DOT/FAA/AM-99/26 GpS User-Interface

Office ofAviation Medicine y-^ . Tfc 1 1 TT

Washington, D.c. 20591 JJesign Problems: II

Kevin W.Williams

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, Oklahoma 73125

November 1999

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 19991126 085

DTIC QUALITY INJECTED 4
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 thereof.
Technical Report Documentation Page

1. Report No.

DOT/FAA/AM-99/26

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

GPS User-Interface Design Problems

5. Report Date

November, 1999

6. Performing Organization Code

7. Author(s)

Williams, K.W.

8. Performing Organization Report No.

9. Performing Organization Name and Address

FAA Civil Aeromedical Institute

P.O. Box 25082

Oklahoma City, OK 73125

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency name and Address

FAA Office ofAviation Medicine

Federal Aviation Administration

800 Independence Avenue, SW.

Washington, DC 20591

13. Type of Report and Period Covered

14. Sponsoring Agency Code

15. Supplemental Notes

16. Abstract

This paper is the second of two of a review of human factors problems associated with the user-interface

design of a set ofGlobal Positioning System (GPS) receivers, certified for use in aircraft for instrument nonprecision approaches. Both papers focus on design problems associated with the interfaces and specific

inconsistencies across the set of interfaces that could cause confusion or errors during operation. Some

specific problems addressed involve the placement of units in the cockpit; the use and design of moving-map

displays; and problems associated with changes in course direction indicator sensitivity. Recommendations

for solving some of the problems are provided, as well as suggestions to the FAA, GPS manufacturers, and

pilots regarding the future development and use ofthese products.

17. Keywords

Global Positioning System, Human-Computer

Interface, Aircraft Displays, Applied Psychology

18. Distribution Statement

Document is available to the public

through the National Technical

Information Service, Springfield,

Virginia 22161

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

11

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
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 Steve Jackson and Steve Winter ofthe FAA's Technical

Programs Division, Flight Procedure Standards Branch (AFS-420) for their invaluable assistance in

providing information about the many GPS products currently on the market.
GPS USER-INTERFACE DESIGN PROBLEMS: II

ABSTRACT

Several Global Positioning System (GPS) receivers

were reviewed and human factors problems associated

with the user interface were noted. The problems documented belowinclude specific control and display problems, design inconsistencies across units, and general

design problems that apply to all ofthe units reviewed.

Discussing these problems highlights the need to make

pilots aware ofissues that may require specific training

or other preventive measures. Recommendations for

design improvements are provided.

INTRODUCTION

This paper is the second in a series of papers that

review human factors problems associated with the

user-interface design of a set of Global Positioning

System (GPS) receivers, certified for use in aircraft

for instrument non-precision approaches. No GPS

products are mentioned by name, since the aim ofthe

paper is not to criticize a particular GPS manufacturer. Instead, the paper focuses on design problems

and how these problems affect the pilot.

Data Collection

Most of the human factors problems reported in

this paper were obtained from interviews with subject

matter experts from the Federal Aviation Administration's (FAA's) Technical Programs Division,

Flight Procedure Standards Branch (AFS-420). Additionally, data were collected from an FAA technical

report (Winter & Jackson, 1996), as well as through

FAA internal memoranda (i.e., personal communications, S. Jackson, August, 1997; S. Jackson, February

18, 1998; S. Jackson, May 22, 1998, S. Winter,

September 25, 1996). Some information was gathered from theAeronautical Information Manual (FAA,

1998). Finally, data were taken from observation logs

of a recently conducted operational test of a GPS

Wide AreaAugmentation System (WAAS), and from

personal observation from the WAAS test.

Problems Previously Covered

In the first paper ofthis series (Williams, 1999a),

several human factors problems related to GPS receiver design and use were reported. These problems

included the overall complexity of operating a GPS

receiver, lack of adequate feedback for some button

activations, the lack of an "undo" function, and the

poor placement of buttons on the interface ofsome

receivers. Knob issues discussed included a lack of

feedback regarding the position of knobs and the

inability ofsome receivers to "wrap around" from A

back to Z when inputting alphanumeric information. Labeling problems that were discussed included

variations in the annunciator panels from unit to

unit, particularly in regard to the function for suspending automatic sequencing of waypoints in the

approach route. A second problem noted with the

annunciator panels was a lack ofco-locating the panel

with the GPS unit or with the navigational instrument used during an instrument approach.

Button labeling was also discussed. There is a

general lack of uniformity across units in regard to

the number, position, and labeling of buttons. In

addition, most units have one or two ganged knobs.

Function activation accomplished through knob turns

in one unit might be accomplished by button activations in a second unit.

Procedural problems with the units were also covered, including workload associated with the selection of an alternate airport, issues associated with

automatic vs. manual waypoint sequencing, and the

inconsistent functionality of the equipment being

driven by the GPS unit, such as the horizontal situation indicator and instrument landing system display. The functionality of these devices is highly

dependent upon the manner in which they are installed in the aircraft and can be different from

aircraft to aircraft, even though the GPS unit is the

same. For details of these problems and suggestions

for dealing with them, see Williams (1999a).
Design Problems

As in the original paper (Williams, 1999a), the

following design problems are not intended to be an

exhaustive list. In fact, many problems were not

included because of time and space constraints or

because they had been discussed in the previous

paper. Nor are the problems presented in any particular order of importance since the importance of a

specific problem cannot usually be determined without looking at how often it occurs and its effect on

pilot workload and performance. Further research is

required to make these determinations.

Unit Positioning

Because the GPS unit is an add-on device in most

cockpits, the location of the unit is limited by the

instrumentation already in place. In many instances,

this leads to the suboptimal placement of the unit.

Frequently, the unit is placed farther away from the

pilot than it should be, leading to difficulty in reading the display and in manipulating the controls.

Consequently, before approving a particular installation, the pilot should determine beforehand if the

unit will be too far away for proper use.

A second problem with unit positioning occurs

when the GPS unit is placed in the center console

between the pilot and co-pilot seats. The Instrument

Flying Handbook (FAA, 1980), in a discussion of

spatial disorientation, gives a method for purposely

inducing spatial disorientation in a student pilot for

training purposes. It states, "The instructor starts a

positive, coordinated roll toward a 30° or 40° angle of

bank. As this is in progress, the student (initially with

eyes closed) should tilt the head forward, look to the

right or left, then immediately return the head to an

upright position. The instructor should so time the

maneuver that the roll is stopped just as the student

returns the head upright. An intense disorientation is

usually produced by this maneuver..." (p. 11, italics

added). The manual continues with actions to prevent spatial disorientation including the following,

"Avoid sudden head movements, particularly during

takeoffs, turns, and approaches to landing" (p. 11).

By locating the GPS unit in the center console, the

pilot is forced to move his or her head down then back

up. This movement will likely occur during approaches and could also occur during turns. Positioning a GPS unitin this location would resultin a direct

conflict with the instructions for avoiding spatial

disorientation.

Display Problems

Multiple Pieces of Information. Often, several

different pieces ofinformation are co-located on the

GPS display. Because these displays are relatively

small, the information cannot be widely separated.

This can lead to confusion while reading the display.

Winter and Jackson (1996) reported the results of

flight-testing two separate GPS displays at the FAA

Technical Center in Atlantic City, NJ, and at the

University ofOklahoma in Norman, OK. They noted

that "A common mistake on the ... receiver was for

the subject pilots to dial in the ground speed value,

instead of the desired track, into the CDI course

window" (p. 4).

Moving-Map Displays. The presence of a moving-map display can greatly increase a pilot's situational awareness and has been shown to greatly

improve pilot decision-aiding (Aretz, 1991; Hofer &

Wickens, 1997; Williams, 1999b). However, there

have been some human factors-related problems noted

with moving map displays. One problem relates to

the small screen size of most units. Because these

units must be installed in the panel to be certified for

instrument approach use, manufacturers have been

constrained by how much room they have available.

While newer receivers are larger, many of the older

text displays have room for only 1 or 2 lines oftext.

Trying to place a moving-map display on these units

can lead to a very small and crowded display. Figure

1 shows an example of a moving-map display from

one of the larger display units on the market.

Figure 1: Example of a moving-map display

Looking at the figure, note the amount ofoverlap

of symbols. Of course, the display has options for

adjusting the amount and type of symbols that are

displayed, whether identifiers are included in the

display, and the scale ofthe map. However, if a pilot
has a need for displaying these options (such as

airport identifiers), then a certain amount of clutter

is inevitable simply because of the small screen size.

Notsurprising then, when two airports are in close

proximity, and they have similar identifiers (e.g., F28

and F29 identify two Oklahoma airports less than 10

miles apart), pilots can become confused as to which

airport they are viewing on the map display. This is

especially likely when the map is being used in an

other-than-north-up mode, where the orientation of

the two airports can change depending on the direction of travel of the airplane. In most of the units

reviewed that had a moving map, there was no immediate indication on the display of the selected map

mode (i.e., track-up, north-up, etc.). Verification of

the map mode required leaving the map display and

going to a page where the display characteristics are

selected. If the pilot is using the map for strategic

planning (e.g., deciding on an airport at which to

land in the presence ofsevere weather), it is vital that

the pilot realize the orientation of the map that is

being used.

One final problem that has been noted with moving-map displays is the tendency for some pilots to

try to use the map for real-time course guidance

(Steve Jackson, personal communication, January,

1999). Given a course line that is essentially 1 mile

wide, and a plane symbol that is 5 miles wide, the use

of the display for real-time course guidance is problematic, since the display does not provide enough

resolution to ensure accurate course following. During the approach, the problem is even more critical.

Furthermore, anything that tends to focus the attention ofthe pilot inside the cockpit is problematic, as

previousstudies have shown (Williams, 1998; Wreggit

& Marsh, 1998). One possible way to address this

issue would be to ask GPS manufacturers to include

a warning in their documentation regarding the inaccuracies of the moving map display.

CDI Sensitivity. One final display problem to be

discussed concerns the sensitivity ofthe course direction indicator (CDI). During an approach, the CDI

gives an indication ofthe plane's horizontal position

relative to the intended approach course. The CDI

can be either depicted directly on the GPS display, or

the unit can be controlling a separate CDI such as is

present in an instrument landing system (ILS) display. For current ILS systems, the signal diverges

continuously from the point oforigin, as is depicted

in Figure 2. For these systems, the sensitivity of the

CDI increases continuously as the airplane approaches

the signal source.

CDI sensitivity

changes as a

function of

distance from

origin.

Figure 2: CDI sensitivity for current ILS systems

0.3 mi.

Figure 3: CDI sensitivity for GPS systems

For the panel mounted GPS unit, CDI sensitivity

is controlled programatically by the unit itself. In the

en route mode, the CDI sensitivity is set at 5 miles.

Beginning at 30 miles from the final approach fix

(FAF), the CDI sensitivity is reduced to 1 mile.

When the airplane is 2 miles from the FAF, CDI

sensitivity is ramped down from 1 mile until it

reaches 0.3 miles at the FAF. This situation is depicted in Figure 3.

Consider the situation in which the airplane is

slightly offset (e.g., 0.1 mile to the right), but parallel

to the programmed course. For non-GPS-driven displays, the CDI would drift slowly to the right, from

the point at which the navigation signal was first
received. Small corrections by the pilot would maintain the airplane's course closer and closer to the

programmed course. On the other hand, for a GPSdriven display, the CDI would remain slightly offset,

but unmoving, beginning at 30 miles from the FAF.

It would remain still until, at 2 miles from the FAF,

the indicator would begin to move out as the sensitivity was ramped down from 1 mile to 0.3 miles.

Observation of pilots who have encountered this

situation has shown that, ifthey do not realize that a

change in CDI sensitivity is occurring, they conclude

that their heading has changed and that they have

started to drift off course (Steve Jackson, personal

communication, January 1999). Corrections for this

"course drift" have sometimes been quite drastic.

There is a light on the annunciator panel and usually

a change in the receiver display that indicates the

approach is active. When this light turns on, it

indicates that the unit has begun to ramp down the

CDI sensitivity from 1 mile to 0.3 miles. However,

pilots are not told explicitly that the sensitivity is

changing in all receivers. They must simply know

that this occurs at a certain point in time as indicated

by the annunciator light. An explicit indication of

CDI sensitivity would be better and would lead to

less pilot confusion.

Miscellaneous Problems

Button Label/Function Mismatch. Functions are

sometimes assigned to buttons in such a way that the

label on the button has no relevance to the function

it performs. This occurs because ofthe large number

offunctions that are performed with the unit, compared with the relatively small number of controls

(buttons, knobs, etc.) for performing those functions. One example of this is a unit that uses the

direct-to button for selection and de-selection ofthe

autosequencing mode (S. Winter, personal communication, September 25, 1996). One solution to this

mismatch is to have programmable button labels,

similar to those seen on multifunction displays found

in military aircraft. These buttons are co-located next

to the display, with the button function presented

above or to the side ofthe button on the display. The

same button can then be used for several functions,

while the function name changes on the display.

A similar problem occurs when two buttons on the

unit have intuitively equivalent labels. For example,

at least one of the units on the market has a button

labeled "select" and another labeled "enter." For

many units, as well as for other computer applications, the "enter" button is used to make a selection.

Users can easily be confused about whether a particular action requires the "select" button or the "enter"

button. The user must memorize, for a particular

function such as selecting an approach, which ofthe

buttons is required for that selection.

Air Traffic Control Experience. Because GPS

approaches are not yet widely used, air traffic controllers do not have very much experience in handling

them. There have been occasions when the controller

was unsure of the location of a particular GPS approach (S. Winter, personal communication, September 25, 1996). This alone is not a human factors

interface design problem, rather it is a training and

experience issue for the air traffic controllers. However, it does become problematic when the controller

issues an instruction, such as changing to a different

runway. This is time consuming using the GPS unit.

Air traffic controllers need to be aware ofthe workload

problems associated with certain instructions and

that pilots may not respond immediately to their

instructions because they are busy reprogramming

the unit. Pilots need to be aware ofhow to handle any

possible controller instruction that could be given

during the approach.

Duplicate Approach Waypoints. For some approaches, the same waypoint may appear more than

once. For example, the Aeronautical Information

Manual (FAA, 1998) states that some approaches

contain the same point for the initial approach

waypoint, the final approach waypoint, and the missed

approach holding waypoint (p. 1-1-49). It is importantthatthe pilot be aware ofwhich ofthese waypoints

is currently active for the unit, as it can lead to an

inappropriate sequencing during the approach. This

can cause the pilot to become confused during a

critical portion of the flight.

Missed Approach Problems. The Aeronautical Information Manual (FAA, 1998), also discusses possible

problems with GPS receivers during the performance of

missed approaches (p. 1-1-49). It states that if a pilot

tries to activate a missed approach prior to reaching the

missed approach waypoint, the unit will set the CDI

sensitivity to ± 1NM and the receiver will not sequence

pastthe missed approach waypoint. The pilot will have

to perform the actions over again once the missed

approach waypoint is reached.
CONCLUSIONS

As with the first paper in this series (Williams,

1999a) it is important, given the problems stated in

this paper, that efforts are made to discover the

frequency of occurrence ofthese problems and what

their effects are on pilot workload and performance.

A primary problem with most receivers is that they

have a large number of available functions, but a

limited number ofcontrols for activating those functions. Also problematic is the manner in which GPS

functionality is implemented. Different procedures

are required for the same functions for every receiver

on the market — even for units made by the same

manufacturer.

The following solutions are offered for improving

some ofthe problems mentioned in this paper and the

previous paper (Williams, 1999a). It is doubtful that

easy solutions exist. However, opportunities for GPS

improvements are presented below for the FAA, GPS

manufacturers, and the end users — the pilots.

FAA Opportunities for Improvement

One suggested solution to the problem ofreceiver

complexity is to reduce the number ofdifferent kinds

of GPS approaches that receivers need to accommodate. The elimination ofoverlay approaches containing procedure turns that require suspension of

automatic sequencing ofwaypoints would eliminate

some of the problems associated with this process.

Most ofthe approaches requiring suspension ofautomatic sequencing are overlay approaches. Overlay

approaches are approaches that were previously established VOR or NDB approaches that have been

redefined by the FAA as GPS approaches. Steve

Jackson, of the FAA Flight Standards Division, has

suggested that "The GPS'T' approach must be established as the standard for WAAS to maximize GPS

receiver capabilities" (personal communication,

February 18, 1998). Operationally, a "T" approach

would normally eliminate the need to suspend

waypoint sequencing (although there might still exist

a need to place an aircraft into a holding pattern

during this type of approach), and would likely

reduce pilot workload during a high-workload portion of flight.

Manufacturer Opportunities for Improvement

Designing an "undo" function on all of these

receivers would keep the pilot from becoming lost

after making an entry error and reduce control inputs

during critical phases of flight. Whether standards

are imposed by the FAA, or volunteered by manufacturers, some standardization ofbutton labels, annunciator panels, and displays is needed. At a minimum,

a core set of GPS functions should be performed in

essentially the same way for every unit on the market.

John Steuernagle, of the Aircraft Owners and Pilots

Association Air Safety Foundation, has recommended

that standardized procedures be designed for the

following set of GPS functions (J. Steurenagle, personal communication, February 3, 1998):

Selecting a waypoint

Establishing a course to or from a waypoint

Selecting and activating an approach

Transitioning to a missed approach procedure

Interruption of autosequencing.

Based on earlier findings, two items that could be

added to this list are the re-activation of automatic

waypoint sequencing, and the selection and activation of an approach to an alternate airport.

A second, though somewhat radical suggestion to

the manufacturers is to reduce the functionality of

the receivers. Anecdotal evidence suggests that most

pilots use only a small amount ofthe GPS functionality on a regular basis. Removing extra functionality

from the units would probably have little effect on

the utility ofthe units. Whether or notit would affect

sales is a separate issue. Manufacturers like to advertise a myriad of functions that a particular unit can

perform. Removing excessive functionality in favor

ofsimplifying the operation ofthe unit makes sense

from a human factors standpoint, but ifit makes the

units less desirable than ones with more functionality, it will never happen.

Pilot Opportunities for Improvement

The Aeronautical Information Manual (FAA,

1998, p. 1-1-49) recommends that, before using any

particular receiver for instrument flight, pilots should

practice GPS approaches under visual meteorological
conditions until thoroughly proficient with all aspects oftheir equipment (receiver and installation).

The pilot should practice:

• Utilizing the receiver autonomousintegritymonitoring (RAIM) prediction function

• Inserting a Standard Instrument Departure (SID)

into the flight plan, including setting terminal

Course Direction Indicator (CDI) sensitivity, if

required, and the conditions under which terminal RAIM is available for departure (some receivers are not SID or STAR capable)

• Programming the destination airport

• Programming and flying the overlay approaches

(especially procedure turns and arc)

• Changing to another approach after selecting an

approach

•Programming and flying "direct" missed approaches

•Programming and flying "routed" missed approaches

•Entering, flying and exiting holding patterns,

particularly on overlay approaches with a second

waypoint in the holding pattern

• Programming and flying a "route" from a holding

pattern

• Programming and flying an approach with radar

vectors to the intermediate segment

• Indication ofthe actions required for RAIM failure both before and after the Final Approach

Waypoint (FAWP)

• Programming a radial and distance from a VOR

(often used in departure instructions).

In addition, Steve Winter, of the FAA Flight

Standards Division recommends familiarization with

the following additional procedures (S. Winter, personal communication, September 25, 1996):

•Recovering from flying past a waypoint where

holding was intended, after failing to place the

receiver in the hold mode

•Adding another waypoint prior to the Initial

Approach Fix (IAF) waypoint after entering the

approach procedure data into the flight plan

• Rejoining the course between two waypoints after

being cleared and proceeding directly to another

waypoint.

Pilots should never assume that familiarity with

one GPS unit will facilitate learning to use another

unit. During the course ofthe operational tests mentioned in this paper, there were several instances of

pilots having difficulty transitioning to the units

used in the test, despite familiarity with their own

GPS units. Pilots should make certain that they are

comfortable and proficient with the unit that is to be

used for that flight. Also, pilots should not assume

that a familiar type of GPS unit will interact with

different avionics displays as expected, due to possible differences in installation procedures.

Finally, as was mentioned in the first paper, if a

pilot becomes totally lost and unfamiliar with what is

seen on the GPS display, he/she should have a backup

procedure ready to implement. Pilots should realize

that GPS units, as currently designed, are not intended to handle any and all navigation tasks. Appropriate use of the systems is both prudent and

recommended. Lessons learned from advanced transport aircraft have shown that turning offautomation

is many times the best solution (Billings, 1996).

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