Experiences raise a number of concerns for future spatial-display developers. While the promise of spatial displays is great, the cost of their development will be correspondingly large. The knowledge and skills which must be coordinated to ensure successful results is unprecedent. From the viewpoint of the designer, basic knowledge of how human beings perceive and process complex displays appears fragmented and largely unquantified. Methodologies for display development require prototyping and testing with subject pilots for even small changes. Useful characterizations of the range of differences between individual users is nonexistent or at best poorly understood. The nature, significance, and frequency of interpretation errors associated with complex integrated displays is unexplored and undocumented territory. Graphic displays have intuitive appeal and can achieve face validity much more readily than earlier symbolic displays. The risk of misleading the pilot is correspondingly greater. Thus while some in the research community are developing the tools and techniques necessary for effective spatial-display development, potential users must be educated about the issues so that informed choices can be made. The scope of the task facing all is great. The task is challenging and the potential for meaningful contributions at all levels is high indeed

Braune, Rolf

Fadden, Delmar M.

Wiedemann, John

English

NASA Technical Reports Server

N90-22951
SPATIAL DISPLAYS AS A MEANS TO INCREASE PILOT
SITUATIONAL AWARENESS
Delmar M. Fadden, Dr. Rolf Braune, and John Wiedemann
Boeing Commercial Airplane Company
Seattle, Washington
At least three elements influence the performance of an operator who must make a system
achieve a desired goal: (1) the dynamics of the system itself, (2) the nature of the possible inputs,
and (3) the means whereby the operator views the information concerning the desired and actual
state of the system (e.g., Pouhon, 1974; Wickens, 1984; and Wickens, 1987). In conventional
airplanes manual control involves the coordination of "inner loop" controls. In this task the pilot is
responsible for continuous manipulation of the controls to compensate for disturbances. Primary
displays (fig. 1) provide the several essential flight parameters which the pilot is required to moni-
tor, interpret, transform, and integrate.
It has long been recognized that intense concentration is necessary for a pilot to achieve high
tracking performance using only "raw data." The underlying need for such concentration stems
from the effort necessary to obtain timely error, error rate, and control input information in each of
the three flight axes. Precision instrument approaches often have higher minimums if a suitable
flight director or autopilot is not available and in use. Most pilots have come to depend on these
aids. Some pilots express doubt about the precision of their own tracking ability any time they are
unavailable.
Flight directors, which came into widespread airline use in the 1960s, aid the pilot in achiev-
ing improved performance by combining the error and error rate information; producing a control
command appropriate to the situation. This command is then compared with the existing control
input and the difference displayed as a steering command. The generation of the steering command
entails automation of several logical and mathematical operations. Of course the pilot must set up
the proper task for the flight director to perform and must follow the steering commands. In typi-
cal applications the automation is sufficiently complete that the pilot has no required intermediate
data-interpretation role beyond that of recognizing and following the steering command.
While use of the flight director improves performance in precision tasks, it does not signifi-
cantly reduce the continuous attention demands imposed on the pilot. Use of a path-following
autopilot mode automates the process one step further by coupling the steering command to the
control surfaces. Relieved of the continuous steering requirement, the pilot is able to devote more
time to other tasks.
Both flight directors and autopilots achieve impressive performance gains. A side effect of
these gains is a reduction in the necessity for the pilot to maintain a high level of awareness of the
elements pertinent to the control task; namely the path error, error rate, and control input. To be
sure, all modem aircraft present these parameters and most airline operating procedures dictate that
the pilot monitor them while using either the flight director or autopilot. However, the monitoring
task is fundamentally different from that of developing a control input given only "raw" data. In
particular, the dynamic decision-making demands of the monitoring task are much lower than those
of the control task.
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https://ntrs.nasa.gov/search.jsp?R=19900013635 2020-03-19T22:06:40+00:00Z
Spatialdisplays,togetherwith enhancedmanualcontrol,offer anopportunityto achievethe
samehighperformanceachievedwith autopilotsandflight directorswhile improvingthepilot's
overall situationalawareness,particularlyduringflight tasksotherthanfinal approach.This is
accomplishedby revisingthesplit of responsibilitiesbetweenthepilot andtheaircraftautomation.
In transportoperations,theneedto alterthevelocity(flightpathangle,trackangle,or speed)
is muchlessfrequentthantheneedto compensatefor wind effects,turbulence,configuration
changes,andspeedchanges.In terminalareaoperations,thenumberof requiredvelocity changes
maybeanorderof magnitudeor morelower thanthoseattitudechangesnecessaryto maintaina
velocity. Furthermore,theneededvelocitychangesaretypicallyseparatedbymanyseconds.By
assigningthevelocity-holdtaskto thebasicflight-controlsystem,themajorityof theattitude
adjustmentscanbemadetransparentto thepilot. Thistypeof controlfreesthepilot from thecon-
tinuousattentionrequirementof attitudesteeringwhilemaintainingthepilot'sdirectinvolvementin
airplaneguidance.
Spatialdisplaysmakeit possiblefor thepilot tobedirectlyinvolvedin developing the path
error information and in selecting the specific tactic to be employed in correcting the error. To
make this practical, current position and velocity information must be displayed in a consistent
context. Operational displays based on work done at Boeing, NASA Langley, RAE-Weybridge,
and other places have shown that a map display, with track angle and speed shown by means of
predicted future positions, provides a suitable context.
The first generation of commercial airline spatial displays are in operation on the Boeing 757
and 767 and the Airbus A-310. These displays take the form of CRT maps with various types of
integral predictors (fig. 2). The format consistency of these displays is quite high and pilot accep-
tance has been exceptionally good. The CRT maps are used for planning and assessing all types of
lateral maneuvers. Direct manual aircraft control is still accomplished by reference to a separate
attitude instrument, but virtually all of the decisions to maneuver laterally can be made looking at
information contained in the map display.
The success of the map display and the potential for flightpath angle and track angle control
to be used on the next generation of commercial aircraft encouraged us to consider expanding the
role of spatial displays. Data from the NASA Aviation Safety Reporting System identifies altitude-
related errors as the single largest category of reported problems (Reynard, Ames Research Center,
1987, personal communication). While the immediate causes of the reported errors are quite
varied, we see a common thread emerging. The pilot's awareness of the vertical flight situation in
most instances does not match the reality of the fight plan, the ATC clearance, or the equipment
setup. A spatial display should be an ideal means of improving the pilot's vertical situation aware-
ness (Baty, 1976).
For most transport flight operations except takeoff and landing, the tracking accuracy
required of the pilot is at least an order of magnitude higher for the vertical task than for the lateral
task. Typical tracking-performance goals as perceived by the pilot away from final approach are
+50 ft of altitude and _+0.5 ° of a VOR radial. At 40 n. mi. from the VOR station, _+0.5 ° corre-
sponds to over +_2000 ft. At this point the accuracy ratio is 40:1. Even on final approach the
vertical accuracy requirements exceed the lateral by at least 2:1. If a conformal 3-D display were
used with sufficient resolution to satisfy the vertical task, the pilot would be overworked laterally.
This concern, along with the difficulty of presenting future trend information in a forward-looking
35-2
display,leadusto concentrateonaseparate2-D side-viewdisplayfor themajorityof vertical
situationinformation (Grunwald,1980;andFilarsky,1983).
Somepastaircraftprogramshavereferredto theattitudedisplayasaverticalsituationdis-
play. Wepreferto usethemoreconventionalterminology,ADI (attitudedirectorindicator)or PFD
(primaryflight display)for theforward-lookingdisplayof attitudeinformationandotherfunda-
mentalflight data. Wereferto a side-lookingorprofile displayasavertical-situationdisplayand
expecthatthepilot wouldobtainthemajorityof overallverticalsituationawarenessfrom thisdis-
play (fig. 3).
Overthepast2 yr wehavebeenexploringwaysof developingausefulandeffectivemeans
to portrayvertical-situationinformation.Thereareanumberof practicalproblemswhichnarrow
thepossibleformatoptionsfor verticalflight information. Theremainderof thispaperwill outline
thelargerhurdlesandindicatewhatprogresshasbeenmadein solvingthem.
Threeissuesappearto befundamentalto thedevelopmentof asuccessfulverticalsituation
display:
1. Handlingof the largedifferencein resolutionrequirementsbetweenthelongitudinaland
verticalflight tasks.
2. Determinationof theappropriatelevelof controlinformationto becontainedin the
instrument.
3. Selectionof adisplaycontextwhichwill beintuitive to thepilot andprovideusefulassis-
tancefor on-andoff-pathverticalmaneuvering.
SCALING ISSUES
The disparity which exists between vertical and lateral resolution requirements applies as well
to vertical and longitudinal information. In fact, since time constraints are seldom tighter than a
minute or more, the difference in resolution requirements can be well in excess of two orders of
magnitude. With this large a difference, equal vertical and horizontal display scaling is clearly
impractical. By using a flightpath predictor we have been able to achieve a balance between verti-
cal tracking performance and the desired path preview capability.
Initial test results indicate that when the vertical situation is presented spatially, a steady
increase in mean deviation from an optimal descent occurs as scale resolution is decreased (fig. 4).
However, even the largest deviation is significantly less than the lowest mean without the spatial
graphics. This result could be attributed to the difference in the tactics the subject pilots employed
to accomplish the task under the two presentations. Without the graphics the pilots had to mentally
integrate various analog quantities according to their own individual rules of thumb. As can be
seen in figure 5, this results in an overall greater deviation from the optimal descent strategy and
more variance among the individual pilot deviations. When given a spatial presentation of the situ-
ation, the subject pilots employed similar path-following tactics, resulting in greater tracking preci-
sion and a lower-rated workload level.
35-3
Thefactof unequalscalescausestheanglerepresentationson thedisplayto beexaggerated
vertically. Throughapreliminarytestserieswefoundthatscaledifferencesof asmuchas20:1do
nothaveanegativeinfluenceon typicalairlineflying tasks.Obviouslyaircraftwith significantly
greaterclimb or descentcapabilitiesthantransportswouldencounterdifficulty at lower-scale
ratios. Whatappearsmoreimportantto thepilotsis thatthelongitudinalscalingof theside-view
displayandthemapdisplaybecongruentsothattherateof movementbetweenthetwo is
compatible.
Anotherresultfrom ourinitial investigationsrevealsthatadigitalreadoutof altitudetakeson
added importance as scale resolution is decreased (fig. 6). In seeking the proper balance between
scale resolution for precision and scale range for preview, it was shown that a digital readout of
altitude provides a good vernier indication while the graphics provides the necessary "big picture"
overview. The graphic spatial information is effective in drawing the pilot's attention to the digital
readout when precise control is needed.
CONTROL ISSUES
In all of today's transport aircraft, manual control is exercised using the attitude display with
follow-up reference to the situational displays. This is the case for map-display-equipped aircraft
as well. Laterally the track angle is two integrations removed from aircraft roll rate, over which the
pilot has direct control. The resulting time delay between control input and map response is too
long for track angle to provide primary inner-loop feedback to the pilot. Even when lateral
acceleration is used to create a prediction of the dynamic path which will be flown, the pilot's pri-
mary control feedback comes from the bank indication on the attitude indicator.
Vertically the conventional control parameter is pitch rate. This term is separated from flight-
path angle by a single integration and some higher-order dynamics. For transports this places the
flightpath response on the order of 1-2 sec behind the control input; long enough to be useless as
the primary feedback term for most situations and short enough to interact negatively with pitch
feedback. The primary dynamic term in the vertical situation is flightpath angle. Furthermore,
flightpath angle, rather than pitch attitude, can be readily assessed in terms of the geometry or
energy conditions of the vertical situation. If the response dynamics of flightpath angle were not
so close to that of pitch attitude, the separation of control and situation assessment, which works
very well in the lateral case, could be established for the vertical case as well.
Beginning with experimental work on the Boeing SST in the late 1960s and continuing
through the early phases of the NASA TCV program, we became convinced that if flightpath
angle, along with suitable situational reference information, is available to the flight crew, the crew
will attempt to use it for control. Without good matching of the control and display dynamics, pilot
workload may well increase.
If a flightpath-angle command-control system is in use, it is possible to display the flightpath
which will be held. This term can be made as responsive as necessary to support the pilot's need
for timely information. If a more conventional control system is used, a filter with appropriate lead
compensation can be added to quicken the dynamics of the flightpath angle information (Bray,
1981).
354
Thekeysituationalelementwhichmakescontrolpossibleis theflightpathpredictionbased
on flightpathangle. Removethepredictionandcontrolrevertsto conventionaltechniques.How-
ever,without theprediction,theusefulnessof thedisplayfor enhancingcurrentsituationalaware-
nessis dramaticallyreduced.Evenmaintainingaconstantaltitudeisdifficult withoutthepredic-
tion. Thusthequestionaboutthedesiredlevelof controlinformationis notanindependentissue.
If thedisplayis to beuseful,it mustcontaindynamicflightpathinformation.Thepresenceof such
informationmeansthatthedisplaywill beusedfor control. Therealissue,then,is how to match
thecontrolanddisplaydynamicsto theinformation-processingcapabilitiesof thepilot.
DISPLAY CONTEXT
The third fundamental issue has to do with matching the frame of reference of the display to
that of the pilot. The vertical component is straightforward. However, the options for the hori-
zontal component are more complex. If information concerning the planned route of flight were
always available and current, then distance along the route would be a good choice. However, the
planned route is not always available. Furthermore, one of the more important uses of the display
is during operations when the airplane is intentionally away from the planned path.
For these situations a narrow slice ahead of the airplane would be more useful. In either case
close coordination between the vertical and horizontal situation displays is essential.
Development work aimed at clarifying the format orientation issue is now under way. We
expect to have an understanding of the major tradeoffs late this year.
CONCLUSIONS
Our experience raises a number of concerns for future spatial-display developers. While the
promise of spatial displays is great, the cost of their development will be correspondingly large.
The cost goes well beyond time and materials. The knowledge and skills which must be coordi-
nated to ensure successful results is unprecedented. From the viewpoint of the designer, basic
knowledge of how human beings perceive and process complex displays appears fragmented and
largely unquantified. Methodologies for display development require prototyping and testing with
subject pilots for even small changes. Useful characterizations of the range of differences between
individual users is nonexistent or at best poorly understood. The nature, significance, and fre-
quency of interpretation errors associated with complex integrated displays is unexplored and
undocumented territory.
Graphic displays have intuitive appeal and can achieve face validity much more readily than
earlier symbolic displays. The risk of misleading the pilot is correspondingly greater. Thus while
we in the research community are developing the tools and techniques necessary for effective
spatial-display development, we must educate potential users about the issues so they can make
informed choices. The scope of the task facing all of us is great. The task is challenging and the
potential for meaningful contributions at all levels is high indeed.
35-5
REFERENCES
Baty, D. L. (1976) Rationale and Description of a Coordinated Cockpit Display tbr Aircraft Flight
Management, NASA Technical Memorandum 3457, November 1976, Ames Research Center,
Moffett Field, CA.
Bray, R. S.; and Scott, B. C. (1981) A Head-Up Display for Low Visibility Approach and Land-
ing. Proceedings AIAA 19th Aerospace Sciences Meeting, January 12-15, St. Louis, MO.
Filarsky, S. M.; and Hover, G. W. (1983) The Command Flight Path Display. Proceedings of the
Society for Information Displays, pp. 196-197.
Grunwald, A. J.; Robertson, J. B.; and Hatfield, J. J. (1980) Evaluation of a Computer Generated
Perspective Tunnel Display for Flight Path Following. NASA Langley Tech Report #1736.
Poulton, E. C. (1974) Tracking Skills and Manual Control. New York: Academic Press.
Wickens, C. D. (1984) Engineering Psychology and Human Performance. Columbus, OH:
Charles Merrill.
Wickens, C. D. (1987) The Effects of Control Dynamics on Performance. In K. Boff and L.
Kaufman (Eds.) Handbook of Perception and Performance. Dayton, OH: University of
Dayton Research Institute.
35-6
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35-10
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35-11
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35-12


Spatial displays as a means to increase pilot situational awareness

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