The concept of a cockpit display of traffic information (CDTI) includes the integration of air traffic, navigation, and other pertinent information in a single electronic display in the cockpit. Concise display symbology was developed for use in later full-mission simulator evaluations of the CDTI concept. Experimental variables used included the update interval motion of the aircraft, the update type, (that is, whether the two aircraft were updated at the same update interval or not), the background (grid pattern or no background), and encounter type (straight or curved). Only the type of encounter affected performance

Baty, D.

Jago, S.

Oconnor, S.

Palmer, E.

English

NASA Technical Reports Server

_" i NASA Technical Memorandum81171
: (NASA-TS-811711 EFFECT U9 DISPLAY UPDATE Nai-29127
'_ i I'_TERVAL, UPDATE TYPE, AND BACKGBOSgD ONi'ERCEPTION OF AIRCBAFg SEPARATION ON A
:-_i COCK_IT DISPLAY ON TRAffIC IN¥O_gATZO_ Uncia5
e. ! {NASA) 12 p HC AOI/MF A01 CSCL 01D G3/06 2'7105
,_' Effectof DisplayUpdate Interval,
Update Type, and Background on
_. Perceptionof AircraftSeparation
_ on a Cockpit Displayof Traffic
., Information
i
Sharon Jago, Daniel Baty, Sharon O'Connor and ,
EverettPalmer
June 1981 t_-_¢-_.v-"-%'_\"_'<'';_.. "_
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1981020589
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• NASA Technical Memorandum 81171
Effectof DisplayUpdate Interval, ,:_
Update Type, and Background on
Perception of Aircraft Separation
on a Cockpit Display of Traffic ,/
Information _,
Sharon Ja_.lo,San Jose State University, San Jose, Californ,a l'-
Daniel Baty, Ames Research Center, Moffett Field, California
Sharon O'Connor, Sail Jose State University, San Jose, Cahfornia t.
and
Everett P,dmer, Ames Research Center, Moffett Field, California
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Ames Research Center
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1981020589-002
bEFFECT OF DISPLAY UPDATE INTERVAL, UPDATE TYPE, AND BACKGROUND ON
PERCEPTION OF AIRCRAFT SEPARATION ON A COCKPIT DISPLAY
") OF TRAFFIC INFORMATION
-" Sharon Jago,* Daniel Baty, Sharon O'Connor,* and Everett Palmer
:\ Ames Research Center
The concept of a cockpit display of traffic information (CDTI) includes
the integration of air traffic, navigation, and other pertinent information in
a single electronic display in tllecockpit. The present study was conducted
as part of a research project designed to develop clear and concise display
symbology for use in later full-mlssion simulator evaluations of the CDTI con-
cept. This experiment required test subjects to monitor a CDTI and to make
perceptual judgments about the future position of an intruder aircraft in
relationship to their own aircraft. Experimental variables used in the study
included the update interval motion of the aircraft, the update type, that is,
whether the two aircraft were updated at the same update interval or not, the
background (grid pattern or no background), and encounter type (straight or
curved). Results indicated that only the type of encounter affected
performance.
INTRODUCTION
Projected estimates of air traffic indicate a marked increase that is
expected to create a demand for improved air leaffie control services to main-
lain or improve present levels of safety. The concept of a cockpit display of
traffic information (CDTI) is being considered to determine whether such a
display could |lave a beneficial role in the air traffic system. A CDTI shows
the pilot the position of another aircraft, in relation to the pilot's own
aircraft (herein referred to as "ownshlp") on a moving map display. This
disp]ay also indicates the pilots o_m position and direction of travel with
respect to ground-referenced area-navigation routes and terrain features,
Objects on the display move down the display at a rate proportional to air-
craft movement over the ground.
Prior experiments in this project were directed toward developing a clear
i and easy to use display symbology CDTI (refs. l, 2). These studies dealt with
some basic factors affecting pilot perception of motion and traffic separation,
'_ Pilots made Judgments while monitoring a dynamic CDTI display. Errors in
Judgment were recorded to determine how accurately pilots could predict the
future separation between their own aircraft and an intruder aircraft. The
_San Jose State University, San Jose, California
" i
1981020589-003
main concern of this paper is how various ways of updating information on the
i CDTI may affect the pilot's ability to use that information. Ownship transla-
tlon, rotation, and updating can be continuously updated if the information
comes from an on-board area-navigation system. Continuously updated informa-
tion is necessary if the dlsplay is to be used for guidance and control of the
: ownship. The ownship and intruder can only be updated once every 4 sec, if
all the information is transmitted to the aircraft from ground radar. Discrete
_" " updating may cause fewer perceptual errors. When updating is not continuous
the symbols seem to "Jump." These jumps may be useful in estimating relative
"" motion.
Three types of updating of the two aircraft symbols were investigated in
.4 this study. With one type, the rotation would update I0 times/sec, with the
ownship and intruder updating and translating once every 4 sec. This updating
type was used in the previous experiments; it allows the relative motion to be
estimated when both positions update together. With the heading of the own-
ship continuously updating, the display can be used for heading control. In
the second type of updating, the rotation and translation are the same, with
both the ownship and intruder updating once every 4, 2, I, or 0.I sec. This
is perhaps perceptually the cleanest type of updating, with the ownship and
intruder always updating simultaneously. This would be the kind of informa-
tion provided by data link from the ground. In the third type of updating,
the ownship rotation and translation updates once every 0.1 sec, and the
intruder's position updates once every 4, 2, or I sec. In this case, the
ownship position and heading are assumed to be available from an on-board area
navigation unit and therefore continuously available. This should result in
the best control of the ownship. This type could cause a perceptual illusion.
The continuous relative motion may not be perceived with the large discrete
update of Just the intruder.
Background information (route, terrain features, etc.) provides a frame
of reference that allows the pilot to separate intruder movement relative to
the ground from movement relative to the ownship. In previous studies naviga-
tion routes were displayed for reference; in this study there was a rectilinear
grid background or no background at all.
The objective of this experiment was to see if there were significant
differences in performance on a perceptual task of aircraft separation with
different update intervals, update types, and backgrounds.
METHOD
Display Hardware
The CDTI was displayed on a 18- by 18-cm CRT located directly below the
altitude indicator in a flxed-base cockpit simulator. The center of the dis-
play was located 25° (0.44 rad) below the horizontal and 0.87 m from the
pilot's eye-reference point. The display symbols were generated by a general
24 _
f,
1981020589-004
, purpose, stroke-writing computer graphic system. The green phosphor on the
CRT left no noticeable afterglow.
i_ Disp.!,._y Symbology
Figure 1 shows display formats used in this experiment. A chevron symbol
: for the ownship and a circular symbol for the intruder aircraft remained con-
:I stant throughout the experiment. The_e symbols were preferred by the most
pilots in Hart's study of pilot opinion on various types of CDTI symbolsf
(ref. 3). The top point of this symbol indicated the actual location of the
--- ownship. The intruder was displayed by a circular symbol, with the present
_/ location at the center of the circle. Neither symbol included predictors on
or history of previous motion. All subjects received practice trials with the
_" symbology. The width of the terrain displayed on the CRT was I0 n. ml. With
this map scale, which seem.qreasonable for terminal-area operations, I n. ml.
on the ground equals 1.2 cm on the display. No sensor noise or tracker lag
was simulated for these tests.
=
©
\
NO BACKQROUND GRID BACKGROUND ' ,_
Figure I.- Display format used in experiment. ,;
Figure 2 shows the eight parameters that were used to specify an encounter ':
between the ownship and an intruder. The encounter variables included viewing
time, miss distance, and type of encounter. The viewing time for the experi-
ment was 16 sec. The encounter began at 44 sec and ended at 28 sec before the
point of closest encounter. In all the encounters the miss distance was
3000 ft. There were no encounters that would result in a collision. For each i
display condition, the subjects monitored 24 encounter situations. In 12 of
these encounters, the intruder would ultimately pass in front of the ownship.
Figure 3 depicts those 12 encounters and the parameters as they would appear
if they were displayed with ground-referenced predictor and history. The i
remaining 12 encounters differed in that the intruder would pass behind the !
ownship. In 12 encounters both aircraft were going straight, and in the _:
remaining 12 one or both aircraft were turning. During the experiment, the !
order of presentation was randomized by the computer. In addition, whether I_
the subject saw the encounter or its mirror image was also randomized by the {"
computer. !_i
I!
3
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' _
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2
1981020589-005
s_ , !
.\ , _ v. _l
,[
'// R
Vo, eoSEPARATION R
RELATIVEBEARING Sr
RELATIVEHEADING _r t
SPEED Vo,VI
TURNRATE _o' _1
TIME TO ENCOUNTER t
Figure 2.- Eight parameters used to specify an encounter.
Independent Variables
For the experiment, the update intervals of the ownship and intruder were
varied. The different update intervals were: once every 4, 2, i, and 0.I sec.
Three update types were used: (I) rotation was 0.I sec (continuous) with the
ownship and intruder updating and translating every 4 sec; (2) rotation and
translation were the same for both the ownship and intruder with the rotation
and translation updating either every 4, 2, i, or 0. I sec; and (3) rotation and
translation continuously while the intruder was different (every 4, 2, or
0.I sec). The display had two background conditions: a grid or no background.
Task
The subject's task was to monitor the CDTI display and to predict whether
the intruder aircraft would pass in front of or in back of the ownship. Each
trial was started by the subject pushing a button. After 4 sec, the intruder
appeared on the CDTI with a position, velocity, track angle, and turn rate
calculated so that the intruder would be either directly in front of or in
back of the ownshlp in 44 sec. After viewing the encounter for 16 sec, the
CDTI blanked and was replaced by a message asking whether the intruder would
pass in front of or in back of the ownship. The subject pushed a hand-held
instrument to make his choice of four posslbilities: positive in front, guess
in front, guess in back, or positive in back. The words "IN FRONT" or "IN
BACK" then appeared indicating the correct response. Although data were
/
/ 4
j
1981020589-006
't "_
I
i i J,
01_---o 00 0i 00____ :
eee _"
\ l
' " " ;
" 1 3 5 7 _ _
Or = -90° Or = -45° Or = -135 ° Or = -90° "
-_ V! = 200 knots VI = 200 knots V! = 200 knots V! = 133 knots .:
4o = O°/sec _.o= O°/sec 4o = O°/sec _o = °°/sec
; _l = O°/sec ¢e = O°/sec _a = O°/sec _l = O°/sec _;
i
ej
: " _
#
9 11 13 15 :,
_, = -90° _t = -90° Or = -90° Or = -90 ° )
Vt = 300 knots VI = 200 knots VI = 200 knots VI = 200 knots ;
_.o--°_V'_c _.o=-_'5°°/'_° _.o--°°/s_° _.o=""'SO°/se'_ i
QI = O°/sec 41 = O°/sec ¢1 = -l'50°/sec ¢'1 = O_'/sec
|1 •
•e
17 19 21 23
_ =-90° ¢, =-90° ¢, =-90° Or = -90°
'" VI = 200 knots VI = 200 knots VI = 167 knots VI = 200 knots
_0 = O°/sec _.0 = -l"50°/sec ¢0 = O°/sec ¢0 = +l.50"/sec
_1 = +l'50°/sec ¢l = -l'50°/sec _'1 = O°/sec _'1 +l,50"/sec
/ Figure 3.- Twelve encounters u_ed In experiment shown wlth curved ground-
/ referenced predictors and history (predictors and history were not used
/ in this study). _:°
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1981020589-007
_ i'i
f
collected for all four choices, the data were collapsed over "positive" and
. "guess," It was felt that subjects were developing response patterns and were
not really able to respond to the four choices,
Subjects
_" Four students served as paid subjects for this experiment. Because the
experiment involved a perceptual task that required no flight experience, it%
was not felt necessary to use pilots as subjects. One of the subjects had
. participated in an earlier experiment in which CDTI symbology was used.
•, Experimental Design
The experiment was run with the subjects participating two at a time over
a 2-day test period; the testing days were consecutive. Each subject viewed
the CDTI on a separate CRT. The response of one subject was unknown to the r
other. Subjects used the same simulator seats throughout the experiment.
Oral instructions were given. Approximately 30 min were spent describing i_
the task and training the subjects on the interpretation of the different dis- I;
play symbology. !,!
RESULTS
Table I shows the percent error made for each update interval, update
type, and background. The data were averaged over subjects. The results
show little difference between the different experimental conditions.
I
TABLE I.- PERCENT ERROR ACROSS SUBJECTS FOR I_[:
STRAIGHT AND CURVED ENCOUNTERS_ I_
Encounter ....
Straight Curved
J
Update intervals/sec ,
Update type 0.I I 2 4 J 0.I I 2 4 i,
I
With grid
Update same 40 22 32 34 42 38 42 40
Update different 40 34 38 42 30 38
Rotation continuous 18 34
Without grid
+,
_ Update same 36 16 12 16 34 32 30 40
Update different 40 30 46 38 42 42 ;
Rotation continuous 18 34
/ ..... ;
,/ aEach cell represents 96 trials. _°
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1981020589-008
'.3
An ANOVA on the error rate was calculated, and the only significant dlf-
! ference was between straight and curved encounters (F(I,2) = 15.90, p < 0.025).
Table 2 shows the results of the ANOVA.
•TABLE 2.- ANOVA FOR BACKGROUND (A), UPDATE CONDITION (B),
_ AND TYPE OF ENCOL_TER (C)
t_
Source SS df MS F
_, A (background) 4.13 1 4.13 6.35,a
: • B (update condition) 46.05 7 6.58 1.81b
• C (encounter type) 21.94 I 21.94 15.90c
, S (subjects) 2.46 3 .82
+:_, AXS 1.96 3 .65
BXS 76.23 21 3.63
CXS 4.15 3 I.38
AXB 20.69 7 2.96 I.44b
AXC .64 I .64 <I
BXC 20.38 7 2.91 I.95b
AXBXS 42.97 21 2.05
AXCXS 7.09 3 2.36
BXCXS 31.28 21 I,49
AXBXC 8.91 7 1.27
AXBXCXS 56.II 21 2.67
=
Up < 0.10
bp < 0.25
Op < 0.025
Multlple comparisons were conducted comparin8 the different update inter-
vals, update types, and backgrounds; none of the comparisons indicated a
," significant difference. Table 3 shows the results of the comparisons.
TABLE 3.- PLANNEDCOMPARISONS FOR UPDATE INTERVALS (A),
UPDATE TYPE (B), AND BACKGROt_D (C)
Source SS df MS ¥
,, ! , • i J
A at Bx/C 1 12.75 3 4,25 <1
A at B_/C 1 10.5 2 5.25 <1
. A at B1/C 2 21.0 3 7.0 1.33
r; A at B2/C 2 8.17 2 4.09 <1
i B at A_/C; 18.5 2 9.25 2.18u
:" _ B at A_/C2 35.17 2 17.59 2.22 a
/.//i ap < 0.25
4 _
_ 7
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1981020589-009
%.
i
In addition, subjective information was collected from the subjects in
the form of a questionnaire at the end of the experiment. The results indl- I
cated that generally the subjects preferred a background grld over no back- , :
ground. The update intervals most preferred was the condition in whlc_ the I
update intervals were the same for both ownshlp and intruder. There was no
consensus on update types. )
DISCUSSION ,
As indicated in the analysis of the data, the different update intervals,
i update types, and background conditions did not significantly effect the _;
j ability of the subjects to accurately Judge separation. A significant differ-
ence was found between straight and curved encounters. This finding supports
] previous studies (refs. I, 2) in which it was found that fewer errors were
made with straight encounters.
It is known that subjects exhibit a wide range of individual differences _
in perceptual, motivational, Judgmental, and learning abilities. Statistical
results from this experiment indicate that a large portion of the total vari-
ance may be accounted for by individual differences. The fact that the
statistical analysis showed no difference in performance while subjective
results from _he questionnaire show a marked difference in preferences indi-
cates that this study is also marked by individual differences. The results
seem to indicat:e that variables such as update intervals an_ background do
, not significantly change performance although personal preference can be a
factor.
CONCLUSIONS
This experiment is one more in a series of experiments designed to eval-
uate CDTI symbology in a dynamic but controlled environment. Two general
' observations are based on the study results: (I) the different update inter-
vals, update types, and background did not effect perceptual Judgment; and
(2) prediction is more difficult with encounters in which one or both aircraft
are turning.
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1981020589-010
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F__ ._
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REFERENCES
I. Palmer, Everett; Baty, Daniel; and O'Connor, Sharon: Perception of Air-
craft Separation with Various Symbology on Cockpit Display of Traffic
Information. Paper presented at the 15th Annual Conference on Manual
_ Control, Wright State University, Dayton, Ohio, March 1979.
_" ' 2. O'Connor_ Sharon; Palmer, Everett; gaty, Daniel; and Jago, Sharon: I,.
_\ Effect of Viewing Time, Time to Encounter, and Practice on Perce!r.,'_
.. of Aircraft Separation on a Cockpit Display of Traffic Informatio..
NASA TM-81173, 1980.
L
_ 3. Hart, S. G.: Content of S>mbology and Format of Cockpit Di_,.lay of
Traffic Information: Pilot Opinion. Paper presented a.. the 15th
Annual Conference on Manual Control, Wright State University, Dayton,
Ohio, March 1979.
i
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Effect of display update interval, update type, and background on perception of aircraft separation on a cockpit display on traffic information

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