DOT/FAA/AM-96/16 

Office of Aviation Medicine 

Washington, D.C. 20591 

19960619 029 

A Comparison of the Effects 

of Navigational Display 

Formats and Memory Aids 

on Pilot Performance 

Dennis B. Beringer 

Howard C. Harris, Jr. 

Civil Aeromedical Institute 

Federal Aviation Administration 

Oklahoma City, Oklahoma 73125 

May 1996 

Final Report 

DTIC QUALI'l'Y" ll~SPEC'l'ED 4 

This document is available to the public 

through the National Technical Information 

Service, Springfield, Virginia 22161. 

0 

U.S. Department 

of Transportation 

Federal Aviation 

Administration 
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. 
Technical Report Documentation Page 

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

DOT/FAA/AM-96/16 

4. Title and Subtitle 5. Report Date 

A comparison of the effects of navigational display formats and memory May 1996 

aids on pilot performance 

6. Performing Organization Code 

7. Author(s) 8. Performing Organization Report No. 

Dennis B. Beringer & Howard C. Harris, Jr. 

9. Performing Organlzotion 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 

A great deal of effort has been invested in examining integrated instrumentation for advanced cockpits, but little 

comparable effort has been directed toward the greatest number of aircraft presently flying - those in the general aviation 

environment. This series of studies examined the benefits of a simple and widely available integrated instrument, the 

horizontal situation indicator (HSI), in the performance of simple navigational and orientational tasks by private pilots 

and instructor pilots. Tested in the context of the multiple-processor Basic General Aviation Research Simulator 

(BGARS), the private pilots exhibited significantly fewer navigational reversals and orientational errors when using the 

HSI (in comparison with their performances when using the traditional VOR and directional gyro combination). These 

results were consistent with but even more definitive than those obtained for the instructor pilots. Similar benefits in 

procedural error reduction were also found when instrument index markers, or "bugs," were used as short-term memory 

aids. 

17. Key Words 18. Distribution Statement 

Personal Computer-Based Flight Simulation, Document is available to the public 

Simulator Research, Instrument Flight, through the National Technical 

Display Integration, Psychology, Information Service, Springfield, 

Applied Psychology Virginia 22161 

19. Security Classif. (of this report) I 20. Security Ciassif. (of this page) 121. No. of Pages 122. Price 

Unclassified Unclassified 11 

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

This series of studies was conducted as a part of the Civil Aeromedical Institute (CAMI) general 

aviation (GA) human factors research program which incorporates both near-term and far-term 

objectives. The following mission statement guides the overall effort: 

Conduct applied human factors research in the laboratory and in the field on carefully selected GA problems, to 

obtain objective, scientifically derived data which will aid in identifYing affordable options for reducing the risk 

exposure, and number of incidents and accidents in the general aviation community, and which will serve to enhance 

GA pilot performance under non-routine flying conditions. 

This report resulted from a FY'94-95 effort to consider affordable GA cockpit innovations that 

would provide a more-or-less immediate enhancement of GA pilot performance. 

• The authors thank Dr. Steven Wreggit for his assistance during Sample 3 data collection. 

• Mr. Thomas C. Accardi, Director, Flight Standards Service, AFS-1, sponsored the study. 

• Mr. Robert A. Wright, Manager, General Aviation & Commercial Division (AFS-800) and Mr. 

Michael, L. Henry (AFS-801) provided project oversight. 

• Dr. Thomas McCloy and Dr. Ronald Simmons, Human Factors Division (AAR-100) of the 

Office of Aviation Research, provided Human Factors Program coordination. 

• Mr. Bruce Landsberg, from the Aircraft Owners and Pilots Association and representing the 

General Aviation Coalition, assisted in the selection of the research focus. 

• Dr. Robert E. Blanchard managed the GA program within CAMI. 

iii 
L 

A COMPARISON OF THE EFFECTS OF NAVIGATIONAL DISPLAY FoRMATS AND 

MEMORY AIDS ON PILOT PERFORMANCE 

INTRODUCTION 

Problem 

The separated presentation of navigational data to 

the pilot has long been recognized as imposing additional integration demands. Numerous schemes have 

been devised and implemented to integrate data within 

a common reference frame. One such instrument, the 

Horizontal Situation Indicator (HSI), has seen considerable use and combines the functions of the veryhigh-frequency omni range (VOR) and directional 

gyro (DG) indicators within a single instrument (a 

design suggested by Walter Grether; see Williams, 

1949, as reprinted in Roscoe, 1971). There has been 

little doubt that the HSI simplifies the pilot's task of 

integrating the various pieces of data with some attendant gains in the performance of tracking and orienting tasks. The issue at hand was the cost/benefit 

tradeoff: Did the associated performance enhancements justify the expense of acquiring and installing 

such an instrument in comparatively inexpensive general aviation aircraft? The cost of a HSI head ranges 

from $3200 for a rebuilt nonslaved unit to $4500 for 

a new slaved unit. Installation is potentially in the area 

of$750. A VOR/DG configuration will cost approximately $1000 and is reasonably standard equipment. 

A second question was whether the use of inexpensive memory aids in the form of instrument "bugs" 

(adjustable indices on the display faces) could be used 

effectively to counter the occasional altitude or heading overshoot or reference loss. Add-on altimeter bugs 

can be purchased for as little as $10. A heading bug, 

however, can add $150 to $200 to the cost of a DG or 

HSI (HSis associated with autopilots can be expected 

to have one). These options are more economical than 

altitude and heading preselect systems as found in an 

autopilot, something not likely to be present in most 

single-engined simplex training aircraft. 

A third question addressed in this series of studies 

was how effective a moderate-fidelity flight simulation would be in providing a task context for this type 

of experimentation. The use of personal-computerbased flight simulation has been and is continuing to 

be addressed in the realm of training (Moroney, Hampton, Biers and Kirton, 1994; Williams and Blanchard, 

1995), with additional studies on transfer of training 

using PC-based devices currently under way. Requirements for effective use of these devices for training are 

also presently under examination (Williams and 

Blanchard, 1995). 

Numerous research efforts using high-fidelity simulation systems have been reported over several decades 

and some studies using elaborate networks of PCs 

have appeared recently (Hettinger, Nelson & Haas, 

1994, for example, report a combat aircraft research 

simulation using a network of 23 80486 microcomputers), but few studies have reported on the efficacy 

of moderate-fidelity PC-based flight simulations for 

investigating flight manipulation and navigation tasks 

(Thornton, Braun, Bowers and Morgan, 1992; 

Beringer, 1994; Beringer and Harris, 199 5). Some 

efforts have been reported that use single-computer 

simulations of an aircraft (Kramer, Than, Konrad, 

Wickens, Lintern, Marsh, Fox, and Merwin, 1994; 

Bowers, Deaton, Oser, Prince and Kolb, 1995), but it 

is usually not possible to determine either the fidelity 

of the flight model or the development investment 

from the published accounts. One is usually left to 

compare simulator performance with published handbook performance for the aircraft in question and/or 

rely upon the opinions of subject matter experts 

(SMEs) rated in the specific aircraft. 
The first study of this series had demonstrated that 

some differences in performance could be detected for 

primarily instrument-referenced flight tasks when 

using a moderate-fidelity flight simulation, assembled 

and integrated from off-the-shelf hardware and software, that reasonably well approximated the performance of the aircraft being simulated (by handbook 

reference and SME opinion). However, the task environment did not capitalize on the capability of the 

simulator to support visually referenced maneuvers 

nor did it produce data that were pertinent to use by 

low-experience-level private pilots. The latter studies 

reported here extended the examination of flight 

instrument formats to the private pilot population 

and examined their performance in the context of a 

positive-control scenario requiring flight by minimal 

reference to instruments (altitude and VOR track). 

Integrated Display Format 

These studies were the second and third in a series 

designed to measure the differences in performance 

obtainable with both the VOR/DG configuration 

8 

A 

and the HSI, as well as memory aids. The first study 

(Beringer, 1994) examined the performance of instructor pilots. The second and third studies examined the same displays and memory aids using samples 

of relatively inexperienced pilots. We anticipated that 

these pilots would exhibit greater differences in performance between the integrated (HSI) and separated 

(VOR/DG) display conditions than had the previous 

sample of experienced flight instructors, a number of 

whom had experience with both the VOR/DG instrumentation and the HSI. The principal effects were 

expected to be in orienting to the radial to be intercepted and determining in which direction to turn for 

the intercept. 

The differences between instrument indications 

are shown in Figure 1 for the worst possible case where 

the pilot is instructed to "fly to" the station on the 180 

radial, and sets the VOR head with 180 at the top, 

rather than at the bottom, of the instrument. This alltoo-common error produces reversed depiction in the 

VOR head where the right deviation of the needle on 

the instrument is actually a left deviation relative to 

180 

c 

Figure 1. (A) VORIDG and (B) HSl instruments depicting 

indications for relative position of aircraft (C) with the inbound 

radial selected rather than heading, producing a left-right reversal 

similar to that found for a south heading on a north-up map. 

2 
present heading of the aircraft (the same type of 

problem as found in flying south on a north-up map 

display). The HSI, however, continues to depict the 

appropriate left-right orientation, as the data are 

mapped onto the rotating compass card. 

METHOD 

Design 

The experimental approach selected was a singlefactor within-subject design using navigation display 

type (VOR/DG; HSI) as the independent variable in 

Sample 2. Sample 3 substituted heading and altitude 

bugs (present/absent) as the primary independent 

variable. We selected the repeated measures design 

because we expected high between-subject variability 

in the performance of the flight navigation tracking 

tasks, particularly with the private pilots. Order of 

administration of conditions was counterbalanced 

across subjects for samples 2 and 3. 

Subjects 

Participants were obtained through a contractor 

operating a local fixed-base training operation. Private pilots with less than 200 hours of flight time and 

less than 1 00 hours in the last 6 months were selected 

for both samples (12 each). These individuals ranged 

in age from 18 to 30 years and were all males. Total 

flight experience ranged from 41 to 309 hours (mean 

= 117.1, sd = 72.8) with 3 to 80 hours (mean= 46.6, 

sd = 27.1) having been flown in the previous 90 days. 

Pilots of this experience level were selected because 

they were expected to benefit most from the display 

integration and because they would provide the greatest 

contrast with the instructor pilots examined previously. 

Apparatus 

The Basic General Aviation Research Simulator 

(BGARS), described in detail by Beringer (1994; 

1995) and Beringer and Harris (1995), was used as the 

simulation platform. It was configured as a Beech 

Sundowner for the second and third studies. Participants in the first study flew the simulation as a Beech 

A-36 Bonanza (only the Aero models differed; displays and controls were identical). 

3 

Procedures/Tasks 

All pilots participated in two 2-hour sessions, one 

each at the same time on consecutive days. The first 

session consisted offamiliarization and training. Preparation for the familiarization flight included the reading of a manual explaining the operation of the 

simulator, focusing on the flight instruments and the 

radio interface panel. Subsequent flight familiarization included traffic patterns, constant-altitude standard-rate turns, and VOR radial interception and 

tracking. The second flight scenario, recorded as 

baseline performance, included simulated ATC communications and crosswinds. These two flights were 

conducted using the VOR/DG instrumentation. 

The second day was used for instruction in the use 

of the HSI (sample 2) or instrument bugs (sample 3) 

and for collecting performance data in the two display 

conditions (samples 2 & 3). Two 35- to 45-minute 

courses were used for collecting both tracking and 

turn-and-intercept data. Pilots flew both simplified 

four-leg positive-control scenarios requiring tracking 

VOR radials inbound and outbound, a 270-degree 

turn, ATC-provided vectors, and a visual approach 

(optional ILS approach). Use of the localizer was 

recommended to the private pilots for initial alignment with the runway. The courses were flown with 

full simulated radio communications and involved 

maneuvers and procedures similar to those used in the 

practice scenario. Instructions were given to the participants one course leg at a time, e.g., "Track inbound to the Tinker VOR on the two one zero radial. 

Report crossing the VOR." Subjects received a turn 

instruction to intercept another radial outbound upon 

reporting the VOR. Thus, pilots were not required to 

process or copy a procedure that represented the entire 

course. All turns and vector instructions to intercept 

courselines were provided by the "controller" at the 

appropriate times. 

An additional loading task was included that required the pilot to engage the I DENT function on the 

transponder when requested by ATC. Transponder 

!DENT was used as a probe reaction time task; transponder code, mode, and response time were recorded 

for each event. ATC-pseudopilot communications 
occurred during transmon segments to introduce 

memory interference. All procedures were conducted 

in unlimited-visibility VFR conditions. 

Sixteen data variables were collected at 0.5 Hz, 

including latitude, longitude, altitude, airspeed, heading, magnetic variation, cross-track error, glide-slope 

altitude, DME, and status of marker beacons, gear, 

flaps, and experimenter-entered event marks. Procedural errors were noted by the experimenter and 

simultaneously recorded on videotape. Each pilot was 

debriefed at the conclusion of the session concerning 

the purpose of the experiment. 

RESULTS 

Procedural/ discrete Errors 

Procedural errors were defined for the study as 

those related to the navigation/orientation problem 

and those related to memory of heading and altitudes 

or elements of the verbally issued ATC instructions. 

Navigation/ orientation errors included inappropriate 

setting of the omni bearing selector (OBS), flying 

through radials without any corrective action, and 

turning in the wrong direction for an intercept. 

Memory errors included callbacks for heading, altitude, or radial, failure to recall present assigned altitude, and failure to report VOR and middle-marker 

crossmgs. 

The tabled data could not be directly analyzed as 

frequency data using standard distribution-free tests, 

due to dependence of the data both between and 

within cells. Thus, the number of errors committed 

per individual per condition was tabulated and used as 

an error score; these scores being submitted to analysis 

ofvariance (ANOVA). Table 1 contains frequencies 

of procedural errors by error type, display, and sample 

types, including data from the first study (Beringer 

and Harris, 1995). On the average, pilots committed 

5.3 errors per flight when using the VOR/DG, as 

opposed to 2.8 when using the HSI [F(l,ll) = 5.8; 

p=.035]. The categories that appeared to contribute 

most were turned past heading (3: 1 ratio), heading 

recall (4: 1), and OBS setting incorrect (7: 1). These 

results suggest that the effect is largely one restricted 

to setting and interpretation of the navigation instrumentation, as evidenced by the large difference in the 

number of errors between displays for OBS setting 

and turning past the desired heading for an intercept. 

Table 1. Procedural errors by display type and error category for three samples 

Error Type* 

OBS setting Failed to Altitude Heading Radial Turned past Flew Other Total 

Incorrect Report Recall Recall Recall heading through 

radial 

Private Pilots (12) (Sample2) 

Displays 

VOR/DG 14 19 4 7 23 nd nd 68 

HSI 2 8 0 3 8 nd nd 24 

Private Pilots (11) (Sample 3) 

Displays 

No Bugs 8 18 2 5 2 4 9 25 73 

BUGS 3 7 0 2 0 2 7 22 

Instructors (11) (Beringer and Harris, 1995) 

Displays 

VOR/DG 14 3 3 0 2 nd nd nd 22 

HSI 5 0 2 3 nd nd nd 11 

*(Data omitted for initial wrong intercept turn direction and frequency select errors) 

4 
It is also evident that the workload and additional 

monitoring activity required by the separated instrumentation produced over twice the number offailures 

to report in the VOR/DG condition, as compared 

with the HSI condition. Although the other categorical differences all evidenced trends in the same direction, 

the differences were small. It is noteworthy that these 

differences were obtained despite the fact that training in 

the use of the HSI was comparatively short and did not 

involve any actual flight with the instrument. 

Use of instrument bugs also produced a significant 

overall reduction in procedural errors with an average 

of 5.8 errors committed during flights without bugs 

and 1.9 committed in flights with bugs [F(l,lO) = 

84.05, p<.001]. This effect was a decided contrast 

with the no-difference finding for the use of bugs by 

the instructor pilots. The instructors regularly used 

the heading bug but largely ignored the altimeter bug. 

The private pilots were instructed to always use both 

bugs and were reminded (in the bugs condition) if 

they failed to do so. Although part of the difference 

may be attributable to this procedure, the categorical 

examination of errors does not support the hypothesis 

thatmemotyerrorsweremorelikelywith the instructors. 

The examination of responses to the transponder 

IDENT task indicated no significant differences in 

response times by instrument condition. Observation 

of the pilots during the simulations indicated that the 

task was performed much as one would expect it to be 

in the actual flight environment: without any particular sense of urgency and often with a transmitted 

confirmation of the request prior to the IDENT 

action. This task has limits as to the number of times 

it can be used legitimately during a scenario (at sector 

crossings or hand-offs) without arousing the suspicion of the pilot because instructions to perform the 

task with more immediacy would be contrary to the 

usual practice. Thus, this task may not be useful for 

workload inference without some modification or the 

use of procedures that are somewhat artificial. 

Tracking/Controlling Task Errors 

On the second issue, the problem ofmeasuringrealtime pilot performance of tracking and controlling tasks, 

examination of the track plots indicated consistent 

loss of orientation for many of the pilots when flying 

with the VOR/DG configuration, particularly during 

the 270-degree turn. Flying past/through intercepts 

was also a regular occurrence. Examples of actual 

ground tracks relative to desired paths are shown in 

Figures 2A & B for one pilot to compare the HSI 

course tracking with the VOR/DG course tracking. It 

is evident that better acquisition and tracking performance was obtained using the HSI, consistent with 

···········=~-~:J4 

~ 

Figure 2. Performance with (A) VOR/DG and (B) HSI. Broken lines represent desired tracks. 

5 
the procedural data previously mentioned. Analyses 

of continuous performance data supported this observation, with significantly greater root-mean-square 

errors (RMSE) in cross-track and altitude for the 

VOR/DG condition than for the HSI condition. 

Analyses of continuous performance data for Sample 

3 (bugs/no bugs) showed no significant main effects for 

RMS errors. This is consistent with the use of bugs as 

procedural and memory aids, and not as an aid to course 

or altitude tracking, except to fix the reference point. 

These results were, again, in contrast to those for 

the instructors (Sample 1), who showed no significant 

differences in tracking behaviors across the various 

display conditions. It should be noted that the private 

pilots were given slightly more opportunity to detect 

and correct their errors. In the case of the earlier 

sample of instructors, errors were detected and logged, 

and the pilots were instructed to take corrective actions after their errors were noted. This was done with 

the intent of separating decision making and track 

acquisition from actual course tracking. 

Pilot Subjective Reports 

Responses on the post-test questionnaire indicated 

that pilots perceived the HSI as easier to use than the 

VOR/DG configuration. On a scale of 1 (very difficult) to 6 (very easy), the group (Sample 2) rated the 

VOR/DG as 3.0 (sd = 1.13), whereas they rated the 

HSI as 4.5 (sd = 0.7) [F(1,9)=10.87, p<.01]. Instrument bugs (markers) were also perceived to decrease 

flight task difficulry. Rating of task difficulty with 

and without bugs (Sample 3) averaged 4.36 (sd = 

1.45) and 2.99 (sd = .83) respectively [F(1,10) = 9.3, 

p =.0 12]. Pilots generally reported that the experimental scenarios were more challenging than usual 

flying, presenting a significant workload. This, of 

course, was a positive finding, as the intent was to load 

the pilots sufficiently to detect performance decrements. There were a few complaints from the private 

pilots regarding the degree of "instrument" flying 

required. 

6 

DISCUSSION 

The primary benefits derived from the use of the 

HSI were evidenced in tasks requiring the pilot to 

determine the orientation of the aircraft relative to the 

radial to be tracked, and in simplifying the task of 

setting the VOR head for inbound tracking. Any 

accompanying differences in tracking performance 

appeared to accrue from reduced scanning requirements. The private pilots' attention was often focused 

on maintaining altitude and heading, to the exclusion 

of monitoring track deviation, often resulting in "flying through" the target radial. This behavior was 

greatly reduced or eliminated with the HSI. It is clear 

from the performance data and the subjective ratings 

that both a decided performance benefit and a perceived reduction in workload can be achieved by using 

the HSI display format. The only disadvantages are 

( 1) the relative expense of the device and (2) the need 

to set the HSI for runway heading during an ILS 

approach to obtain proper left-right needle deviations, an action not required by the conventional 

VORhead. 

The benefits of using instrument bugs appear to be 

largely procedural, as expected, and these benefits 

appear to accrue to a number of tasks across the board 

in the form of workload and memory-requirement 

reduction, evidenced by the categorical distribution 

of errors by type. Analyses of performance by segmeiu 

type (inbound, outbound, transition) support this view. 

Both the HSI and instrument bugs could be the 

short-term key to reducing pilot errors if manufacturers can be convinced to produce affordable hardware. 

The passage of time increases this likelihood as display-technology and microprocessor advances make 

possible increasingly flexible and affordable intelligent display systems. This immediate solution to 

navigation problems in the general aviation environment should be followed up by application of the 

appropriate design principles to longer-term display 

solutions for future GA aircraft that may employ 
L 

electronic flight instrumentation systems (EFIS) and 

multi-function displays. The principles of integration 

and memory aiding must continue to be intelligently 

and diligently applied as we move into more advanced 

and flexible means of displaying data in the general 

aviation cockpit. 

This series of studies demonstrates that moderatefidelity PC-based simulation can be used to assess 

pilot behavior in task scenarios of this type. Performances obtained were comparable to those noted for 

more conventional simulators using similar error 

measures {e.g., Kraus, 1973). However, this simulator 

is, ultimately, " ... a box sitting on the ground." 

{Hopkins, 1975). "Howmuchshouldyoupayforthat 

box?" To answer that, we must determine how faithful 

a representation in simulation is necessary to produce 

acceptable generalization of results to the operational 

environment (Williams and Blanchard, 1995). The 

data suggest that devices of the class used in this study 

can produce and support task scenarios that generate 

reasonably representative data. 

REFERENCES 

Beringer, D. B. (1994). Issues in using off-the-shelf PCbased flight simulation for research and training: 

~istorical pers~ective, current solutions and emergmg technologtes. Proceedings of the 38th annual 

meeting of the Human Factors and Ergonomics 

Society, 90-94. 

Beringer, D. B. (1995). Use of off-the-shelf PC-based 

flight simulators for aviation human factors 

research. Washington, D.C: Office of Aviation 

Medicine, TechnicalReportDOT/FANAM-96/15. 

Beringer, D. B. and Harris, Howard C., Jr. {1995). 

~sess~ent of cockpit navigation and memory 

atds usmg PC-based flight simulation. Proceedings 

of the 8th International Symposium on Aviation 

Psychology, {1087- 1091). 

Bowers, C., Deaton, J., Oser, R., Prince, C. and Kolb, 

M. (1995). Impact of automation on aircrewcommunication and decision-making performance. 

International journal of Aviation Psychology, 5(2), 

145-167. 

7 

Hettinger,]., Nelson, W. T. & Haas, M. W. (1994). 

Applying virtual environment technology to the 

design of fighter aircraft cockpits: Pilot performance and situation awareness in a simulated air 

combat task. Proceedings, 38th annual meeting of 

the Human Factors and Ergonomics Society, 115-

118. 

Hokpins, C. 0. {1975). How much should you pay for 

that box? Human Factors, 17(6), 533-541. 

Kramer,A., Than, M., Konrad, C., Wickens, C., Lintern, 

G., Marsh, R., Fox, J. and Merwin, D. (1994). 

Instrument scan and pilot experience. Proceedings 

of the 38th annual meeting of the Human Factors 

and Ergonomics Society, 36-40. 

Kraus, E. F. (1973). A parametric study of pilot performance with modified aircraft control dynamics, 

varying navigational task complexity, and induced 

stress. Savoy: U. of Illinois, Aviation Research 

Lab, TR ARL-73-1 0/AFOSR-73-6/FAA-73-3. 

Moroney, W. F., Hampton, S., Biers, D. W. and Kirton, 

T. {1994). The use of personal computer-based 

training ~evices in teaching instrument flying: A 

comparative study. Proceedings, 38th annual meeting of the Human Factors & Ergonomics Society, 95-

99. 

Thornton, C., Braun, C., Bowers, C. and Morgan, B. 

(1992). Automation effects in the cockpit: A lowfidelity investigation. Proceedings of the 36th annual meeting of the Human Factors Society, 30-34. 

Williams,~- C. (1949). Suggestions concerning desirable dtsplaycharacteristics for aircraft instruments. 

!nterim Report SDC 71-16-4, July 1949; reprinted 

m S. N. Roscoe {ed.), Aviation Research Monographs, 1(1), July 1971, U. of Illinois Institute of 

Aviation. 

Williams, K. W. and Blanchard, R. E. {1995). Development of qualification guidelines for personal computer-based aviation training devices. Washington, D.C.: Civil Aeromedical Institute, Federal 

Aviation Administration, Office of Aviation Medicine Technical Report DOT/FAA/AM-9516.