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Driskill, W.E., Weissmuller, J.J., Quebe, J., Hand,
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http://bluecoat.eurocontrol.fr/reports/.

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Hooper, E.Y. & Coury, B.G. (1994). Graphical displays
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Jensen, R.S. (1982). Pilot judgment: Training and evalu-
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Administration, Office of Aviation Medicine,
Washington, D.C. NTIS # DOT/FAA/PM-86/43.

Kleinmuntz, D.N. & Schkade, D.A. (1993). Informa-
tion displays and decision processes. Psychological
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on Aviation Psychology, Columbus, OH: The Ohio
State University, 152-7.

Shepard, R.N. & Metzler, J. (1971). Mental rotation of
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‘Weigmann, D.A. & Shappell, S.A. (1997). Human
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‘4rU.S. GOVERNMENT PRINTING OFFICE: 1998 - 660-088/60068


with the text-only method, the asterisk indicates the
nearest airport. Again, the participant would press the
direct-to button and then press the 4 0’clock position
on the circle.

The third method for presenting nearest airport
information is shown in Figure 5. In this method, the
nearest airports are shown in a map display, with an
asterisk positioned next to the closest airport. In the
example shown, the aircraft is on a heading of 165
degrees. The nearest airport, OK09, is at a bearing of
240 degrees, or 75 degrees to the right of the current
aircraft heading. This corresponds to a position be-
tween 2 and 3 o’clock from the current aircraft heading.

For each of the trials, two types of data were
collected. One was the difference between the actual
relative direction to the nearest airport (i.e., the o’clock
position) and the indicated relative direction to the
nearest airport, measured in degrees. The other was
the response time for indicating relative direction,
measured in milliseconds from the time that the
nearest airport information was first presented on the
display. In addition, the number of practice trials

required for each of the combinations of presentation
mode (text-only, enhanced-text, map) and map mode
(track-up, north-up) was recorded.

RESULTS

Verbal Test of Spatial Abilities

An analysis of the spatial abilities test scores did not
reveal any differences in spatial abilities among any of
the participant groups. In addition, when the spatial
abilities test score was used as a covariate for the
analysis of variance measures, it had no effect on the
results. Therefore, the spatial abilities test was dropped
from the analyses and will not be discussed.

Misorientation Errors

Instead of a direct analysis of the difference be-
tween the actual airport orientation and indicated
airport orientation for each trial, the concept of a
misorientation error was created. A misorientation
error was defined as an error of more than 45 degrees
in judging the relative direction of the nearest airport.

Figure 5. Map method for presenting nearest airport information (north-up mode)


ACKNOWLEDGMENTS

This research is part of the Civil Aeromedical Institute general aviation human factors
research program. Program direction is provided by the Aircraft Certification (Small Aircraft
Directorate, ACE-100) and General Aviation and Commercial Division (AFS-800) sponsors.

The author expresses his appreciation to Jody Worley, for his help in creating the
experimental scenarios and establishing the GPS interface design, and to Howard Harris for
his help in recruiting subjects. The author also thanks Dr. Dennis Beringer for his assistance
in establishing the experimental protocol.

iii


60 ?”
50 WA
40 WA
—
30 ‘South
WA =m =North
20
: A
10 7 TSS 10

2
of te es ee

EText Map

Text

Figure 8. Additional practice trials as a function of presentation mode and aircraft heading

Figure 8 shows the interaction between presenta-
tion mode and aircraft heading on additional practice
trials. As can be seen from the figure, the significant
interaction effect is attributable to the large difference
in practice trials between northbound and south-
bound conditions for the text-only presentation rela-
tive to the other two presentation conditions. This
large difference was due primarily to confusion as to
how to compute relative direction to the airport based
on heading and bearing to the airport. Even if the
participant did not quite grasp the experimental task,
performance was still adequate in the northbound
conditions because relative and absolute directions
were nearly identical. However, this was not so when
the airplane was southbound. In the southbound
condition, an understanding of task requirements was
essential to completing the practice trials.

DISCUSSION

Taken as a whole, these results make a strong
argument against use of a text-only, tabular display of
nearest airport information. Approximately three times
as many misorientation errors occurred using the text-
only display than with either of the other two display
conditions (62 for text-only, 23 for map, 17 for
enhanced-text). In addition, participants, on average,
were twice as slow using the text-only display than
with either of the other two display methods — a full
5 seconds slower on average. Finally, most of the
additional practice trials occurred under the text-only
condition. One interesting note was the lack of a
difference in speed or accuracy under the text-only
condition between pilots using the simulator and
pilots not using the simulator. This suggests that even
when a heading indicator was available, pilots did not

12

use it for deciding relative direction. Post-experimen-
tal questioning confirmed that most of the pilots did
not make use of the heading indicator for deciding
relative direction. A failure to cross-reference the GPS
display with the other available instruments could
simply be a result of the laboratory setting; however,
it could also indicate that pilots tend to become
fixated on the GPS display and fail to scan properly,
a tendency noted in an earlier study of GPS use
(Wreggit & Marsh, 1996).

A second important finding was that participants
using a north-up display were three times as likely to
commit a misorientation error as participants using a
track-up display. Among only the pilots, four times as
many errors were committed using a north-up display
as the track-up display (eight vs. two respectively). In
addition, participants were significantly slower using
the north-up display than the track-up display (6332
msec. vs. 4629 msec., on average). Finally, four times
as many practice trials were required with the north-
up display than with the track-up display. While all of
this is strong support for the use of track-up displays
over north-up displays, there could be situations where
a world-referenced coordinate system (i.e., north-up
display) would be more beneficial to the decision-
making process than an egocentric system (such as is
found with a track-up display). The decision as to
which map display is the most effective could depend
on what kinds of information are being integrated
with the display.

Finally, the use of an enhanced-text display, while
clearly superior to a text-only display, did not appear
quite as effective as the map display. Though there was
nota significant difference between the enhanced-text
and map displays, there was a tendency for confusion
over whether the symbol was north-referenced or


Facilities

Data collection was performed using the Basic
General Aviation Research Simulator (BGARS) lo-
cated at the FAA Civil Aeromedical Institute in Okla-
homa City. BGARS is a medium-fidelity, fixed-base,
computer-controlled flight simulator. The controls
and displays used in the BGARS for this study simu-
late those of a Beech Sundowner. Control inputs are
provided by high-fidelity, analog controls, including
a damped and self-centering yoke, navigation radio
frequency selection module, rudder pedals, throttle,
gear, flap, and trim controls. Instruments are dis-
played on a CRT and react in real time to control
inputs and aircraft conditions. The external views
consist of a 50-degree forward-projected view, two
smaller right-side-view CRTs, and two smaller left-
side-view CRTs. A GPS display was hosted on a 10-
inch, True Point, touch-screen panel located just to
the right of the pilot position and within easy reach of
the pilot. Participants interacted with the panel using
only their right hand. One group of 12 participants
operated the simulator while interacting with the GPS
display. The other two groups of participants sat in
the pilot position while interacting with the GPS, but
they did not operate the simulator.

Experimental Design

Four factors were manipulated in the experiment:
1) Participant type (pilot/no sim, pilot/sim, and non-
pilot); 2) nearest airport information display mode
(text-only display, enhanced-text display, map dis-
play); 3) map display mode (north-up or track-up);
and 4) aircraft heading (generally north or generally
south), resulting in a 3x3x2x2 experimental design.
Participant type was a between-subjects condition,
while the other three conditions were within-subjects.
Dependent variables that were collected included ori-
entation response time, orientation response accu-
racy, number of additional training trials required for
each condition, and score on a verbal test of spatial
abilities (Ackerman & Kanfer, 1993).

Design of Trials

Four aircraft headings were used in the experimen-
tal trials. Two headings were for the generally north
condition (345 degrees and 015 degrees), and the
other two headings were used in the generally south
condition (165 degrees and 195 degrees). In addition,
four pairs of airports were selected from a navigational
chart of the Oklahoma area for use in the experiment.

Two of the airport pairs were located east and west of
each other, the other two pairs were located north and
south of each other. Each airport was approximately
20 miles from its pair. No airport was located close to
a large metropolitan area.

For each airport pair, for each aircraft heading, four
aircraft positions were selected that met the following
conditions: 1) the position was approximately half-
way between both airports, but definitely closer to one
airport than the other; and 2) the direction to the
closest airport corresponded to one of four clock
directions relative to the aircraft consisting of either
the 1, 4, 7 or 10 o’clock positions or the 2, 5, 8 or 11
o'clock positions. For two of the airport pairs, the
clock directions were 1, 4, 7 and 10 o’clock, for the
other two pairs, the clock directions were 2, 5, 8 and
11 o’clock. The total number of positions selected was
4 (airport pairs) x 4 (headings) x 4 (clock positions) =
64 positions. From these 64 positions, 48 were se-
lected at random for each subject to be used as experi-
mental trials. The positions were selected randomly
with the constraints that half were north and half were
south aircraft headings, and for half of the north and
south trials the relative direction of the nearest airport
was in front of the aircraft (the 1, 2, 10, or 11 o’clock
positions) and for the other half the relative direction
of the nearest airport was behind the aircraft (the 4, 5,
7 or 8 o'clock positions).

Half of the 48 experimental trials were used for
actual data collection, the other half were used for
participant practice. During the experiment, partici-
pants were exposed to 24 actual trials, representing
two repetitions of each of the 12 possible within-
subject conditions. The number of practice trials the
participant was exposed to depended on performance,
with the minimum number of practice trials set at 36,
so that some of the practice trials were used more than
once for each participant.

Procedure

Participants were tested individually. The participant
received a consent form to read and sign and then
completed an experience questionnaire. Questions gauged
the participant’s age, gender, handedness, educational
level, flight experience, and GPS experience. Following
completion of the questionnaire, the participant per-
formed a verbal test of spatial abilities (see Ackerman &
Kanfer, 1993). After completing this test, the participant
was seated at the simulator, and an explanation of the
experimental task was presented. During the actual


GPS Desicn ConsIDERATIONS:
DispLayING NEAREST AIRPORT INFORMATION

PURPOSE

This research is part of a multi-task approach to
develop and test interventions that will mitigate or
eliminate root causes of general aviation (GA) pilot
errors and thereby achieve a reduction in general
aviation accidents and incidents. The title of the
overall research project is “General Aviation: Devel-
opment and Assessment of Flight Systems Innova-
tions.” Human factors information and data gained
via this research will provide a sound scientific basis
for the Federal Aviation Administration and the GA
Industry Coalition to develop and execute certifica-
tion and rule-making initiatives that will result in
gains in general aviation safety.

INTRODUCTION

Global positioning system (GPS) receivers are be-
ing incorporated at a rapid pace into today’s general
aviation aircraft. While human-interface design stan-
dards exist for GPS receivers (FAA, 1995), these
standards do not precisely define how information
should be presented to the pilot or even what informa-
tion should be presented. There have been some
preliminary studies addressing the human factors as-
pects of GPS design (Heron, Krolak & Coyle, 1997;
Nendick & St. George, 1995; Wreggit & Marsh, in
press), but many issues remain to be explored. A case
in point is the display of nearest airport information.
Most GPS units today have a function for displaying
the nearest waypoints to the current position of the
aircraft. The types of waypoints that can be displayed
include very high frequency omnirange (VOR) facili-
ties, nondirectional beacons (NDB), navigation in-
tersections, and airports. The use of the nearest
waypoint function for the display of nearest airport
information is relevant to pilot safety considerations,
since this information could likely be used under
emergency and/or distress conditions.

The likelihood of a pilot to make a sound decision
while under stress is dependent upon the quality of
information available. Two components of pilot deci-
sion-making have been identified: cognitive and af-
fective (Brecke, 1981; Driskill, Weismuller, Quebe,

Hand, Dittmar, & Hunter, 1997; Jensen, 1982; Jensen,
Adrion, & Lawton, 1987). Driskill et al. define the
cognitive component as those processes that are used
to establish and evaluate the alternatives in a decision-
making situation. Jensen (1982) suggested that the
cognitive component relates to the pilot’s ability to
search for, and establish, the relevance of all available
information regarding a situation, to specify alterna-
tive courses of actions, and to determine expected
outcomes from each alternative. The ability to select
between alternative courses of actions is critically
dependent on the information available regarding
each of those alternatives. The kinds of information
available, and the way the information is presented,
can alter the decision-making process.

In most current GPS units, nearest airport infor-
mation is displayed in a text-based format, even if the
unit contains a moving-map display. The information
usually given to the pilot includes the airport identi-
fier, bearing to the airport, and distance to the airport,
for the closest 10 to 20 airports from the current
aircraft position. In an emergency situation, a pilot
would use the nearest airport function to locate and
orient to the nearest airport. While it might be as-
sumed that the pilot would simply select the airport at
the top of the list (i.e., the nearest airport in terms of
distance), there could exist circumstances where the
nearest airport is not the best choice. Consideration of
wind, weather, obstacles, traffic, or other factors might
influence the selection process. All of these consider-
ations require that the relative direction of each air-
port from the current aircraft position be known. It is
for the benefit of regulators, manufacturers, and end
users, that we determine the most effective method of
presenting nearest airport information to the pilot so
that relative orientation to each airport can be in-
cluded in the decision-making process.

Since many GPS units have a moving-map display,
it is possible to present airport distance and bearing
information directly on the moving map, rather than
in a text-based tabular format. While there are cur-
rently no studies that have directly compared text-
based vs. moving map-based presentation of orienting




track-referenced (it was, in fact, track-referenced).
This confusion sometimes caused a delay in process-
ing while the symbol was cross-referenced with the
bearing and heading information. It is possible that a
small amount of training could eliminate any confu-
sion regarding the symbol, but this hypothesis re-
mains to be tested.

While it is true that the current research was in-
tended to address a specific design feature found in
current GPS units, the results could be extended to
any generic aircraft navigational display. In determin-
ing the ramifications of any research, it is important to
view the experimental results from a common set of
assumptions. One primary assumption made in the
current research is that the GPS nearest airport func-
tion will be used to presenta set of alternative airports,
possibly under emergency conditions, and that pilots
will select from among the alternatives what they hope
is the best (i.e., closest, safest route, etc.). For most
GPS units currently on the market, assistance regard-
ing orientation to a specific airport, except for bearing
information, is given only after that airport has been
selected and, therefore, after information about any
other alternative has been removed. However, there
are several reasons that airport orientation should be
considered as one of the factors involved in the airport
selection process. The presence of obstacles or the lack
of suitable terrain for making an emergency landing
could mean that flying toward one airport is not as
safe as flying toward a different airport that is only
slightly more distant. In addition, the presence of
even a moderately strong wind could greatly alter the
time it takes to reach an airport that is in the same
direction as the prevailing wind, as opposed to one
that lies in the opposite direction. Recent research by
Weigmann and Shappell (1997) showed that errors in
judgment were more frequently associated with more
serious airplane accidents, while procedural errors
were more frequently associated with minor airplane
accidents. This finding leads us to suggest that we need
to give stronger consideration to the information avail-
able for making in-flight judgments, of which airport
selection during an emergency is certainly an example.

Given that airport orientation should be included
as a part of the decision regarding which of two or
more airports to select, it is clear from the present
study that the use of a text-only tabular display, which
provides only bearing and distance to the airport, is
inferior. However, this still begs the question of which
display is the best. For an analysis of this question, we

must turn to the problem of aeronautical decision-
making that was touched on in the introduction.
Recall that Jensen (1982) posited a cognitive compo-
nent to aeronautical decision-making that relates to
the pilot’s ability to search for and establish the
relevance of all available information regarding a
situation, to specify alternative courses of actions, and
to determine expected outcomes from each alternative.

When we consider the types and amount of infor-
mation presented ona GPS display, we must consider
the tradeoff between the benefit of a more effective
decision and the amount of time and resources re-
quired to make that decision. By providing more
information regarding a set of options we allow for a
better decision-making process to occur. However, if
the time and resources expended by including this
information in the decision delays the time to make
the decision, or causes other relevant and more impor-
tant information to be missed, then the tradeoff is
negative. Kleinmuntz and Schkade (1993) stated that
decision makers engage in a form of cognitive cost-
benefit analysis. Displays influence the anticipated
effort and accuracy of the decision-making process,
and, therefore, influence the strategy adopted in mak-
ing the decision. Recently, Hendy, Liao, and Milgram
(1997) stated much the same idea when they said,
“Humans adapt to excessive processing load by chang-
ing their processing strategy so as to reduce the amount
of information to be processed or to increase the time
available before an action has to be performed.” (p.
32). Applying this concept to the present research, it
is likely that a text-only display of nearest airport
information encourages the pilot to adopt a decision-
making strategy that does not include the comparison
of information from two or more alternative airports.
A likely reason for this is that the time and effort
required to include this information is judged to be
not worth the anticipated benefit.

By making it easier to compare the positions of
several airports, we influence the anticipated effort of
the task, and thereby increase the likelihood that this
position information will be included in the decision
of which airport to select. However, at the same time,
we need to influence the anticipated benefit of the
added information. Two ways this can occur is through
training or experience. If a training program were
established to demonstrate the utility of considering
airport orientation, it might prevent a pilot from
learning the lesson through experience. In aviation,
there are many lessons that are best left to training.


is available in the map display through the use of an
orienting arrow, the text display might be as useful as
the map display. The text display might actually be
superior to a map display that requires mental rota-
tion to compute orientation.

The present experiment was designed to compare
various methods for presenting nearest airport infor-
mation on a pilot’s ability to orient quickly and
accurately toward the nearest airport. In particular, a
question of interest was whether the graphical presen-
tation of that information is superior to a textual
presentation and, if so, whether that advantage could
be eliminated through the inclusion of an orienting
symbol within the text-based display.

Three different methods for presenting nearest
airport information were evaluated. The first method
represents one that is most commonly found in cur-
rent GPS receivers and, for this experiment, was called
the “text-only” method. In this method, airports are
listed, along with the bearing and distance, in a
tabular format on the screen. Pilots must decide the
relative direction to each airport by comparing their
current heading to the listed bearing to the airport. A
cross-check of the heading indicator will aid pilots in
performing this task, if they remember to reference
the heading indicator.

The second method for presenting nearest airport
information is within a moving-map display. In this
method, the nearest airports are shown directly on the
map display, with bearing and distance shown next to
the airport.

The third method for presenting nearest airport
information is a compromise between the first two
and is referred to as the “enhanced-text method.” This
method is the same as the text-only method, with the
exception of an orienting symbol added to each air-
port listing. This symbol provides a direct indication
of the relative direction of the airport, based on the
current aircraft heading and bearing to the airport.
The symbol was intended to provide the same kind of
relative direction information available from the map
display, but it is presented in a tabular format.

In addition to these three types of display formats,
another question of interest was how the use of a track-
up vs. anorth-up map display mightaffect the use ofeach
of the formats. A third variable that was manipulated was
the aircraft heading. This variable was included because
of prior research that indicated a need for mental rotation
that varied as a result of aircraft heading.

The final factor that was manipulated was the
subject group. One question of interest was whether
aircraft experience would have an effect on the ability
to orient under various conditions. A second question
was whether the presence and use of a heading indica-
tor during a trial would effect the ability to orient. To
answer both of these questions, three groups of par-
ticipants were used in the study. The first group of
participants was comprised of non-pilots, having no
flight experience. During the experiment, partici-
pants in this group interacted only with the GPS unit
and were not required to fly the simulator. A second
group of participants consisted of pilots holding at
least a private pilot certificate but like the first group,
interacting only with the GPS display. The final
group of participants included pilots holding at least
a private pilot certificate, and in addition to interact-
ing with the GPS display, also flew a flight simulator
during performance of the orientation task. The simu-
lator provided the pilot access to a heading indicator
that could be used to aid in orientation decisions.

METHODS

Participants

Thirty-six participants were recruited from the
Oklahoma City metroplex area. Twenty-four of the
participants held current private pilot certificates.
The other 12 participants were non-pilots. Pilots were
recruited from local fixed-base operations (FBOs).
Non-pilots were recruited through Acheson Consult-
ing, Incorporated, a firm contracted by the FAA to
provide experiment participants for Civil Aeromedi-
cal Institute research projects. All participants were
paid. Information was collected regarding participant’s
education level, gender, flight experience, age, hand-
edness, and GPS experience. Among the pilot partici-
pants, only one was female. Among the non-pilots,
four were female. Flight experience among the two
pilot groups was similar (860 average flight hours for
the non-simulator group, 757 average flight hours for
the simulator group). GPS use among the two pilot
groups was also similar with 6 of 12 from the non-
simulator group reporting having used a GPS and 7 of
12 from the simulator group reporting having had
experience with a GPS unit. None of the non-pilots

had ever used a GPS display.


DOT/FAA/AM-98/12

Office of Aviation Medicine
Washington, D.C. 20591

GPS Design Considerations:
Displaying Nearest Airport
Information

Kevin W. Williams

Civil Aeromedical Institute
Federal Aviation Administration
Oklahoma City, OK 73125

April 1998

Final Report

This document is available to the public
through the National Technical Information
Service, Springfield, Virginia 22161.

@

U.S. Department
of Transportation

Federal Aviation
Administration


Participants were asked to perform a five-step ori-
entation procedure. The first step was to note the
current aircraft heading. The second step was to press
the “NR” button on the display to bring up the nearest
airport information. Based on the information pre-
sented in the display, the third step was to decide the
relative direction of the nearest airport in the form of
clock position. That is, participants had to decide the
clock position that corresponded to the direction to
the nearest airport, with 12 o’clock being directly in
front of the aircraft and 6 o’clock directly behind the
aircraft. The fourth step was to press the direct-to
button (i.e., the button with the D with an arrow
through it) on the GPS display to bring up the screen
shown in Figure 2. The final step was to press the
point on the large black circle corresponding to the
appropriate clock position of the nearest airport (see
Figure 2). After the large circle was pressed, the trial
ended, and the next trial was immediately begun.

Nearest airport information was presented in one
of three ways. The first method, shown in Figure 3,
was called the text-only method. In this method, the
nearest airports were listed in a tabular format on the
screen with the airport identifier, bearing to the air-

port, and distance to the airport shown. An asterisk
was positioned next to the closest airport for easy
identification. In the example shown in Figure 3, the
aircraft is on a heading of 165 degrees. The nearest
airport, OKO9, is at a bearing of 212 degrees, or
approximately between the 1 and 2 o’clock position
(47 degrees to the right) from the aircraft heading.
The participant, after deciding the relative direction
of the nearest airport, would press the direct-to button
to bring up the display shown in Figure 2, and would
then press approximately the 1:30 position on the circle
to indicate the relative direction of the nearest airport.

The second method for presenting nearest airport
information is shown in Figure 4. Known as the
enhanced-text method, this method is similar to the
text-only method with the exception of an additional
symbol located to the right of the airport information.
This symbol is an indication of the relative direction
to each of the airports listed. In the example shown in
Figure 4, the aircraft is on a heading of 015 degrees.
Airport 3F7 is at a bearing of 135 degrees. The
orientation symbol on the right indicates that to fly
toward airport 3F7, the pilot needs to turn 120
degrees to the right, or to the 4 o’clock position. As

Figure 2. GPS display after pressing the direct-to button

6


experiment, presentation of trials was grouped by pre-
sentation mode (text, map, enhanced-text) within map
mode (track-up, north-up). Participants received a mini-
mum of ten practice trials on a particular presentation
mode and then were given four actual trials for that
mode. Within each set of four actual trials, the order of
northbound and southbound trials was random. During
the practice trials, participants were first presented with
at least five trials undera northbound condition and then
at least five trials for the southbound condition. The
number of practice trials for a particular mode was
extended if the sum of the orientation error over the last
two trials exceeded 160 degrees, indicating the partici-
pant was confused regarding the task procedure.

After completing the four actual trials for a particular
presentation mode, the participant was given practice
and actual trials for the next presentation mode. After all
modes had been completed under a particular map mode
condition, the map mode was changed (from track-up to
north-up or vice versa), and practice and actual trials
were given for each presentation mode as described
above, with the exception that only two practice trials
were given for each mode, unless the orientation error on
the last practice trial exceeded 80 degrees. In all, a
minimum of 36 practice trials were completed, along

with 24 actual trials. The order that participants re-
ceived presentation and map mode conditions was
counterbalanced.

Following completion of the experimental task, par-
ticipants were debriefed and asked which of the experi-
mental conditions they preferred the most. Their
preferences were recorded and they were then dismissed.

Orientation Task

Figure 1 shows an example of the GPS display
(north-up map mode) at the beginning of each trial.
Under the track-up map mode, the airplane symbol
pointed straight up and the current aircraft heading
was shown in the center box above the moving-map
display (in place of the large “N”). Participants flying
the simulator were asked to maintain the course shown
on the display. No airports were shown on the mov-
ing-map display until after the nearest airport func-
tion had been activated to prevent participants from
beginning the orientation task early. The actual orien-
tation task began when a large red “EMERGENCY”
message appeared just above the airplane symbol,
accompanied by a steady beeping from the computer
speaker which was the indication for the participant to
begin the orientation task.

Figure 1. Example GPS display at the beginning of each trial (north-up map mode)

5


information, we can hypothesize that a map-based
presentation would be superior because a map dis-
plays orientation information directly, while orienta-
tion must be mentally computed for a text-based
display by determining the difference between the
airport bearing and the current aircraft heading. The
need to integrate information from two separate sources
should be more difficult and should take longer than
when the information is already integrated, as is
found with a map-based presentation.

Despite the expected advantage of a map display
over text, there are several reasons for maintaining a
text-only display of nearest airport information. First,
not all GPS units have a moving-map display. It
would be unreasonable to require the added expense
of a moving map only for the purpose of displaying
nearest airport information, if the advantage gained
thereby was minimal. Second, a map display can be
more cluttered than a text display, leading to the
possibility that some information on the screen is
obscured. Finally, there are other reasons for display-
ing nearest airport information besides an in-flight
emergency. For these other tasks, the nearest airport
might not be as important as one further away. The
nearest airport function allows the user to access
information about an airport that might not presently
be visible on the map display.

In addition, while there are reasons to suspect that
amap display is superior to a text display for providing
orienting information, there are reasons to believe
that no advantage, or at least a minimal advantage,
exists. One reason is that pilots have experience con-
verting a given heading into a generalized compass
direction. If the pilot has a clear image of the aircraft’s
current heading, either by referencing the heading
indicator on the instrument panel, or noting the
heading from the GPS unit itself, then deciding the
relative bearing between the aircraft heading and any
given actual bearing should take very little time. A
second reason depends on the type of moving-map
display used. The two most common types of moving-
map displays are the north-up display and a track-up
display. In a north-up display, the aircraft symbol
rotates to indicate the current heading of the aircraft
relative to the top of the map, which indicates north.
In a track-up display, the aircraft symbol continu-
ously points straight up, while the map rotates. Thus,
the top of the map indicates the current aircraft heading.

The relative benefit ofa track-up versus a north-up
display is dependent on the type of task being per-
formed (Harwood & Wickens, 1991; Hooper & Coury,
1994; Wickens, 1992). Wickens (1992) hypothesized
that a track-up display would be superior to a north-
up display for performing an orienting task. Aretz
(1991) further hypothesized, and provided empirical
evidence to support, the idea that the need to perform
a mental rotation (Shepard and Metzler, 1971) caused
most of the delay when using a north-up map. Mental
rotation will take longer when the aircraft is on a
generally south-bound heading than when it is gener-
ally north-bound. It is possible that the delays caused
by a need to mentally rotate the map image could
eliminate the advantage ofa map display over the text-
based display. This would suggest that only a track-up
display would be superior to a text-based display when
the aircraft is on a generally south-bound heading.

Interestingly, the earlier discussion regarding the
ability of a pilot to convert a given bearing into a
direction (i.e., relative to north) presents an intrigu-
ing possibility. If the pilot has access to a moving map
prior to being presented the text-based orientation
information, then orienting should be quicker or
more precise if that map was a north-up map than if
it was a track-up map. The reason is that, with the
north-up map, only a single mental rotation is re-
quired to derive orientation information whereas,
with a track-up map, the pilot must first mentally
rotate the image to derive an absolute heading before
mentally rotating the image again to derive orienta-
tion information to the airport. For example, given an
airport bearing of 155 degrees and an aircraft heading
of 45 degrees, orientation to the airport is determined
by the angle between 45 and 155 degrees. Using a
north-up map, the aircraft symbol is already at the
proper angle for making this determination; however,
with a track-up map, the aircraft symbol is not in the
correct position but must first be mentally rotated to
45 degrees before determining orientation to the airport.

Before imposing a requirement for the graphical
presentation of nearest airport information in a GPS
display, it would be useful to test whether a measur-
able advantage is gained. Also, it might be possible to
gain the expected advantage of the map display if a
symbolic representation of orienting information can be
presented as part of the text display. By providing the
same amount of information in regards to orientation as




The purpose of this definition was to eliminate error
caused by an unsteady hand or by imprecision in the
touch-screen panel. This allowed us to focus on those
errors that were actually due to misjudging the relative
direction to the nearest airport. A 3x3x2x2 analysis of
variance was performed on the number of mis-
orientation errors committed by participants under
each experimental condition.

For all of the analyses reported in this paper, no
significant 3-way or 4-way interactions were found, so
for the sake of brevity, these will not be discussed.
Table 1 gives a count of the number of misorientation
errors for each experimental condition, with the ex-
ception that we have collapsed across aircraft heading,
since none of the significant effects involved this
factor. Looking at the results of the analysis, the 2-way
presentation mode x map mode interaction was sig-
nificant, F(2, 66) = 3.913, p = 0.025. Also, two main
effects were significant. The effect due to presentation
mode was significant, F(2, 66) = 13.258, p< 0.001, as
was the between subjects effect of participant type,
F(2, 33) = 6.212, p = 0.005.

Table 1. Misorientation error totals

From Table 1, it is clear that the significant effect
of participant type was because non-pilots made sig-
nificantly more errors than either of the pilot groups
(55 errors for the non-pilots vs. 20 and 27 errors for
each of the pilot groups). This was true under all
presentation modes but particularly for the text-only
condition. The text-only condition was clearly the
most difficult, with more than half of all of the errors
(62 of 102) made under this presentation mode.
Additionally, even if the non-pilots are eliminated
from consideration, more errors were made by pilots
in the text-only condition than in both of the other
conditions combined (28 vs. 19 errors respectively).

Figure 6 shows the interaction between presenta-
tion mode and map mode on the number of
misorientation errors. Note that the numbers used in
the figure are total misorientation errors across all
participants and not the number of errors per partici-
pant that was used in the actual analysis of variance.
The reason for the change is that these numbers are
easier to understand and display the same profile as
the errors per participant numbers. As can be seen

Map Presentation Participant Type
Mode Mode Pilots/NoSim Pilots/Sim Non-Pilots | Total
EText 1 3 5 9
North-Up Map 3 5 10 18
Text-Only 5 6 16 27
Total 9 14 31 54
EText 3 2 3 8
Track-Up Map 0 2 3 5
Text-Only 8 9 18 35
Total 1 13 24 48
x 35
27
[=  =Track-Up

—S— North-up

Map

Text

Figure 6. Number of misorientation errors as a function of presentation mode and map mode.

9


11000

10000

10651

aan

=  =Track-Up

| North-Up

Map

Text

Figure 7. Response time as a function of presentation mode and map mode

Table 3. Additional practice trials

Map Aircraft Presentation Mode

Mode Heading Etext Map Text-only Total
North 1 1 1 3

Track-Up South 1 2 15 18
Total 2 3 16 21

North 1 0 9 10

North-Up South 6 7 43 56
Total 7 7 52 66

Table 3 shows the total additional practice trials for
each experimental condition, with the exception that
we have collapsed across participant type, since none
of the significant effects involved this factor. Looking
at the results of the analysis, the main effects due to
map mode, F(1, 33) = 4.341, p = 0.045, presentation
mode, F(2, 66) = 8.18, p = 0.001, and aircraft head-
ing, F(1, 33) = 9.851, p = 0.004, were all significant.
In addition, the 2-way presentation mode x aircraft
heading interaction was significant, F(2, 66) = 3.612,
p= 0.032. No other main effects or interactions were
significant.

From Table 3, we see that significantly more addi-
tional practice was required for the text-only condi-
tion than for the other two conditions and that more
practice trials were required for the north-up map
mode than for the track-up map mode (66 vs. 21
additional trials respectively). Finally, significantly
more practice trials were required when the aircraft

11

was on a generally south heading than when it was
traveling generally north. While most of the addi-
tional practice occurred for the text-only condition,
one interesting note is the increased number of prac-
tice trials for both the enhanced-text and map condi-
tions when the map mode was north-up and the
aircraft heading was generally south. For both presen-
tation modes, the data suggests confusion about the
correspondence between the aircraft symbol heading
and the airplane heading. In the case of the map-mode
condition, participants would forget to mentally ro-
tate the image to the appropriate orientation. In the
case of the enhanced-text condition, participants were
sometimes confused about whether the orientation
symbol was relative to north or relative to the current
airplane heading. The existence of this confusion was
substantiated both by post-experimental questioning
of the participants and by remarks made during practice.


Technical Report Documentation Page

T. Report No. 2. Government Accession No. 3. Recipients Catalog No.
DOT/FAA/AM-98/12

4, Title and Subtille 5. Report Date

GPS Design Considerations: Displaying Nearest Airport Information April 1998

6. Performing Organization Code

7. Authors) B. Performing Organization Report No.
Williams, K.W.
9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

FAA Civil Aeromedical Institute
P.O. Box 25082

Oklahoma City, OK 73125 11. Contract or Grant No.

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered

FAA Office of Aviation Medicine
Federal Aviation Administration
800 Independence Avenue, SW.

Washington, DC 20591 14. Sponsoring Agency Code

15. Supplemental Notes

16. Abstract

Thirty-six participants were tested in a flight simulator on their ability to orient toward the nearest airport, based
on the manner in which information was presented on a global positioning system (GPS) display. Results
indicated that use of the tabular, text-only format normally found on such displays was significantly slower and
less accurate than either a map display of nearest airport information or a text display that included an
orientation symbol. In addition, it was found that pilots tended to ignore information available from the
heading indicator, and instead, focused solely on the GPS display to perform the task. Discussion of the results
includes the need to support pilot decision-making through interface design and the development of design
guidelines for GPS displays.

17. Key Words 18. Distribution Statement
Global Positioning System, Human-Computer Interface, | Document is available to the public through the
Aircraft Displays, Applied Psychology National Technical Information Service,
Springfield, Virginia 22161
79. Security Classif. (of this repor) 20. Security Classi. (of this page) 21. No. of Pages 22. Price
Unclassified Unclassified 18

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


NOTICE

This document is disseminated under the sponsorship of
the U.S. Department of Transportation in the interest of
information exchange. The United States Government
assumes no liability for the contents or use thereof.


Sel Arpt Brg Dist i
* OKO9 212 19.0
F641 159 23.7

Figure 3. Text-only method of presenting nearest airport information

Sel Arpt Brg Dist
H01 201 19.4 td
* 3F7 135 17.0 ¥

Figure 4. Enhanced-text method for presenting nearest airport information

7


from Figure 6, the significant interaction effect is due
primarily to there being more errors using the north-
up map for the map presentation condition, but more
errors using the track-up map when nearest airport
information was presented in the text-only format.
This last finding seems to support the hypothesis
stated earlier that an additional mental rotation is
required in the text-only condition when referencing
a track-up map. Map mode did not seem to have an
effect on the probability of making an error under the
enhanced-text condition.

Response Time

A 3x3x2x2 analysis of variance was performed on
the response time between presentation of nearest
airport information until the relative direction to the
nearest airport was indicated by touching the appro-
priate point on a circle drawn on the touch-screen
panel (see Figure 2). Response time was measured in
milliseconds.

Table 2 shows the mean response time for each
experimental condition, again with the exception that
we have collapsed across aircraft heading since none of
the significant effects involved this factor. Analysis of
these factors yielded significant effects due to map
mode, F(1, 33) = 7.468, p = 0.01, and presentation
mode, F(2, 66) = 42.922, p < 0.001, as well as the 2-
way presentation mode x map mode interaction, F(2,
66) = 4.982, p = 0.01. No other main effects or
interactions were significant.

Looking at Table 2, we see that participants per-
formed significantly slower while using the north-up
map mode than when using the track-up map mode
(7525 and 6811 milliseconds respectively). Unlike
the commitment of errors, non-pilots did not signifi-
cantly differ from the pilots in their response times.

Participants were nearly twice as slow at interpreting
the text-only presentation of nearest airport informa-
tion than they were interpreting either the enhanced-
text or map presentations (10573, 5451, and 5481
milliseconds respectively).

Figure 7 shows the interaction between presenta-
tion mode and map mode on response time. As can be
seen from Figure 7, the significant interaction effect is
due primarily to slower response times using the
north-up map for the map presentation and enhanced-
text conditions, but not for the text-only condition.
As could be expected, the largest difference in re-
sponse time was found for the map condition. While
the difference was not significant, the slightly longer
response times for the enhanced-text condition while
using the north-up map could be attributed to some
confusion regarding how to interpret the orientation
symbol. Some of the participants suggested after
completion of the experiment that they were confused
about whether the orientation symbol was relative to
north or relative to the current aircraft heading. This
confusion seemed more likely after being exposed to
a north-up map.

Practice Trials

One final analysis was performed on the number of
additional practice trials required for each of the
experimental conditions. According to the experi-
mental paradigm, participants received a minimum
number of practice trials for each of the experimental
conditions. Additional trials were administered if a
predetermined level of performance had not been
achieved. A 3x3x2x2 analysis of variance was per-
formed on the number of additional practice trials
required for each condition.

Table 2. Response time averages (in milliseconds)

Map Presentation Participant Type

Mode Mode Pilots/NoSim Pilots/Sim Non-Pilots | Mean
EText 7542 5344 4365 5750

North-Up Map 6823 6338 5835 6332
Text-Only 10579 9898 11007 10495

Mean 8314 7193 7069 7525

EText 7067 4301 4088 5152

Track-Up Map 4429 4427 5034 4630
Text-Only 10077 10159 11718 10651

Mean 7191 6296 6946 6811