NASA Technical Memorandum 4744

_.,,_3 _-q /

A Comparison of Two Control Display Unit

Concepts on Flight Management System

Training

Terence S. Abbott

January 1997

NASA Technical Memorandum 4744

A Comparison of Two Control Display Unit

Concepts on Flight Management System

Training

Terence S. Abbott

Langley Research Center • Hampton, Virginia

National Aeronautics and Space Administration

Langley Research Center • Hampton, Virginia 23681-0001

January 1997
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Introduction

One of the biggest challenges for a pilot in the transition to a "glass" cockpit is understanding the flight

management system (FMS). Part of this challenge is

brought about by the complex nature of this system, and

a component of this complexity may be the pilot-FMS

interface (refs. 1-4). For these reasons, a large portion of

transition training is devoted to the FMS. The intent of

the current study was to examine the impact of the

primary pilot-FMS interface, the control display unit

(CDU), on initial FMS pilot training. The hypothesis of

this study was that the interface could significantly

impact training. For this experiment, two CDU interfaces

were developed. One of the CDU's was similar to a

current-generation design, and the other was a multiwindows concept based on graphical-user-interface

(GUI) techniques. For this initial design, both CDU's

were of the same physical size and were as functionally

equivalent as possible, with the graphical interface functionally superimposed over the conventional system.

Further constraints were applied so that the evaluation

could focus primarily on the effects of the multiplewindows and direct-manipulation aspects of GUI

designs. The FMS pilot training was based on a traditional airline training syllabus, but with the training time

severely abbreviated. At the end of the training, an evaluation was conducted in a final, full-mission simulation

context. This paper briefly describes the results of this

study.

Acronyms and Abbreviations

ATC

CBT

CDU

CRT

FMC

FMS

GUI

ILS

ND

SID

STAR

VOR

air traffic control

computer-based training

control display unit

cathode ray tube (display screen)

flight management computer

flight management system

graphical user interface

instrument landing system

navigation display

standard instrument departure

standard terminal-arrival route

very-high-frequency omnidirectional range

Experimental Flight Management System

(FMS) and Control Display Unit (CDU)

Concepts

An experimental FMS was developed as a highly

flexible tool for the further development and evaluation

of both advanced FMS guidance algorithms and interface

concepts. The FMS databases included U.S.-wide information on very-high-frequency omindirectional ranges

(VOR's), low- and high-altitude airway structures, airports, and the geometry of airport instrument landing

system (ILS) and runway configurations. Databases also

were included for specific standard instrument departures

(SID's), standard terminal-arrival routes (STAR's), and

approaches for a limited number of selected airports. Performance optimization was based on a Boeing 757 class

of airplane that was also the performance model for the

airplane simulator used in the evaluation. This optimization provided climb, cruise, and descent schedules; fuel

flow estimation; estimated waypoint crossing speeds and

altitudes; and waypoint arrival-time estimation. The

algorithms also accommodated pilot-entered climb,

cruise, or descent speeds; cruise altitudes; and waypoint

speed and altitude crossing constraints. The FMS could

simultaneously handle four paths or profiles: a primary

or active path, a modified active path, a secondary path,

and a data-link path. The navigation display (ND) on the

simulator instrument panel could display a primary or

active path and either a modified active path or a secondary path.

Two CDU concepts were developed for this study: a

generic, basetine concept and a graphical-user-interface

(GUI) CDU concept. Both CDUs used the same underlying experimental FMS software that included the databases, path-definition routines, and path-optimization

techniques. Because of the requirement for a flexible

interface, the CDU's were physically implemented on a

10-in. diagonal, 16-color liquid-crystal, flat-panel display, which allowed both concepts to be implemented on

the same physical device. Operator input was provided

via a touch panel that overlaid the flat-panel display.

Baseline CDU

The generic, baseline CDU, based on the Boeing

FMS concept, generally was modeled after the Boeing

747-400 CDU (ref. 5). The actual aircraft CDUs are

approximately 10 in. diagonally with a 5.5-in. diagonal

CRT. As noted previously, color flat-panel displays were

used to emulate these devices. These CDUs employed

left and right line-select keys, dedicated function keys,

and alphanumeric keys for data entry.

For this study, the baseline CDU (fig. 1) had several

significant differences from the system on which it was

based. Probably the most obvious difference was the

"soft" interface, which used the liquid-crystal display

(LCD) and touch-panel combination instead of an actual

keyboard. This soft interface did not provide the tactile

feedback associated with real button interaction. However, because key-press data-entry errors were not an
Figure 1. Baseline CDU with representative page.

experimental issue for this study, this lack of tactile

feedback was not considered to be a significant factor.

The second difference between this baseline CDU and its

real-world counterpart was in the line length on the emulated cathode ray tube (CRT) display screen. The emulated CRT for the baseline CDU was a 14-line by

30-character display, while the actual CDU uses a

14-line by 24-character display. This 30-character capability allowed for the display of long waypoint names

without the need for name sequence coding. For example, a place-bearing-distance waypoint wherein the place

was DEN, the bearing was 123 ° , and the distance was

50 mi. would be displayed as "DEN I 23/50" on the baseline CDU, while an actual CDU would display "DEN01"

(where 01-49 are unique sequence numbers for special

waypoints associated with DEN). The last major difference was the use of color coding on the emulated CRT of

the baseline CDU. Data entry box prompts were colorcoded according to the following scheme: magenta was

used for FMS initialization data (e.g., zero fuel weight or

the departure airport), green was used for performance

enhancement data, and white was used for all other

entries. Magenta was used on the title line of each routespecific page to identify the active route, as well as to

color code the active waypoint data on the page displaying the individual legs of the flight plan (the route legs

2

page, "RTE LEGS"). It should be noted that the CRT on

an actual 747-400 CDU is a monochromatic device.

Graphical CDU

The experimental graphical CDU was founded on

GUI concepts that can be seen in the early Xerox PARC

(Xerox Palo Alto Research Center) designs (ref. 6) and

are probably best exemplified in the Apple Macintosh

computer interface (ref. 7). For both application and

evaluation reasons, constraints were applied to this

implementation to maintain as much similarity as possible with the conventional CDU. The interfaces were of

the same physical size and were as functionally equivalent as possible, with the graphical interface functionally

superimposed over the conventional FMS. This constrained approach was taken for several reasons. From an

application standpoint, physical size was maintained to

support the potential for hardware retrofit of this type of

technology into the current commercial aircraft fleet.

From an experimental perspective, this initial design was

aimed primarily at evaluating the effects of the multiplewindows and direct-manipulation aspects of GUI designs

compared to conventional designs. To support this focus,

the following design constraints were used (relative to

the baseline CDU): maintain the same physical size, use

an equivalent number of "pages," use a similar or equivalent hierarchy of page structures, maintain the same terminology, and use the same underlying functionality.

Given these constraints, three major features that are

familiar to GUI users were not used: pull-down menus,

resizable windows, and window scroll bars. The graphical equivalent of the baseline CDU is shown in figure 2.

In this example, the waypoint "DEN352/18" could be

edited by touching the line on the CDU containing the

data for DEN352/18. A waypoint entry window would

then be displayed over the existing LEGS window

(fig. 3). This edit window would display all of the available edit options for DEN352/18 and, in a partially

masked fashion, options that are not currently valid for

this waypoint.

Evaluation Design and Conditions

This study was conducted to evaluate interface

effects on pilot training. The evaluation approach was to

develop and use a minified, airline-type training environment that focused on the pilot-training aspects of the

FMS. The target subject pools for this evaluation were

those pilots who would be potential candidates for a transition from an older generation flight deck to a "glass"

cockpit. The minimum pilot selection criteria were a

commercial pilot's license with instrument rating, no

prior FMS training, and recent experience in a paid piloting position. Flight instructor positions did not qualify

for the paid-position requirement. Sixteen pilots were
Figure2.Graphical CDUwithrepresentative page. Figure3.Graphical CDUwitheditwindow.

used,withthepilotssplitequallybetweenthetwoCDUs.

Theentiretrainingandevaluationsessionfor eachpilot

wasconductedinasingledaythroughtheuseofahighly

structuredtrainingsyllabus.Thetrainingincludedsessionsin anaircraftsimulatorandacomputer-based trainingsystem.Theevaluationwasconductedintheaircraft

simulator.

Aircraft Simulator

The fixed-base flight simulator used in this study

was a generic two-engine transport with performance

characteristics equivalent to a Boeing 757. This simulator provided full-mission capability with models of most

major aircraft systems. Flight deck features included a

fly-by-wire side-stick control system and electronic

flight displays (captain and first officer). The features

relative to this experiment were the ND's and the physical placement of the CDU fiat-panel displays. The ND's

were used in a map mode where the lateral paths generated by the FMS were displayed. The fiat-panel CDU's,

placed in front of and slightly to the right of each pilot,

were mounted at an angle of approximately 15 ° from the

horizontal on a surface that allowed the pilots to rest the

heels of their hands while interacting with the CDU.

Knowledge of the control characteristics and the aircraft

systems was not considered a factor in this experiment

because the subjects were not required to fly the aircraft nor were they responsible for aircraft systems

management.

Air Traffic Control (ATC) Simulation

To add operational realism, an ATC simulation was

used during the latter part of the simulator training sessions and during the evaluation session. This simulation

included a remote ATC controller's station and an audio

communication link with the aircraft simulator. In addition to the geographical information normally shown at

the controller's station, this simulation could also display

the flight plan routes generated by the aircraft simulator

b-MS.

Computer-Based Training (CBT)

A CBT system was developed to support this test.

This system, modeled after airline training systems for

FMS training, consisted of two personal computers that

were connected over a communication network. One of

the computers represented the FMS used in the flight

simulator. This computer used a color CRT with a touchpanel interface to mimic the CDU of the flight simulator.

The second computer modeled the simulated aircraft and
provided the training subject with an ND that presented

information in a fashion similar to that of the ND in the

flight simulator. This training system included an operator's manual for the appropriate CDU, a short "how-to"

document, and a 50-task training syllabus. The syllabus

was a superset of the tasks that were used in the

evaluation.

Training Sequence and Syllabus

The sequence of events for each pilot was (1) an initial briefing, (2) an introductory session in the flight simulator, (3) two CBT sessions, (4) a second training

session in the flight simulator, and (5) the simulator

flight evaluation. This sequence is shown in table 1. The

simulator training sessions and the CBT were structured

around a planned flight from Los Angeles International

Airport to San Francisco International Airport. The FMS

tasks used in the simulator sessions are as follows:

1. Initialize FMS.

2. Enter initial route.

3. Check navigation radios.

4. Proceed directly to a waypoint.

5. Change the climb airspeed.

6. Retrieve route information.

7. Proceed directly to a waypoint not on route.

8. Divert to origin airport.

9. Build an approach path.

10. Insert and delete holding pattern at fix.

11. Change a speed constraint at a waypoint.

12. Change a runway on final approach (session 2

only).

Table 1. Training Sequence

Time,

Session min Topics

Initial briefing 30 Overview

Description of simulator

Introduction to FMS

concepts

Flight simulator introductory session

110

CBT session 1 50

CBT session 2 80

Second flight simulator 60

Simulator flight 60

evaluation

Simulator familiarization

Introduction to FMS/CDU

Introduction to ND

Initial FMS training

Begin CBT tasks

Complete CBT tasks

Reinforce CBT skills

4

Two pilot confederates acted as training instructors

for the initial briefing and the two simulator training

periods. They also assisted in the development of the

evaluation tasks, criteria, and scenarios. During the evaluation portion of the test, one of these pilot confederates

functioned as the copilot and performed duties as the

"pilot flying."

Evaluation Conditions and Tasks

The evaluation scenario and tasks, similar to the

prior simulator training and CBT sessions, were

1. Initialize FMS to include the initial route entry.

2. Taxi out with a runway change.

3. Intercept a departure radial to a VOR.

4. Insert a waypoint and proceed direct.

5. Build an approach path.

6. Display an abeam waypoint.

7. Insert a holding pattern at a fix.

8. Change landing runway.

The major distinction was that the proposed flight plan

was now from Denver Stapleton International Airport to

San Francisco International Airport. For the evaluation,

duties of the subjects were limited to FMS interaction.

All other duties were the responsibility of the pilot confederate. During the test, the subjects were requested to

briefly verbalize their actions by using a verbal protocol

technique. In addition, the simulation was stopped temporarily after an evaluation task was performed. At that

time, the subjects were required to complete a short questionnaire. A pilot debriefing with an associated questionnaire was completed after the evaluation session.

Results

Qualitative Results

After finishing each evaluation task, the subjects

completed a short questionnaire that included five items:

two yes-or-no questions and three rating questions. The

two yes-or-no questions were (1) "Could you perform the

task in the time allotted?" and (2) "Could you perform

the task with the FMS?" If either of these questions was

answered "no," the questionnaire was considered to be

completed for that task. The remaining three questions,

questionnaire items three through five, dealt with the

translation into FMS actions or understanding of a

requirement (e.g., an ATC clearance), the ease of performing the actual task on the FMS, and the speed with

which the subject completed the task. The subjects were

briefed that correct task performance was significantly
moreimportantthanspeed.Forthefirst two questions,

the resulting differences in the responses were not significant. For the last three questions, only differences in the

responses to question 3, concerning the translation into

FMS actions or understanding of a requirement, were

found to be significant. From the responses to question 3,

the graphical CDU received a more favorable rating

than the conventional CDU. A possible explanation of

this result is given in the "Additional Observations"

section.

Quantitative Results

After completion of the data collections, the two

pilot confederates rated each task for each subject on

both a pass-fail basis and on a scale of I to 5. (See appendix.) These ratings were done with a combination of

video data, written notes, and FMS-recorded keystroke

data. Ratings were then analyzed by tasks.

For the pass-fail analysis (table 2), only the ratings

for task 3 (intercept a radial to a VOR) were significantly

different. For this task, the graphical CDU provided better performance than did the conventional CDU. A possible explanation of this result is given in the "Discussion

of Results" section.

Table 2. Number of Passing Scores By Task

Passing scores for task number--

Control display unit I 2 3 4 5 6 7 8

Conventional 3 6 1 7 3 4 7 8

Graphical 2 8 7 7 3 5 8 7

Table 3. Composite 1-to-5 Scores By Task

Composite scores for task number--

Control display unit 1 2 3 4 5 6 7 8

Conventional 25 14 31 10 25 15 15 8

Graphical 27 11 10 11 27 19 10 12

The results for the 1-to-5 ratings (table 3) were similar to the pass-fall results. Again, only the ratings for

task 3 (intercept a radial to a VOR) were significantly

different. For this task, the graphical CDU provided better performance than did the conventional CDU.

Discussion of Results

Considering that only one of the eight tasks showed

a significant performance difference in favor of the

graphical design, an assumption could be made that a

graphical interface approach to CDU design may not be a

worthwhile endeavor. However, researchers noted in

analyzing the results from task 3 (intercept a radial to a

VOR) that there appeared to be better task mapping

between the task requirements and the interface for the

graphical CDU. That is, the graphical CDU waypointedit window, by segregating the waypoint options into

functional groups, probably contributed to the subjects'

ability to identify and select the appropriate option. In

addition, to perform this task with the conventional

CDU, the subjects initially had to make the VOR waypoint the first waypoint on the route legs before the intercept course could be entered. With the graphical CDU,

the subjects only needed to select or "edit" the VOR

waypoint and then enter the radial course. While this

result was not unexpected (refs. 8 and 9), it was surprising that the other graphical features did not have a larger

positive effect.

Additional Observations

In addition to the formal data, an examination of

notes made by the pilot confederates and the experimenters led to several observations on the results. One of the

most striking observations was the similarity in the confusion experienced by the pilots with both CDU's,

caused by the use of abbreviations and acronyms for

function key labeling. Coupled with this use of abbreviations and acronyms is the fact that even when these

phrases are understandable, they may not be meaningful.

That is, the phrase "VNAV" for vertical navigation may

not intuitively bring to mind the association "climb,

cruise, and descent data." Furthermore, this functionlabeling scheme probably led to one of the more fundamental problems observed in the training: the CDU

functions did not always match the tasks the pilots were

trying to perform. This mismatch was especially true for

ATC clearances that required FMS interaction where the

language of the FMS usually did not match the language

of the clearance. The last observation noted was in regard

to the page or window hierarchy. For the initialization of

the FMS and the initial route entry, both CDU's provided

a mechanism that allowed for a logical progression

through the various windows, with one exception. To add

a departure runway or SID, the pilots were required to

deviate from the normal sequencing. This need to deviate

led to some confusion during entry of the initial route

data. In addition, for the conventional CDU, there was

not an explicit function hierarchy (no hierarchical index).

While one was provided for the graphical CDU, it was

not necessarily used. Also, as noted in reference 8, "one

of the major sources of difficulties for new and experienced users uncovered in our studies was the mismatch

in many cases between the task defined by an Air Traffic

Control (ATC) clearance and the organization of the

operations required to program the FMC to quickly carry

out these directives." Overall, the combination of the less
thanoptimumfunctionhierarchyand the mismatch

betweenATCclearancesandthepilots'taskto implement thoseclearanceswas the largestdeficiency

observedduringthisstudy.

Concluding Remarks

This initial study examined the impact on pilot training of the use of a graphical control display unit (CDU).

Design constraints applied to this preliminary concept

emphasized the effects of the multiple-windows and

direct-manipulation aspects of the graphical user interface (GUI) design. The results of this study showed marginally better pilot performance and subjective ratings

for the graphical CDU over the conventional design.

However, while some advantages were noted with this

design, the constraints imposed on this initial implementation potentially minimized major, operationally significant benefits. From an informal analysis of the

performance data and experimenter observations, it

appears that greater benefits could be obtained by a

design that focuses on two aspects of the pilot-system

interaction. First, functions need to be provided that more

directly support pilot operational tasks, especially in the

area of air traffic control (ATC) clearance requirements.

Second, a window or page hierarchy must be provided

that offers a natural linking and tractability mechanism

between these functions. Future designs that support

these goals should exhibit reduced pilot training requirements and improved pilot flight management system

(FMS) performance.

NASA Langley Research Center

Hampton, VA 23681-0001

October I, 1996
Appendix

Scoring Method

Each task was rated with both a pass-fail rating and a numeric scale. Table A1 details the score, criteria, and criteria

definitions for each level.

Table AI. Scoring System

Score Criteria Criteria definition

1 Subject makes no errors • Time to complete the task is not a factor as long as it is within the

allocated time.

• Repeating clearances, spelling of words, and explanation of the situation does not constitute help.

• Input errors and software failures are not considered as errors.

• Suggestions about how to operate the interface (e.g., finger position)

are not considered as help.

• Circuitous methods are not considered as errors.

• A single, unsolicited confirmation of a modified route from the pilot

confederate does not constitute help.

2 Subject makes an error but corrects it • All elements for a score of 1 apply.

without help • Errors include any cognitive error or wrong procedure, among others.

3 Subject makes an error and corrects it

with minor help

Subject makes an error and corrects it

with major help

• All elements for a score of 1 apply.

• Minor help includes confirming past actions or drawing attention in a

general way, but does not include drawing attention in a pointed way,

providing the subject with choices, or telling the subject what to do.

• Minor help is generally characterized by open-ended questions.

• Minor help includes:

- Confirming past actions, such as, "O.K." or "Looks good."

- Drawing attention in a general way, such as, "On what page do you

find abeam information?"

- A single oblique clue such as, "What are you trying to do?" or "How

do you open the option window?"

- A single peripheral clue, such as, "You might want to clean up the

screen."

• All elements for a score of 1 apply.

• Major help includes drawing attention in a pointed way, providing the

subject with choices, and telling the subject what to do.

• Major help includes:

- Drawing attention in a pointed way, such as, "Are you trying to construct a waypoint or go to a waypoint?"

- Providing the subject with choices, such as, "You can enter the runway information while you are on this page or do it later."

- Telling the subject what to do, such as, "Press the DELETE key."

- A core clue involving a key concept of the task, such as, "You need

to put DBL in 1L." or "No, not that."

- Multiple minor clues.

- Any direct instruction regardless of whether it is a core or peripheral

issue.

5 Subject is unable to complete the task • Time to complete the task is not a factor as long as it is within the

allocated time.
References

1. Dodd, Robert S.; Eldredge, Donald; and Mangold, Susan J.: A

Review and Discussion of Flight Management System Incidents Reported to the Aviation Safety Reporting System.

Battelle Columbus Labs., 1992, FAA. (Available from DTIC

as AD-A252438.)

Mann, Teresa L.; and Morrison, Jeff G.: Effects of Display

Density and Format Type on Control Display Unit Format

Design. Proceedings of the 7th Digital Avionics Systems Conference, IEEE, 1986, pp. 330-337.

Sarter, Nadine B.; and Woods, David D.: Pilot Interaction

With Cockpit Automation---Operational Experiences With the

Flight Management System. Int. J. Aviat. Psychol., vol. 2,

no. 4, 1992, pp. 303-321.

4. Sarter, Nadine B.; and Woods, David D.: Pilot Interaction

With Cockpit Automation--II: An Experimental Study of

5.

6.

7.

8,

9.

Pilots' Model and Awareness of the Flight Management System. Int. J. Aviat. Psychol., vol. 4, no. t, 1994, pp. 1-28.

Honeywell, Inc.: B747-400 Flight Management System Guide.

Pub. No. C28-3641-12, 1989.

Norman, Donald A.; and Draper, Stephen W.: User Centered

System Design--New Perspectives on Human-Computer Interaction. Lawrence Erlbaum Assoc., Inc., 1986.

Apple Computer, Inc.: Macintosh Human Interface Guidelines. Addison-Wesley Pub. Co., 1992.

Polson, Peter; Irving, Sharon; and Irving, J. E.: Applications of

Formal Models of Human-Computer Interaction to Training

and Use of the Control and Display Unit. Tech. Rep. 94-08,

Univ. Colorado, 1994.

Abbott, Terence S.: Task-Oriented Display Design--Concept

and Example. Aerospace Technology Conference and Exposition, SAE, 1989. (Available as SAE Tecb. Paper Ser. 892230.)

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January 1997 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

A Comparison of Two Control Display Unit Concepts on Flight Management

System Training

6. AUTHOR(S)

Terence S. Abbott

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-0001

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

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13. ABSTRACT (Maximum 200 words)

One of the biggest challenges for a pilot in the transition to a "glass" cockpit is understanding the flight

management system (FMS). Because of both the complex nature of the FMS and the pilot-FMS interface, a large

portion of transition training is devoted to the FMS. The current study examined the impact of the primary pilotFMS interface, the control display unit (CDU), on FMS training. Based on the hypothesis that the interface design

could have a significant impact on training, an FMS simulation with two separate interfaces was developed. One

interface was similar to a current-generation design, and the other was a multiwindows CDU based on graphical

user interface techniques. For both application and evaluation reasons, constraints were applied to the graphical

CDU design to maintain as much similarity as possible with the conventional CDU. This preliminary experiment

was conducted to evaluate the interface effects on training. Sixteen pilots with no FMS experience were used in a

between-subjects test. A time-compressed, airline-type FMS training environment was simulated. The subjects

were trained to a fixed-time criterion, and performance was measured in a final, full-mission simulation context.

This paper describes the technical approach, simulation implementation, and experimental results of this effort.

14. SUBJECT TERMS

Flight-management system; Control display unit; Graphical user interface

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