did significantly better with
the moving-aircraft indicator, F (1, 30) =21.31,
p<.001. The interaction is graphically illus-
trated in Fig. 10.

a)
Sty 30
Ee 0
a> —_—
-_
bo .001
20 .00l
Wo
OE —_——
26
«xs 10
2 lon —— HIGH EXPERIENCE GROUP
ra ——LOW EXPERIENCE GROUP
us fl n
=a
< MOVING MOVING
AIRCRAFT HORIZON
INDICATOR —‘ INDICATOR

Figure 10. Mean range of pitch changes during de-
scending turns (confidence levels of significant dif-
ferences are indicated where applicable).

The results may be summarized as follows*:

Roll Recoveries.

(1) Reversals (initially increasing bank angle
while attempting to return to level flight): (a)
there was no diiference between attitude indi-

‘Nore: The summations given in this section refer to
findings whose validity is based on the use of accepted
statistical testing methods.

Differences in performance are expressed only where
they were statistically significant at the 05 level of
confidence or higher and not on the basis of the size of
the numerical difference between the mean values.

Performances are expressed as being equal, compar-
able or identical when there was no statistically sig-
nificant difference between the means regardless of the
size of the numerical difference and in which direction
it was weighed.



Essentially, this indicates that use of the
moving-aircraft indicator provided comparable
or better performance in approximately 27% of
the comparisons, the moving-horizon indicator
provided better performance in about 23%, and
in the remaining 50%, there was little reason to
prefer one indicator over the other. However,
it should be pointed out that these performance
percentages represent a highly simplistic over-
view of the results of this in-flight study and it
is evident that the results were mixed and that
interactions took place which related to various
combinations of type of attitude indicator used,
pilot experience and type of maneuver performed.

Unfortunately, there is no way of knowing
whether the different display pitch ratio in the
moving-aireraft indicator contributed to im-
proved pitch control performance by the low
experience group. It is doubtful, however, that
pitch performance was affected, since the high
experience group showed no similar increase in
pitch control performance when using the
moving-aircraft indicator. The subjects’ lack of
familiarity with the moving-aircraft indicator
may have contributed to low performance results
with this instrument. Also, high experience
pilots may have been so accustomed to the use of
the older type indicator that it was more difficult
for them to readily use the new (moving-aircraft)
type indicator. Too, the existence of real ac-
celerations and their resultant cues during flight
may have induced results different from those
which might be found in ground-based simulator
studies.

Our inability to find conformity between our
data and that from previous studies indicates a
need, perhaps, for some additional research on
the subject. As pointed out previously, the de-
sign of the two attitude indicators was not the
same. The aircraft symbol and bank angle in-
dices in the moving-aircraft indicator were much
smaller than those on the moving-horizon indi-
rator (Fig. 2); also, the indices were located
below the aircraft symbol instead of around the
upper periphery of the instrument case as in the
zontemporary indicator.

Because of space limitation, the size of the
iircraft symbol in moving-aircraft attitude in-
licators has to be smaller (A, Fig. 2) than the
symbol (B, Fig. 2) in the moving-horizon indi-
sator. To provide a larger aircraft symbol, a

change would have to be made in the basic con-
cept and operation of the moving-aircraft atti-
tude indicator design so that the aircraft symbol,
while moving in roll, would remain centered on
the face of the instrument (A, Fig. 11); and the

c

@

Froure 11, Attitude indicator display proposed by
Hasbrook is based on theory that man prefers his
visual frame of reference (horizon bar, in this case)
to remain normal to his head axis and parallel to a
plane drawn through his eyes. Large aircraft symbol
(A) is centered on dial face and moves rotationally
to indicate bank. Horizon (B) remains horizontal
but moves vertically to indicate pitch changes (air-
craft is shown pitched up 10°). Bank angle pointer
(C) moves to left in left turn and to right in right
turn.

horizon bar, while maintaining a horizontal re-
lationship with the instrument face, would move
vertically to depict pitch changes (B, Fig. 11).

This design concept would permit the use of
the larger size symbol characteristics of the
moving-horizon indicator while also providing
the desired outside-in movement relationship ad-
yocated by many researchers.

In reviewing past studies on attitude indi-
cators, it became evident that the design and use
of the moving-horizon indicator was predicated
primarily on the assumption that the real horizon
moves visually in respect to the pilot’s eyes dur-
ing banked turns. In fact, a conversation with
General James H. Doolittle (U.S.A.F. Ret.)
brought out the point that as far back as 1928
(when the first. attitude indicator was conceived
by Doolittle and produced by Elmer Sperry, Jr.),

18



ACKNOWLEDGMENT

The authors wish to express their appreciation for the valuable assist-
ance provided by the pilot subjects, as well as that of Mr. William Flores
who produced many of the illustrations contained in the report.





variations in initial bank angles. Individual
recovery rates were calculated by dividing the
initia) bank angle by the time (to the nearest
quarter second) required to bring the aircraft
to an effective and constant wings-level attitude.
For those subjects who failed to establish a rela-
tively precise wings-level attitude, the total
period was based on a time point after which no
further bank corrections were made by the
subject.

The mean rates of bank angle recovery are
presented in Table 3.

Analysis of variance showed a significant in-
teraction between pilot experience and type of
attitude indicator, F (1, 30)=10.00, p<.005.
There was also a significant three-way interac-
tion, F (1,30) =5.48, p<.05. A simple effects
test of pilot experience by attitude indicator in-
teraction showed that three of the four compo-
nent comparisons were significant. Only the
performance by the low experience group on the
two types of attitude indicator failed to be sig-
nificantly different. The interaction is shown in
Fig. 7.

TOP
oO
a .
)
© 6.0F 2
WwW
2
& 5OP .001
Ww
3 .005
Q 4.0F
my _-—-—
w
°
wy BOF
= ——= HIGH EXPERIENCE GROUP
ac —-— LOW EXPERIENCE GROUP
° I it
MOVING MOVING
AIRCRAFT HORIZON
INDICATOR INDICATOR

Ficure 7. Mean rate of recovery from established bank
angles (confidence levels of significant differences are
indicated where applicable).

The results of the simple effects test of the
three-way interaction have been tabulated by
component comparisons in Table 4.

The panel components of the interaction can
probably be ignored for practical purposes since
they may represent an overlap from the other
combinations—especially since there was no sig-
nificant panel effect. Furthermore, the panel
variable did not show a primary interaction with
either of the other two variables.

Pitch Control During Recoveries. Initial
pitch attitude (at the time control was given to
the subject) was not systematically, nor pre-
cisely, controlled by the safety pilot; but there
is no indication of systematic bias relative to
magnitude or direction. The mean for all initial
pitch attitudes was 3.53° from level flight; the
algebraic mean was 0.66° nose-down.

Pitch control was measured by two criteria.
One quantified the excess pitch movement of the
aircraft. Excess pitch was defined as the total
range of pitch change made during each recovery
minus the amount which would have established
a stabilized, level pitch attitude. The second
performance criterion related to the rate at which
pitch attitude was changed to obtain a stabilized
pitch condition.

The results for excess pitch movement are
presented in Table 5.

| ATTITUDE INDICATOR
Experience Moving Aircraft Moving Horizon
Full Panel | Part Pane! | Full Panel | Part Ponel
High 3.19 3.21 2.59 2.64
Low 5.85, 4.35 8.61 9.73

Taste 5, Mean rates of pitch movement (in degrees)
in excess of required pitch correction to establish
effective control of aircraft.

An analysis of variance indicated a significant
interaction between pilot experience and type of
attitude indicator used, F (1, 30) =14.53, p<.001.
A simple effects test indicated that the low ex-
perience group made significantly larger excess
pitch corrections than did the high experience
group when the moving-horizon indicator was
used, F (1, 60) =45.71, p<.001. However, the low
experience group made significantly smaller ex-
cess pitch corrections with the moving-aircraft



cators for either experience group; (b) there was
no difference between groups when using the
moving-aircraft attitude indicator; (c) when
using the moving-horizon attitude indicator, the
low experience group made more reversals than
did the high experience group.

(2) Recovery of first 10° of bank: use of the
moving-horizon indicator resulted in faster re-
coveries regardless of pilot experience.

(3) Roll recovery rate: (a) the subjects with
high experience recovered to level flight at a
faster rate than did the low experience group
regardless of type of attitude indicator used;
(b) the high experience group achieved level
flight at a faster rate with the moving horizon-
indicator than it did with the moving-aireraft
indicator; (c) the subjects with low experience
achieved level flight at the same rate regardless
of type of attitude indicator used.

(4) Excess range of pitch changes: (a) per-
formance of the high experience group was equal
regardless of type of attitude indicator used;
(b) the low experience group had less pitch
change with the moving-aircraft indicator than
with the moving-horizon indicator; (c) there
was no difference in performance of the high and
low groups when utilizing the moving-aireraft
indicator; (d) the high experience group had
less pitch change than did the low experience
group when using the moving-horizon indicator.

(5) Pitch change rates: (a) the two attitude
indicators provided equal performance; (b) the
high experience group attained a faster rate than
did the low experience group regardless of the
attitude indicator utilized.

Performance During Alternating Turns.

(1) Bank angle performance: the data was
too inconsistent to provide meaningful evalua-
tion.

(2) Pitch control: (a) pitch excursion range
was less for the high experience group than for
the low group when the moving-horizon indi-
eator was utilized; (b) pitch excursion range
was the same for both groups when the moving-
aircraft indicator was utilized; (c) the low ex-
perience group had less pitch excursion when
using the moving-aircraft indicator than when
using the moving-horizon indicator; (d) pitch
excursion range of the high experience group
was equal for both attitude indicators.

12

Performance During Descending Turns.

(1) Bank control: there were no differences
between indicators or experience groups.

(2) Pitch control: (a) the high experience
group had less pitch excursion than the low ex-
perience group regardless of the attitude indi-
cator utilized; (b) the low experience group had |
less pitch excursion with the moving-aircraft)
indicator than with the moving-horizon indi- |
cator; (c) the high experience group had the:
same excursion range regardless of the attitude,
indicator utilized. 1

V. Discussion

The results of this in-flight study are some-
what surprising in relation to findings from
previous research on the relative merits of inside-
out and outside-in attitude indicators. Data
from many of these earlier studies suggest that
the outside-in (moving-aircraft) indicator pro-
vides better pilot performance; but this in-flight
study fails, in the main, to show any such well
defined, overall advantage.

In general, of the twenty-two performance
comparisons in which statistical significance was
.05 or better, there were only six in which the
moving-aireraft indicator provided comparable
or better performance than did the moving-
horizon indicator, Five of these related to pitch
control performance. Interestingly, in three of
the five, the improvement was related to per-
formance of the low experience pilot group.

In another eight comparisons, performance
was comparable regardless of which type of in-
dicator was used; of these eight, four related tc
pitch control and the other four to bank control.
In three of the remaining eight comparisons, the
high experience group demonstrated better per-
formance with the moving-horizon indicator thar
did the low experience group; two of these re
lated to pitch control and one to reversals. Ir
another three, the high experience group per
formed better than the low group regardless o:
the type of indicator used; two of these thre:
related to pitch control, and one to bank control
Of the two final comparisons, the moving
horizon indicator provided better bank contro
performance within the high experience grou)
than did the moving-aircraft indicator, In thi
group of eight comparisons, four related to pitel
control and four to bank control.