A Usasitrry Survey of GPS Avionics EQuipMENT:
SOME PRELIMINARY FINDINGS

INTRODUCTION

The accelerated development and introduction of
Global Positioning System (GPS) receivers for use in
airborne navigation has outpaced the capacity of
international aviation authorities to fully implement
regulations and guidance for the safe and efficient use
of such devices (Nendick & St. George, 1996a).
Technical Standard Order (TSO) C129 Al is the
document currently used to cercify standalone, In-
strument Flight Rules (IFR) GPS receivers for instal-
Jation in the United States and Canada, and isaccepted
as the certification standard elsewhere, including
Australia and New Zealand. However, it appears to
have had little influence on standardizing receiver
architectures, interfaces, and operating manuals
(Heron, Krolak, & Coyle, 1997). Recent flight simu-
lation research performed at the Federal Aviation
Administration Civil Aeromedical Institute (FAA/
CAMI) illustrates that some features of GPS-receiver
interfaces can compro-aise their effective use and
perhaps undermine safety (Williams, 1998; Wreggit
& Marsh, 1998). Furthermore, FAA flight tests using
brand-name receivers have revealed several human
factors issues related to pilot interaction with receiver
interfaces (Williams, in press; Winter & Jackson,
1996). These reports underscore the need for GPS-
receiver standards that exceed the criteria specified in
TSO C129 Al. Human factors issues associated with
receiver architectures, interfaces, and operating manu-
als need to be specifically addressed.

At least two human factors references directly
support TSO C129 Al. McAnulty’s (1994) review of
human factors principles and guidelines for the de-
sign of controls and displays for standalone GPS and
Long Range Navigation (LORAN) receivers is ger-
mane to regulatory requirements. In addition, the
FAA has issued an aircraft certification human fac-
tors and operations checklist for standalone GPS
receivers (Huntley, Turner, Donovan, & Madigan,
1995). It includes both a bench and a flight test,
which were designed to assist certification personnel
and manufacturers in evaluating receiver interface
characteristics of GPS receivers to be certified in

accordance with TSO C129 Al. The bench test
assists in evaluations of GPS receivers that do not
require aircraft installation and a test flight. The
flight test helps in evaluating GPS-receiver design
characteristics and functions during actual flight
conditions. Both checklist tests focus on GPS-receiver
controls, displays, and operating characteristics. To-
gether with the guidelines proposed by McAnulty

- (1994), the checklist tests represent important progress

in resolving significant human factors issues associ-
ated with GPS receivers and their certification. How-
ever, evidence that considerable work remains on
these issues is manifest in requests from GPS manu-
facturer and certification personnel for guidance on
numerous human factors issues for which they have
no baseline data.

The research reported here is intended to comple-
ment existing human factors data by providing base-
fine measures of pilot perceptions of, and experiences
with, GPS receivers. This research is based on the
163-item GPS User Survey 97 (Nendick, 1997),
which was administered to 1,880 pilots in the United
States (US). Nendick (1994) administered an earlier
version of this survey to 227 New Zealand pilots and
js currently administering a farther-modified, 1998
version to 4,000 Australian and New Zealand pilots.
In the US, the survey represents the first systematic
attempt to quantify a large sample of pilot percep-
tions of GPS receivers. Together with the survey data
from New Zealand and that forthcoming from Aus-
tralia, the US data provide a unique source of infor-
mation that can be aggregated with existing human
factors data (e.g., usability tests) to properly support
the tasks of pilots, certification personnel, and GPS-
receiver manufacturers. One of the many challenges
for the FAA as it moves toward greater dependence on
GPS-based navigation is to supplement TSO C129
Al and future technical standard orders with human
factors specifications. These should ensure usability
through some basic standardization guidelines, with-
out prohibiting GPS-receiver manufacturers from
adding new features to their GPS devices.


This approach to identifying human factors issues
in certification has at least two advantages over the
current approach. The first advantage is that certifi-
cation personnel and manufacturers would collabo-
rate with human factors specialists in examining
issues and developing materials. Just as it is for GPS
receivers, end-user participation is critical for the
acceptance and use of certification test materials.
Second, standardization of tests, checklists, and other
certification material will go along way to ensure that
GPS receivers have standardized architectures, inter-
faces, and operating manuals. Current practices place
considerable onus on certification personnel to gather
information and develop their own supplemental
materials for certification tests. Consequently, subtle
variations in certification materials and procedures
impose greater demands on certification. personnel
and, perhaps, make the task of GPS-receiver stan-
dardization more difficult. Adopting a systematized
approach for developing human factors standards in
support of certification personnel and GPS manufac-
turers may ease this difficulty.

REFERENCES

Clarke, B. (1994). Aviator’s guide to GPS. New York,
NY: TAB Books.

Driskill, W.E, Weissmuller, JJ., Quebe, J.C., Hand,
D.K., & Hunter, D. (1997). The use of weather
information in aeronautical decision-making: II.
U.S. Department of Transportation, Federal Avia-
tion Administration, Office of Aviation Medi-
cine, Washington, DC. DOT/FAA/AM-97/23.
NTIS # ADA340406.

FAA (No date). AA Statistical Handbook of Aviation,
pp. 7-4/7-9. (Online). Available: <hrtp://
api. hq. faa.gov/handbook/1996/toc96.htm>
(1998, July 28).

Heron, R., Krolak, W. & Coyle, S. (1997). A human
factors 2pproach to the use of GPS receivers.
Vancouver, BC: Heren Ergonomics, Incorporated.

Hundey, Jr., M.S., Turner, J.W., Donovan, C.S., &
Madigan, E. (1995). FAA aircraft certification
human. factors and operations checklist for
standalone GPS receivers (TSO C129 Class A).
Technical Report DOT/FAA/AAR-95/03. Wash-
ington, DC: Federal Aviation Administration.

McAnulty, D.M. (1994). Guidelines for the design of
GPS and LORAN receiver controls and displays.
Technical Report DOT/FAA/RD-95/01. Wash-
ingron, DC: Federal Aviation Administration.

Nendick, M.D. (1994). Global Positioning Sys-
tem (GPS): Human factors aspects for gen-
eral aviation pilots. Unpublished masters
thesis. Palmerston North, New Zealand:
Massey University.

Nendick, M.D. (1997). GPS User Survey 97, Callaghan,
NSW, Australia: The University of Newcastle.

Nendick, M.D. & St. George, R. (1996a). General
aviation pilots and GPS: Some results from a New
Zealand study. Airways, 9, 12-6.

Nendick, M.D. & St. George, R. (1996b). Human
factors aspects of global positioning systems (GPS)
equipment A study with New Zealand pilots. In
R. Jensen (Ed.) Proceedings of the Eighth Inter-
national Symposium on Aviation Psychology, pp.
152-7. Columbus, OH: The Ohio State University.

Williems, K.W. (1998). GPS design considerations:
Displaying nearest airport information. U.S. De-
partment of Transportation, Federal Aviation
Administration, Office of Aviation Medicine,
‘Washington, D.C. DOT/FAA/AM-98/12. NTIS
# ADA346043.

Williams, K-W. (in press). GPS user-interface design
problems. U.S. Department of Transportation,
Federal Aviation Administration, Office of Avia-
tion Medicine, Washington, D.C.

Winter, S. 8& Jackson, S. (1996). GPS issues. Technical
Report DOT/FAA/AFS450. Oklahoma City, OK:
Federal Aviation Administration.

‘Wreggit, S. & Marsh Ill, D. (1998). Cockpit integra-
tion of GPS: Initial assessment- menu, formats
and procedures, U.S. Department of Transporta-
tion, Federal Aviation Administration, Office of
Aviation Medicine, Washington, D.C. DOT/
FAA/AM-98/09. NTIS # ADA341122.


item alphas indicate that pilot ratings for most of the
survey topic areas were reliable: Receiver Controls
and Displays (.92), Operating Logic (.90), Receiver
Functions (.89), Receiver Operations (.91), Gperat-
ing Procedures (.60), Navigation Performance (.70),
Pilot Attitudes (.81), and Training (.56). The rela-
tively low reliability estimates for Operating Proce-
dures and Training may be due to the smaller number
of items in these topic areas and the large variety of GPS
receivers, each of which has different operating manual.

Underlying factor structures were extracted by
entering pilot ratings from each of the survey topic
areas into separate exploratory principal components
factor analyses that utilized varimax rotation to ob-
tain factor solutions. A multivariate analysis of vari-
ance (MANOVA) was then utilized to determine if
differences in mean factor ratings were a function of
FAA region (AAL and ASW), GPS experience (below
the 50* percentile and above the 50" percentile), and
GPS-receiver type (hand-held and panel-mount).
Pilots with 200 hours or less ranked below the 50°
percentile for GPS experience, whereas pilots with
more than 200 hours ranked above the 50TM percentile.

Pilot ratings were pooled across FAA region after
preliminary analyses revealed differences that were
attributable solely to the availability of ground-based
navigational aids within each region. For example,
regions located in the contiguous US have more very
high frequency, omni-directional range (VOR) navi-
gational aids than the AAL Region. Consequently,
pilots in the AAL Region were less likely to usea VOR
navigational aid as a backup to GPS than were pilots
in the ASW Region. Pilots in the AAL Region also
were less likely to use a backup means of navigation
because this region has fewer navigational aids than
do regions located in the contiguous US. Hence, the
following results are based on the exploratory factor
analyses of each survey topic area and the MANOVA,
which included GPS experience and GPS-receiver
type as independent variables, and mean factor rat-
ings within each survey topic area as dependent
variables.

Receiver Controls and Displays
Consistent with the findings of Nendick (1994),
the following four factors emerged from the factor
analysis of this topic area.
¢ Control Dimensions (button and/or knob opera-
tion, labeling, and layout)

* Accessories and Installation (power supply, an-
tenna, receiver size and shape, fit into aircraft)
*Display Readability (readability of symbols and

day/night illumination)
Display Messages (warning indications)

Generally, higher ratings on these factors indicate
a favorable view of the particular receiver that was
rated. MANOVA tests of pilot ratings revealed that
the main effect of GPS-receiver type was significant
for both the Accessories and Installation and the
Display Readability factors. Relative to hand-held
receivers (M=5.6, SD=1.0), the accessories and in-
stallation associated with panel-mount receivers
(M=6.0, SD=0.8) were assigned significantly higher

_fatings by pilots [F(1,184)=6.8, p<.01]. Panel-mount

receivers (M=5.4, SD=1.1) also received significandy
higher ratings on the Display Readability factor than
did hand-held receivers [M=6.0, SD=1.0;
F(1,184)=1 1.2, p<.01). Despite these differences, all
pilots gave fairly high ratings to the four factors that
characterized receiver controls and displays.

Operating Logic
Two factors emerged from the factor analysis of
this topic area.
* Programming Demands (route programming and
review, waypoint entry, standardization)
* Cognitive Demands (practice required for profi-
ciency, reliance on memory, operating complexity)

None of the interaction and main effect tests
involving these factors was significant.

Receiver Functions
Two factors emerged from the factor analysis of
this survey topic area.
“Navigation Feedback (desired track, distance to
go, crosstzack error and CDI, and groundspeed)
Receiver Integrity and Emergency Information
(RAIM warning, satellite status, nearest airport,
and present position)

None of the interaction and main effect tests
involving these factors was significant.

Receiver Operations
Two factors emerged from the factor analysis of
this survey topic area.


METHOD

Administration ofthe GPS User Survey was partof
a larger effort to explore free-flight enabling tech-
nologies, like GPS, and their impact on pilot perfor-
mance of tasks related to communication, navigation,
and surveillance functions. During the course of its
modification for use in the US, the original 125-item
survey developed by Nendick (1994) was expanded
to include 163 questions. These questions were cat-
egorized into the following topic areas: Receiver
Controls and Displays, Operating Logic, Receiver
Functions, Receiver Operations, Operating Proce-
dures, Navigation Performance, Pilot Aititudes, and
Training. Seven-point, Likert-type rating scales were
used to measure pilots’ responses to survey questions.
Several open-ended questions were included within
the survey to gather qualitative data on particular
issues that could not be addressed using the question
and rating format. Finally, several demographic ques-
tions were inserted to determine the extent to which
the sample of pilots used in this research represented
the General Aviation (GA) pilot population.

The 35-minute survey was administered to pilots
in two different FAA Regions. Pilots had to have a
current medical certificate, be at least a private pilot,
and have a minimum of five hours of GPS flight time
to be eligible for participation in the survey. Eighty-
eight pilots from the FAA Southwest Region (ASW)
completed the survey at FAA/CAMI in December
1997. These pilots were part of a group of 150 pilots
who participated in several research studies during a
one-day session at FAA/CAMI. Thus, nearly 59% of
the pilots in the ASW Region sample completed the
survey. In April 1998, the survey was mailed to 1,800

FAA Alaskan Region (AAL) pilots, of which approxi-
mately 12% (N=220) completed it. This low return
rate is consistent with that obtained for other surveys
of AAL Region pilots (e.g., see Driskill, Weissmuller,
Quebe, Hand, & Hunter, 1997).

The average age of pilots in the AAL and ASW
Regions was 49 (SD=10) and 41 (SD=14), respec-
tively. Table 1 shows the average, median, and stan-
dard deviation for rotal hours and GPS experience (in
hours) for each pilot sample. Pilots from both regions
were comparable in total hours. A comparison of
GPS experience revealed that AAL Region pilots had
nearly twice as many GPS hours than pilots in the
ASW Region. The 50" percentile for GPS experience
was 200 hours.

Table 2 compares the actual distribution of fi-
censes within each region (see 1996 FAA Statistical
Handbook of Aviation) with the distribution ob-
tained for AAL and ASW Region samples. Observed
percentages for each region sum to less than 100%
because a small percentage of pilots did not indicate
which license they held. Although the AAL Region
sample is skewed more heavily, analysis of the license
distribution in both regions indicates that private
pilots comprised a very large majority of all survey
respondents. Given the skewed distribution and low
return rate, the results reported in the next section
would be most representative of GA pilots who hold
a private pilot license.

RESULTS

Estimates of internal consistency (i.e., coefficient
alpha) were calculated for each of the eight survey
topic areas. In general, the following standardized

Table 1. Demographics for Pilot Samples

FAA N Total Hours. GPS Hours
| Region Mean | Med Mean | Med | SD
AAL 220 1883 988 | 2919 414 240 621
ASW. 88] 1999) 957 | 2887 210 40 448
Both | 308/ 1917| 983 / 2905 354 | 200 582
Table 2. Pilot License as a Function of Region
FAA License Type (Actual and Observed in %)
Region Private Commercial Air Transport
Act. | Obs. | Act. | Obs. | Act. | Obs.
AAL 49.7 89.1 29.2 1.8 21.1 5.0
ASW 46.0| 37.5] 259; 386] 284 19.3



Training

Two factors emerged from the factor analysis of

this survey topic area.

*Knowledge and Experience Required (technical
training, and knowledge level and human factors
training needed)

Knowledge and Experience Attained (user knowl-
edge, training received, and user manual)

The main effect of GPS-receiver type was signifi-
cant for the Knowledge and Experience Required
factor [F(1,184)=10.1, p<.01]. Pilots assigned higher
ratings to panel-mount receivers (M=4.5, SD=1.0)
than they did to hand-held receivers (M=4.0,SD=1.1).
This finding indicates pilots perceive that panel-
mount receivers require more training to operate
proficiently. Finally, the main effect test of GPS
experience for the Knowledge and Experience At-
tained factor approached the nominal significance
level criterion of .05 [F(1,184)=3.0, p<.09}. Pilots
with more GPS experience assigned higher ratings
(M=4.4, SD=1.1) than did: pilots with less GPS
experience (M=4.2, SD=1.0), although this differ-
ence is not statistically significant.

DISCUSSION

The present research, which is based on a limited
survey, has produced several meaningful results. First,
MANOVA tests indicated thae: GPS experience and
GPS-receiver type did not interact to affect pilot factor
ratings within each of the survey topic areas. Thus, the
following discussion assumes that GPS experience and
receiver type combine in an additive fashion to influ-
ence pilot perceptions of GPS receivers. Significant
differences in pilot ratings as a function of GPS-receiver

type suggested that panel-mount receivers were better
ten hand-held rec“ =rs on factors such as display
readability, power supply, antenna, size and shape, and
fir into aircraft. Pilot ratings also revealed that panel-
mount receivers require more knowledge and training
to operate proficiently. This finding was not statistically
significant, although it is of practical importance. So,
too, is the statistically non-significant finding that pilots
who used panel-mount receivers rated themselves as
more complacent and reliant on GPS than pilots who
used hand-held receivers. In part, this finding may be
because panel-mount receivers provide continuous
monitoring of GPS signal integrity, whereas hand-held
receivers do not.

Significant differences in pilot ratings as a result of
GPS experience were distributed across several survey
topic areas. Pilot ratings suggested that, with more
experience, in-flight operation of GPS receivers be-
came easier, fewer operational errors were made,
course tracking improved, there were gains in know!-
edge of the receiver, and increased confidence in
using basic and complex functions. One possible
negative consequence associated with more GPS ex-
perience is that pilots perceive themselves to be more
relianton GPS and more complacent than pilots with
less experience.

Consistent with ratings of the New Zealand pilots
surveyed by Nendick (1994), the results.reported
here provide evidence of a discrepancy between pilot
ratings of GPS-receiver design and pilot performance

“in GPS-receiver evaluations (e.g., see Wreggit &

Marsh, 1998). A plausible explanation for this dis-
crepancy is presented by Clarke (1994) and Nendick
and St. George (1996b), who have warned of the
pitfalls related to pilot perceptions of the operational
simplicity of GPS. On one hand, pilots may be
captivated by the inherent simplicity and minimal
training required to execute frequently used basic
receiver functions. On the other hand, as Winter and
Jackson (1995) have demonstrated, pilots who have
not acquired a significant amount of knowledge and
training can become overwhelmed when they go
beyond basic receiver functions to complex ones that
are required for difficult navigational tasks. Examples
of subtle human factors issues associated with com-
plex receiver functions will likely be revealed during
flight tests using GPS Wide Area Augmentation
System (WAAS) terminal approaches and in future
tests of other difficult navigational tasks.

Another meaningful finding resulted from the
exploratory factor analysis of each survey topic area.
Separate sets of factors were identified that could be
used as a basis for supplementing existing certifica-
tion guidelines for GPS receivers. In combination,
certification personnel, manufacturers, and human
factors specialists could examine the specific factors
within each topic area for design issues relevant to
certification. Such an effort would result in coverage
of zraditional human factors issues related to receiver
displays and controls, as well as other topical issues,
such as those related to operating procedures, naviga-
tion performance, and training.


DOT/EAA/AM-99/9

Office of Aviation Medicine
Washington, D.C. 20591

A Usability Survey of GPS
Avionics Equipment:
Some Preliminary Findings

Kurt M. Joseph

Civil Aeromedical Institute
Federal Aviation Administration
Oklahoma City, Oklahoma 73125
Dieter W. Jahns

SynezTech Associates

Bellingham, Washington 98227 -
Michael D. Nendick

The University of Newcastle
Callaghan, NSW 2308, Australia
Ross St. George

New Zealand Civil Aviation Authority
Lower Hutt, New Zealand

000 £70666)

March 1999

Final Report

This document is available to the public

through the National Technical information

Service, Springfield, Virginia 22161.

U.S, Department

of Transportation ‘preo.quatrry mapzcren 2

Federal Aviation
Administration



eIn-flight Operation (one-handed operation, use
in turbulence, and night and day use)

Data Entry and Modification (creating and modi-
fying route, pre-flight and in-flight data entry,
undoing errors)

In general, higher ratings on these factors indicate
a favorable impression of the particular receiver that
was rated. There was a significant effect of GPS
experience for the In-flight Operation factor
{F(1,184)=4.0, p<.05]. Pilots with more GPS experi-
ence assigned significantly higher ratings (M=5.7,
$D=1.1) for in-flight operation of receivers than
pilots with less GPS experience (M«=5.3, SD=1.1).
Once again, th: overall ratings for these factors were
fairly high.

Operating Procedures
Four factors emerged from the factor analysis of
this survey topic area.
*Validation of Receiver Data (in-flight cross-checks
of information using other data sources)
*Operational Errors (incorrect data input, mis-
reading the display, and mode errors)
Navigation Contingencies (navigation backups for
GPS, use of other navigational methods with GPS)
eIncidents (incidents resulting from misréading
the display or incorrect input of data}

A significant main effect test for the Operational
Errors factor revealed that the amount of GPS expe-
rience influenced pilot ratings [F(1,184)=5.0, p<.03].
Pilots with less GPS experience assigned significantly
higher ratings (M=2.8, SD=1.0) for this factor than
did pilots with more GPS experience (M=2.5,
SD=1.0). This effect suggests that pilots with less
experience report that they make more errors during
their interaction with GPS receivers.

Navigation Performance
Four factors emerged from the factor analysis of
this survey topic area.
Awareness Issues (changes in situation awareness,
lookout, and instrument scan)
*Workload Issues (changes in mental and physical
workload, head-down time, and chart use)
*Course Tracking (tracking direct and to waypoints,
and accuracy of tracking)

*Decision Making (navigation decisions, flying in
marginal conditions, and flying near controlled
airspace)

The main effect of GPS experience was significant
for the Course Tracking factor [F(1,184)=4.8, p<.03].
Pilots with more GPS experience assigned signifi-
cantly higher ratings (M=5.9, SD=0.9) for this factor
than did pilots with less GPS experience (M=5.5,
SD=1.0). This finding suggests that pilots perceive
improvements in GPS course tracking as concomi-
tant with gains in GPS experience.

Pilot Attitudes
Four factors emerged from the factor analysis of
this survey topic area. The first two factors are consis-
tent with the findings of Nendick (1994).
*Confidence in GPS (use for IFR navigation and
non-precision approaches, and accuracy and reli-
ability of GPS device)
User Confidence (use of basic and complex GPS
functions)
*Dependence on GPS (complacency, reliance on
GPS for VFR and IFR)
*Use of Database (affordability and use of current
data)

The main effect of GPS experience was significant
for the User Confidence and Dependence on GPS
factors. [F(1,184)=5.6, p<.02; F(1,184)=4.5, p<.04,
respectively]. Pilots with more GPS experience as-
signed significantly higher ratings (M=6.0, SD=0.8)
for the User Confidence factor than did pilots with
less GPS experience (M=5.6, SD=1.0). The average
ratings for this factor were very high. Compared with
those who had less experience (M=3.9, SD=1.2),
pilots with more experience also assigned signifi-
cantly higher ratings (M=4.3, SD=1.3) for the De-
pendence on GPS factor. Overall, the ratings indicated
that pilots reported increased dependence on GPS as
they gain more experience with it. The main effect test
of GPS-receiver type for the Dependence on GPS factor
approached the nominal significance level criterion of
05 [F(1,184)=2.9, p<.09]. Pilots assigned higher rat-
ings to panel-mount receivers (M=4.4, SD=1.2) than
they did to hand-held receivers (M=3.9, SD=1.2), al-
though this difference is not statistically significant.


ACKNOWLEDGMENTS

The authors gratefully acknowledge the voluntary participation of the 308 pilots who com-
pleted survey forms. Thanks also to Ms. Tara Bergsten, Ms. Janine King, and Ms. Debbie Perry,
of OMNI Corporation, for their support during survey distribution, and Dr. David Hunter, FAA
Office of Aviation Medicine, for his administrative support of the survey. Finally, the authors
appreciate the assistance of Mr. John Hallinan, FAA Alaskan Region Flight 2000 Program
Manager, who organized survey-related activities in Alaska.

iii


Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3, Recipients Catalog No.
DOT/FAA/AM-99/9
2. Tite ond Subtitie &. Report Date
A Usability Survey of GPS Avionics Equipment: Some Preliminary April 1999
Findings
©. Performing Organization Code

7, Author(s) 8. Performing Organization Report No.
Joseph, K.M.", Jahns, D.W2, Nendick, M.D.’, and St. George, R.‘
9. Performing Organization Nome and Address 10. Work Unit No. (IRAIS)
‘BAA Civil Aeromedical Institute | "The University of Newcastle
*SynerTech Associates ‘New Zealand Civil Aviation Ti. Contract or Grant No.

| Authority
12. Sponsoring Agency name and Address 13. Type of Report and Period Covered
Office of Aviation Medicine

Federal Aviation Administration
800 Independence Ave., S.W.
Washington, DC 20591 ¥4, Sponsoring Agency Code

18. Supplemental Notes

16. Abstract

The rapid introduction of Global Positioning System (GPS) receivers for airborne navigation has outpaced the
capacity of international aviation authorities to resolve human factors issues that concern safe and efficient use of
such devices. Current certification technical standards appear to have had little influence on standardizing
receiver architectures, interfaces, and operating manuals—despite evidence from research simulation and flight
tests chat lack of standardization may undermine safety. The present research used factor-analytic techniques to
reduce 308 pilots’ ratings from a 163-item survey to 24 factors. These factors are suitable for identifying human
factors issues related to GPS receiver displays and controls, operating procedures, navigation performance,
training, and other topical areas. Multivariate analysis of variance revealed that GPS experience and receiver type
influenced pilot ratings for several of these factors. The results of this limited survey are consistent with previous
research, and their application to certification procedures and standards is discussed.

17. Key Words 18, Distribution Statement

GPS, Certification, Human Factors, TSO C129 Al, Document is available to the public through the
Pilot Experience, General Aviation, Aviation Safety National Technical Information Service
Springfield, Virginia 22161

19. Security Classif. (of this report) 20. Security Classi. (of this page) 21. No. of Pages 2. Price

Unclassified Unclassified : 10
Form DOT F 1700.7 (3-72) Reproduction of completed page authorized



NOTICE

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