*. 1 

NASA Technical Memorandum 1021 87 

Display-Based Communications 

for Advanced Transport Aircraft 

Alfred T. Lee 

(NASA-TH-102187) DISPLH-BBSED N89-24790 

CO!lMUtiZCATIOIS FOB ADVANCED TBAlSPORT 

AIRCRAFT (NASA. 24 P I Ames Research Center) CSCL 12A Unclas 

G3/54 0216753 

May 1989 

NASA 

National Aeronautics and 

Space Administration 
~~ 

NASA Technical Memorandum 1021 87 

Display-Based Communications 

for Advanced Transport Aircraft 

Alfred T. Lee, Arnes Research Center, Moffett Field, California 

May 1989 

National Aeronautics and 

Space Administration 

AmesResewchcenter 

Moffett Field, Wiomia 94035 
SUMMARY 

The next generation of civil transport aircraft will depend increasingly upon ground-air-ground and 

satellite data link for information critical to safe and efficient air transportation. This paper reviews 

previous studies which have examined the concept of display-based communications in addition to, or in 

lieu of, conventional voice transmissions. A full-mission flight simulation comparing voice and displaybased communication modes in an advanced transport aircraft is also described. The results of this study 

indicate that a display-based mode of information transfer does not result in significantly increased 

aircrew workload, but does result in substantially increased message acknowledgment times when 

compared to conventional voice transmissions. User acceptance of the display-based communication 

system was generally high, replicating the findings of previous studies. However, most pilots tested 

expressed concern over the potential loss of information available from frequency monitoring which 

might result from the introduction of discrete address communications. Concern was expressed by some 

pilots for the reduced time available to search for conflicting traffic when they were using the communications display system. The implications of the findings for the design of display-based communications 

are discussed. 

BACKGROUND 

Each day thousands of scheduled air carrier operations occur within the National Airspace System 

(NAS). Communications vital to these operations are transmitted via radio from sites distributed across 

the country. The limitations in conventional radio transmissions as the primary medium of information 

transfer in the NAS are apparent by the large number of reports identifying air-ground information 

transfer problems to the Aviation Safety Reporting System (ASRS). Reviewing the reports of 

1978-1980, Billings and Cheaney (1981) found that nearly three-fourths of the incidents involved some 

type of information-transfer problem (whether within the cockpit, among ground controllers, or between 

air and ground stations). Of the reports received in 1985 and 1986, one-fourth were a result of a failure 

in air-ground information transfer (Lee and Lozito, 1989). In both studies, most of these problems were 

the result of human error rather than equipment failure. The most common communication problems in 

air-ground communications were attributable to pilot misunderstandings of air traffic control (ATC) 

clearances or a failure to remember the message caused by preoccupation with other duties. 

These findings are not surprising when it is understood that radio communications in dynamic environments rely heavily on the capability to rapidly process information and execute directives, often 

when the aircrew is preoccupied with other duties. As the airspace becomes more congested and as 

experience levels of aircrews decline, information-transfer errors attributable to limitations in information processing will become more common. 

It is often argued that improved communications discipline and training will significantly reduce 

communication errors. However, decades of refining the language and procedures of air-ground 

communications have not resolved the problems inherent in the use of spoken language in the aviation 

environment. Not the least of these limitations is the propensity for the strict phraseology of 

1 
communications to deteriorate under the highly routinized civil air transport environment. Violation of 

standard communications procedures can have tragic consequences. The worst aviation accident in history (at Tenerife in 1977) was the result of using nonstandard phraseology in a takeoff clearance 

exchange. 

In the decade to come, the nation’s airspace system will undergo significant changes in the means by 

which information is transferred between aircraft and ground stations. Increasingly, ground-air-ground 

information transfer will rely upon digital data link via satellite and ground-based radar sites (Mode S) 

and over VHF/FM station subcarriers. Some data link services are already provided by private industry 

(e.g., Airline Communication and Receiving System (ACARS)) and more services are slated for introduction as a part of the planned modernization of the ATC system. It is the eventual use of data link as 

the principal communications medium of the future that introduces the need to ensure that the system is 

designed to support the task of the human operator both on the ground and in the air. 

Flight Deck Integration 

The flight deck integration issues introduced by data link communications have been the focus of 

several studies both in the United States and abroad. One of the first studies to evaluate the use of data 

link for ATC services is reported by Diehl (1975). Using the then-current display technology, a 

comparison of various methods of information presentation was conducted. In a series of B-737 and 

DC-9 aircraft simulations, ATC message response times by test aircrews and aircrew ratings of device 

acceptability were measured. Response times to messages displayed visually, by synthetic voice, or by 

both, averaged about 7 sec. Response latencies to synthesized voice message averaged some 30% longer 

than either visual display alone or simultaneous visualhoice display. User acceptability was rated high, 

particularly for visual and print display of messages during high-workload flight phases, although some 

pilots disliked data link during ground-proximate operations (e.g., missed approach). No differences 

were found among the methods of presentations between the two- and three-crewmember simulations. 

A more recent study by Uckerman and Radke (1983) examined the potential effect of airborne data 

link communications on the visual workload of Airbus A-300 transport aircrews. With the advent of 

two-person crews, there is concern that higher visual workload within the cockpit may increase the likelihood that potential conflicting traffic will not be sighted. An airborne terminal data link communications system, with its reliance on visual displays, may reduce external cockpit vigilance even further. 

The results of this study did not support the belief that the introduction of display-based communications 

(in this case a conventional Control Display Unit (CDU)) will adversely affect visual traffic scanning 

behavior during simulated approaches. This finding has been supported by others (Waller and Lohr, 

1989). As with the earlier study by Diehl(1975), judged aircrew acceptability was generally high for the 

airborne terminal concept. 

The possibility of using a display-based communications system for light, general-aviation aircraft 

was investigated by Parker and associates (Parker, Duffy, Christiansen, 1981; Parker and Duffy, 1982). 

Single-pilot, instrument flying is arguably the most demanding task in aviation. Particularly difficult in 

the high-workload environment of single-pilot instrument flight is the accurate retention and readback of 

ATC clearance information. Displaying such information could relieve much of the pilot’s workload 

I 2 
associated with retaining this information in memory or having to write it down while busy with other 

flight duties. In the studies by Parker et al. (1981), a display-based communications system with voice 

transmission as a backup was compared to conventional voice. The voice backup allowed the pilot to 

update weather and automated terminal information service (ATIS) data, and to clarify and confirm controller messages. No differences in subjectively rated workload were found for any phase of flight. As 

with previous studies, pilot acceptance of the data link communications concept was high. The provision 

of a voice backup was considered to be an improvement to display-based communications by the pilots 

and was generally perceived as an enhancement to safety. 

Advanced Technology Aircraft 

The potential benefits of data link technology used as a communications medium for ATC and advisory information, as well as for other types of information concerning weather and navigation, will not 

be realized unless it can be demonstrated that such technology will improve the process of air-ground 

information transfer when it is compared to the existing conventional voice system. There are two 

essential criteria by which the utility of a communications system can be measured. First, the speed at 

which information is transmitted, displayed, understood, and acknowledged (the information-transfer 

issue). Second, the ease and efficiency by which messages can be composed and transmitted by the user 

(the interface issue). The user, in this case the pilot, is unlikely to use a new communications system 

which either does not enhance the transfer of information or requires the use of a system interface which 

is difficult to use. Certainly it would be unacceptable to introduce systems which might delay 

communications, result in a net increase in workload, or result in reduced safety of operations. 

Data link technology as a principal communications medium in cockpits will evolve at a time when 

the common crewmember size will be two (rather than three), and conventional analog instrumentation 

will be replaced by information displayed electronically. Furthermore, many tasks previously performed 

by crewmembers will be partially or fully automated. These changes to the context within which displaybased communications occur require studies to be conducted which will approximate that operating 

environment. In order to investigate the potential effect of display-based communications in these future 

air transport cockpits, a full-mission, flight-simulation study was conducted in which a prototype data 

link communication system was compared to conventional voice communications for an advanced 

cockpit. While assessments of relative communication response times by pilots and measures of 

workload during flight-critical times were of particular interest, the study also provided an opportunity to 

observe and record aspects of pilot behavior which might affect other aspects of flight deck information 

management such as intracrew communications. 

METHOD 

Participants 

Eight air-transport pilots currently flying scheduled air-carrier aircraft participated as paid volunteers 

in the study. Six of the pilots flew in the First Officer crew,position and two flew as Captains at the time 

3 
of the study. Flying experience ranged llom 5,000 to more than 20,000 hr. For the purposes of this study, 

pilots served in the copilot (right seat) capacity as pilot-not-flying; the left seat (Captain’s) position was 

occupied by an experienced airline pilot who carried out the normal duties of pilot flying. This pilot was 

employed as a simulator manager at the facility. 

Apparatus 

A generic, advanced, transport-aircraft flight simulator located at Ames Research Center was used 

for the study. A detailed description of the simulator may be found in Sexton (1983). The aircraft simulated is a medium-range, twin-turbojet civil transport of the mid 1990s. Instrumentation is provided on 

five color cathode ray tubes with primary control inputs provided by a side-arm, force feel control stick. 

The simulator has a fixed base with a single-channel, two-window visual attachment which provided the 

aircrew with a computer-generated, external visual scene. 

For display-based communications, each pilot used a communications terminal located on a horizontal flight desk adjacent to the instrument panel. The terminal consisted of a 7 in. (horizontal) by 4 in. 

(vertical) electroluminescent display capable of generating 5 X 7 dot-matrix alphanumeric characters in a 

40-character by 12-line configuration. All operator inputs were by touch points adjacent to message lines 

or characters. The pre-formed messages and menu architecture were adapted Erom prototypes developed 

by Boeing in 1987. The menu architecture is shown in appendix A. The main data link menu includes a 

selection for an ATC uplink page. This page was used to display ground-to-aircraft uplinks existing in 

the terminal’s message buffer. Displayed ATC messages were verbatim transcripts, excluding call sign, 

of normal controller voice communications. Noncontrol information, such as weather alerts and ATIS, 

were also provided in verbatim form. 

Air-ground transmissions such as clearance and weather requests could be initiated at any time by 

selecting the appropriate message request menu, selecting the desired message and touching the SEND 

message point located on each request page. An asterisk was displayed next to each selected message to 

provide the pilot with a confmation of message selection. Where necessary, alphabetic and numeric 

characters could also be entered individually via touch points. These were used when entering location 

identifiers, altitude requests, etc. (appendix B). 

In the conventional voice-transmission condition, both pilots wore headphones with an attached 

microphone and used push-to-talk microphone keys located on the aircraft control stick. In accordance 

with normal operating procedures, pilots were required to enter the appropriate communications frequency before transmission. This was also required for display-based communications, but only to provide a communications backup should the data link fail or an emergency occur. Also in accordance with 

standard procedures, pilots were instructed to acknowlege all transmissions, whether conventional or 

data link, as quickly as possible. Pilots were instructed to comply with ATC data link instructions as they 

would with conventional voice, e.g., in accordance with existing rules and regulations. 

, 

4 
Alerting System 

In conventional voice transmissions, each communication is prefaced by the appropriate aircraft call 

sign (or ground facility) to ensure that the information reaches its intended recipient. In data link transmissions, each aircraft is addressed discretely, making the use of call signs ostensibly superfluous. However, call signs also serve to alert the aircrew to impending communications, thereby generally enhancing the speed of information transfer. Data link transmissions, in contrast, will require an artificial means 

of alerting the crew that a message is in transit. For the present study, each uplinked message was preceded by a 3-&, flashing green light mounted on the glare shield in front of each crew position. In addition, a flashing “ATC UPLINK” message was displayed on the last line of the terminal display. The pilot 

was required to acknowledge the transmission by pressing the RECVD or UNABLE touch points on the 

terminal display. Either response would immediately extinguish the alert as well as notify the ground 

system that the message had been received. The alert would continue to flash until the pilot 

acknowledged the message. The controller monitoring the data link transmissions was made aware of 

when the message was acknowledged by the pilot as this downlink transmission appeared on the simulated ATC display. 

Procedure 

Each of the eight pilots evaluated both the conventional voice and the display-based communication 

systems while serving in the copilot crew position. The pilots flew both legs of a flight between 

Los Angeles International Airport (LAX) and San Francisco International Airport (SFO). One leg of this 

round-trip flight used conventional voice transmissions and the other leg used data link display-based 

communications. Origination (LAX or SFO) of the flight was counterbalanced across pilots, as was the 

order in which the two communications systems were evaluated. 

Mor to the flight simulation test scenario, each pilot received a briefing on the proposed data link 

system. The system simulated in this study was comparable to the Mode-S system proposed by the FAA 

in ground-air-ground transmission time and in information-transmission rate. Each pilot was provided 

with part systems training on the use of the display-based communications terminal. Flight deck famil- 

’ iarization as well as full-mission training on data link system operation was provided before the test 

simulations. The simulation training was restricted to local flight in the SFO area, but included training 

in all phases of flight. 

Test Scenario 

With few exceptions, the test flight scenario replicated a scheduled air carrier flight between SFO 

and LAX. Standard instrument departures were used at both SFO and LAX. A profile descent was used 

for the SFO approach and a Standard Instrument Arrival was used for the approach into LAX. Details 

concerning the flight such as weather, runway assignments, etc., can be found in appendix C, which lists 

all ATC communications to the aircraft for both legs of the flight scenario. Communications to other air 

traffic were not simulated in the test scenario. 

5 
A few anomalies were introduced into the test scenario to compare pilot performance in operating the 

two communications systems under other than routine flight operations. In general, these operational 

anomalies also required the pilot to operate additional features of the communications terminal which 

would not normally be used. The following events were introduced for the SFO to LAX leg of the flight: 

(1) an incorrect altitude assignment which exceeded the aircraft’s maximum performance ceiling, and 

(2) an enkoute weather advisory issued for clear air turbulence within an altitude range which included 

the assigned flight level clearance. Both required pilot-initiated requests for new clearances. The LAX to 

SFO segment required the execution of a ground-initiated missed approach caused by a disabled aircraft 

on the SFO assigned runway. The missed approach required the aircraft to maintain a holding pattern at 

a nearby navigation fix for 10 min before being reissued an approach clearance. 

Measurements of pilot performance were taken throughout the flight-simulation scenario. The two 

measures of central interest were the ratings of subjective workload and the time taken for the pilot to 

acknowledge transmissions from ATC. Workload ratings were administered by the experimenter 

following takeoff/departure and approach/landing phases. For the LAX to SFO leg, ratings were also 

requested following the missed approach. The ratings were taken in periods of low task activity as soon 

as practicable following flight phase completion to minimize interference of workload administration 

with ongoing cockpit activities. 

The workload rating administered was a modified version of the NASA Task Load Index (TLX), 

details of which can be found in Hart and Shreveland (1987). Ratings for six workload dimensions are 

provided: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, and Frustration 

Level. A bipolar rating scale for overall workload is provided. Definitions of the six workload dimensions are given in appendix D. Instructions in the use of the rating scales were provided before simulation training and testing. 

Also of interest was the time taken for the pilot to acknowledge transmissions. For conventional 

voice transmissions, this is defined as the elapsed time between the end of the ground-air transmissions 

and the initiation of the pilot’s verbal response. This time was calculated from tape recordings of cockpit 

voice transmissions. Acknowledgment of a data link communication in this study was measured from 

the onset of the communications uplink alert in the cockpit to the time the pilot keyed the appropriate 

response on the communications terminal. Some increase in acknowledgment time with terminal communications was anticipated because of the combined effects of limited operating experience and the 

additional time needed to visually locate and execute the appropriate terminal response. 

Following simulation testing, pilots were pmvided the opportunity to discuss the advantages and disadvantages of the display-based communications system compared to the voice system now in use. 

Pilots were also specifically asked to identify any potential loss of information that may result from 

implementation of this communications system. 

6 
RESULTS AND DISCUSSION 

Of central interest in the comparison of conventional voice communication and the data link system 

used in this study was the time taken to acknowledge transmissions and the change, if any, in pilot 

workload introduced by display-based communications technology. 

Because of technical difficulties with recording equipment, only five of the eight pilots’ 

acknowledgment times could be analyzed. Histograms reflecting the time needed to acknowledge ATC 

communications via data link for the five pilots from which data could be collected are shown in figure 1. The range of average response times across all flight phases was from 8 to 13 sec. This time, as 

noted earlier, is measured from the time the message alert is displayed to the time the pilot keys the 

ACKNOWLEDGE touch point on the data link terminal. By comparison, the average time to respond to 

conventional transmissions averages less than 2 sec. 

The length of time to acknowledge communications via data link is of particular concern from the 

perspective of NAS system efficiency; flight deck design; and, ultimately, flight safety. Previous studies 

on data link communications also reveal slow acknowledgment times. In part, the slow response times in 

the present study can be attributed to the need for pilots to read the displayed message before 

acknowledgment. In the visual analog of conventional voice transmissions, the pilot has to read the 

message after it is delivered to the aircraft, whereas in voice communications the message is monitored 

aurally during the message transmission. Using an average adult reading speed of four words per sec 

(Carr, 1986), the average message reading time for in-flight messages (excluding ATIS) should have 

been about 2 sec. The remaining time used to acknowledge data link transmissions is attributable to 

other factors such as the time required to orient to the terminal display and, in some cases, time spent 

discussing the message content with the pilot flying (despite instructions to acknowledge transmissions 

as quickly as possible). These factors need to be examined more closely in subsequent studies, with the 

aim of significantly enhancing the efficiency of display-based communications with improved design 

and procedures. 

A second objective of this study was to assess the effect of data link communications on pilot workload. Any new system introduced into the flight deck will eventually be evaluated in terms of increasing 

or decreasing crew workload. This is particularly true of aircraft certified for two crewmembers, as the 

certification assumes a level of workload that can be adequately handled by two pilots. Many design, 

training, and procedural factors combine to affect the workload imposed on the operator of a system. 

Certainly no single study can properly address the contribution of all of these factors to the workload 

imposed by a new communications system. However, in the belief that some indices of workload would 

reveal potential problem areas with the data link system implemented in this study, workload ratings for 

both conventional and data link communications were provided by each pilot. For this study the NASA 

TLX ratings were taken five times during the round-trip flight. One rating was taken for each of the two 

takeoff/climb phases, one for each of the two approacManding phases, and one following the missed 

approach. Figure 2 shows the mean workload rating for each of the TLX categories (one category, Performance, is not shown). In virtually every category, workload ratings were slightly higher for displaybased communications than for conventional voice. However, none of these differences between the two 

7 
communications systems was found to be statistically reliable (p > 0.05). Whatever the impact of a data 

link communications system may be on other aspects of crew behavior, it did not significantly affect 

workload as measured by the TLX system. It should be noted, however, that the operations simulated in 

this study were relatively routine, with the exception of the missed approach and minor changes to 

clearances. Subsequent studies in more demanding operations are needed to fully assess the effects of 

data link operations on crew workload. 

Following completion of the simulation, all pilots were asked to identify the advantages and 

disadvantages of the data link system and to suggest methods of improvement. Pilots cited the chief 

advantages of display-based communications as being the elimination of radio chatter and the ability to 

confirm instructions from the ground either by reference to the display or to the printout. The ability to 

make requests of the ATC system without having to wait for the frequency to clear was another advantage, as was the elimination of the need to memorize or manually record information. The commonly 

cited disadvantage of data link communications was the increased head-down time that such a system 

might require. This is of particular concern in the terminal area where reprogramming of Flight Management Computers is already causing concern among these and other pilots that too little time is spent 

looking outside the cockpit for other traffic. Of the eight pilots tested, five also voiced concern over the 

potential loss of traffic information resulting from data link communications. (Note that traffic was not 

simulated in this study). Pilots often monitor the communications frequency to locate other aircraft and 

their intentions as well as to assess the possibility of, and plan for, delays or reroutings that may occur. 

This “party line” effect of common monitoring of the same radio frequency is not possible with the discrete address communications of data link. In data link communications, a particular aircraft receives 

’ messages intended for it and not for any other aircraft. While discrete address has several advantages, 

e.g., eliminating the problem of inadvertently taking clearances intended for others, the loss of potentially vital, tactical information may be a serious disadvantage. Further investigation into the value of 

frequency monitoring, the effect of its loss on operational efficiency and safety, and the potential for 

replacing the lost information by some other means is needed. 

Observations by the experimenter during the course of the simulation also revealed that other areas 

of flight deck integration will be affected by data link communications. Communication between 

crewmembers is one such area. The visual display of messages necessitates that one pilot verbalizes the 

contents to the other. This is needed even though messages are displayed for both positions, as the pilot 

flying will normally be attending to flight-path-management activities. This contrasts with conventional 

voice communications which permit frequency monitoring by all crew members. Verbalization of the 

message tended to increase the frequency and extent of conversation about the message content over 

what was observed with conventional voice transmissions. Data link communications, even with the 

addition of digitized voice for some messages, will probably increase internal cockpit communications to 

some degree, with as-yet-unknown consequences. 

Less obvious in the evaluation of data link communications is the impact of replacing human-tohuman communication with that of human-to-machine. The nonverbal elements of normal human communication, such as pacing and intonation, may convey confidence, a sense of urgency, and other information which is not generally available in display-based communications. This may result in the tendency for some individuals in this study to question clearances delivered via data link, and to delay 

acknowledgments to the “machine” to a greater extent than to conventional communications. In general. 

I 

8 
data link communications did not appear to elicit the same degree of attentiveness and promptness from 

the pilots as was compelled by voice communication in the present study. Although this is a subjective 

assessment on the part of the investigator, a similar observation has been noted by others (Hinton and 

Lohr, 1988). It may also be noted that display-based communications, which function with 

preprogrammed messages or free text entry, are much less flexible than conventional communications. 

This makes it more difficult for users to clarify and confirm message content (Parker et al., 1981). Consideration should be given to providing adequate conventional transmission capacity for this purpose in 

future NAS plans. 

CONCLUDING REMARKS 

The display-based communications system evaluated in this study resulted in substantially increased 

message acknowledgment times by pilots to ATC communications when compared to conventional 

voice transmissions. Several factors contributed to the increased response times with data link 

communications. Even though pilots were instructed to acknowledge data link messages as rapidly as 

possible, time required to visually orient to and read messages necessarily increased acknowledgment 

times. Finally, there appeared to be a general tendency to respond to data link messages with less 

urgency than to conventional voice, even though pilots were instructed to treat data link communications 

as they would conventional transmissions. It is possible that this behavior stems from a general attitude 

toward machine communications as not having the same degree of importance as communications 

between humans (pilot and controller). Further research is needed to evaluate this hypothesis, as such an 

attitude would have a significant impact on the utility of data link communications. 

Subjectively rated workload assessments of the two communications systems did not reveal statistically reliable differences. However, this finding may not be generalizable to all flight conditions (e.g., 

emergencies). Post-simulation debriefing revealed uniformly high pilot acceptance of the display- based 

communication concept. Reported advantages included the elimination of both radio chatter and the 

need to memorize or record messages. Cited disadvantages included the potential for increased headdown time and the loss of some situation awareness available from the monitoring of other aircraft 

communications. 

A number of the interface problems identified in this study can and should be addressed with 

improved design. For example, reductions in acknowledgment time can be achieved with the use of digital voice technology for time-critical, control information; although care should be taken to avoid interference with other aural alerts (e.g., TCAS). Integration of data link information into primary and secondary cockpit displays will reduce the visual orientation time, and the development of data link display 

symbology will substantially reduce the reading time (and thus head-down time) required by alphanumeric text. However, these design changes will require integration with other existing flight deck systems such as ground-proximity warnings, traffic collision avoidance, etc. Information retrieval from 

ground-based data systems will also require a more efficient interface design than was provided in the 

present study. Particular attention toward simplying the infomation retrieval process by aircrews would 

substantially enhance the utility of data link communications, particularly for aircrew access to weather 

products. 

9 
A systematic effort is needed to iden* and resolve the human-interface problems associated with 

data link communications before this system enters widespread use in the NAS. Principles of design for 

the integration of data link information systems into the flight deck of advanced aircraft, and into NAS 

operations in general, must be developed to ensure optimal ground-air-ground information transfer. A 

concerted effort to identify these issues is now in progress (Lee, Proc. FAA/NASA/Industry Workshop 

on Data Link Communications, Dec. 7-8,1988, proposed NASA CP). 

10 
APPENDIX A 

MENU ARCHITECTURE FOR DATA LINK COMMUNICATIONS SYSTEMS 

, 

10D E-S DATA LINK MENU 

UNABLE 

UNSAFE RADAR ECHOES NEAR BY 

UNSAFE IC1 NG THAT LOCATION 

REQUIRED PERFORMANCE NOT AVAILABLE 

CLEARANCE NOT CONSISTENT 

ZLEARANCEREQUEST 

PUSH BACK 

TAXI 

INITIALROUTING 

ALTITUDE REQUEST 

WILL ADVISE 

MAKINGMISSEDAPPROACH I PUBLISH ED PROCEDURE 

RETURN FOR ANOTHERAPPROACF 

ENTER HOLD FOR ### MINUT E S 

SEND 

WEATHER REQUESTS I SEQUENCEREPORTS 

UPDATE 

11 PIREPS 

FLT PLANCHANGE 
APPENDIX B 

EXAMPLES OF DATA LINK COMMUNICATIONS DISPLAY PAGES 

REQUEST FOR CLEARANCE 

<> PUSHBACK 

<> TAXI 

<> INITIAL ROUTING 

<> MODIFY FLIGHT PLAN 

<> MAKE MISSED APROACH 

<> SEND <> MAIN 

NEW ALTITUDE REQUEST 

<> REQUESTTO FLY <> 1 <> 2 <> 3 

<> 4 <> 5 <> 6 

FL LEVEL XXX <> 7 <> 8 <> 9 

-WILL ADVISEFL LEVEL XXX 

<> REQUEST TO FLY 

<> 0 

<> SEND <> CLR o BKSP <> MAIN 

12 
APPENDIX C 

GROUND-AIR DATA LINK MESSAGES 

INTL, 

MSGS No. 

5. 

10. 

20. 

22, 

24. 

26. 

28. 

30. 

32. 

34. 

36. 

38. 

40. 

42. 

44. 

SAN FRANCISCO INTL AIRPORT INFORMATION 

KILO 2045 C.U.T. VIS 7 MILES. TEMP 60 DEWPOINT 

51. WIND 270 AT 12. ALTIMETER 30.04. 

ILS RWY 28 LEFT APPROACH IN USE 

LANDING RWY 28 LEFT. DEPARTURES RWYS 

28 LEFT AND 28 RIGHT. 

CLEARED TO LOS ANGELES INTL AIRPORT 

VIA PORTE FIVE DEPARTURE AVENAL TRANS, 

AVENAL, FILLMORE 4 ARRIVAL, AVENAL TRANS, 

LOS ANGELES. MAINTAIN FL 230. SQUAWK 

7401 ON DEPARTURE. 

TAXI TO RUNWAY 28 LEFT 

CLEARED FOR TAKEOFF RUNWAY 28 LEFT 

SFO DEPARTURE 124.4 

OAK CENTER 128.35 

OAK CENTER 135.55 

CLIMB TO AND MAINTAIN FL 490 

CLIMB TO AND MAINTAIN FL 290 

PROCEED DIRECT AVENAL 

SFO WX ADVISORY. CLEAR AIR TURBULENCE 

FL 250 THRU FL 300. SMOOTH ABOVE AND 

BELOW. 

CLIMB TO AND MAINTAIN FL 330. 

LAX CENTER 135.30 

CLEARED TO LAX VIA FIM4 ARRIVAL 

DESCEND AT PILOTS DISCRETION 

CROSS FIM AT 15,000 AND 250 KTS 

LAX ALTIMETER 30.00. 

LAX CENTER 135.5 

13 
APPENDIX C (Continued) 

47. 

48. 

52. 

56. 

60. 

64. 

66. 

68. 

72. 

76. 

ONTARIO INTL AIRPORT INFORMATION 

WHISKEY. 25,000 THIN BROKEN 

VIS 10 MILES. TEMP 68 DEWPOINT 60. 

LAX APPROACH 124.5 

DESCEND AND MAINTAIN 10,000 

DEPART SMO HEADING 070 

RADAR VECTORS FOR ILS 24 LEFT APPROACH. 

REDUCE SPEED TO 200 KTS x 

DESCEND AND MAINTAIN 3.000 

TURN RIGHT HEADING 21 0 

DESCEND AND MAINTAIN 2,200 

CLEARED FOR THE ILS RWY 24 LEFT 

LAX TOWER 133.9 

CLEARED TO LAND Rwy 24 LEFT 

TURN LEFT NEXT TAXWAY 

LAX GROUND 121.65 

S ANGm INTL TO SAN FRANCISCO INTL 

MSGS No. 

80. TAXI TO 24 LEFT VIA UNIFORM AND 33-U 

CLEARANCE AVAILABLE ON REQUEST. 

8 0 5. LOS ANGELES INTL AIRPORT INFORMATION 

OSCAR. VISIBILITY 3 MILES IN HAZE AND SMOKE 

TEMP 61. DEWPOINT 54. WIND 270 AT 14. 

ALTIMETER 30.1 0. ILS APPROACHES RWYS 

24 LEFT AND 24 RIGHT. DEPARTURES RWYS 25 LEFT 

AND 25 RIGHT. 

81 0. CLEARED TO SAN FRANCISCO INTL AIRPORT 

VIA GORMAN SIX DEPARTURE, AVENAL TRANS, 

AVENAL DIRECT BIG SUR. BIG SUR PROFILE 

DESCENT SAN FRANCISCO. MAINTAIN 3,000. 

EXPECT FL 300 10 MIN AFTER DEPARTURE. 

SQUAWK 4701 ON DEPARTURE. 

DEPARTURE FREQUENCY IS 125.2. 

820. LAX GROUND 121.8 

8 2 4. TAXI TO RWY 25 LEFT 

14 
APPENDIX C (Continued) 

828. LAX TOWER 118.9 

832. 

836. 

840. 

844. 

848. 

852. 

856. 

858. 

860. 

868. 

872. 

874. 

876. 

880. 

888. 

892. 

CLEAREDFORTAKEOFFRWY25LEFT 

LAX DEPARTURE 125.2 

MAINTAIN HEADING 250 

RADAR VECTORS FOR VlU 

PROCEED DIRECT VENTURA 

CLIMB AND MAINTAIN FL 230 

LAX CENTER 135.5 

EXPEDITE THROUGH FL 190 

LAX CENTER 125.65 

CLIMB TO FL 300 

CLEARED TO SFO VIA BIG SUR PROFILE 

DESCENT. DESCEND AT PILOTS DISCRETION. 

MAINTAIN FL 230. 

OAK CENTER 134.55 

SAN JOSE INTL AIRPORT INFORMATION ALPHA 

2245 C.U.T. CEILING MEASURED 600 OVC 

VIS 5 MILES. TEMP 63 DEWPOINT 57. 

WIND 210 AT 12. ALTIMETER 29.98. 

APPROACH IN USE ILS RWY 30 LEFT 

DEPARTURES 30 LEFT. CAUTION FOR A CRANE 

1 MILE SOUTHWEST, 225 FT MSL. 

SAN FRANCISCO INTL AIRPORT INFORMATK)(J 

MIKE. 2245 C.U.T. CEILING MEASURED 300 OVC 

VIS 1 MILE IN FOG. TEMP 53 DEWPOINT 53 

WIND 280 AT 5. ALTIMETER 29.94 

ILS APPROACH RWYS 28 LEFT AND 28 RIGHT 

DEPARTURES RWYS 28 LEFT AND 28 RIGHT 

OAK CENTER 128.35 

CROSS BIG SUR AT 18000 

SFO ALTIMETER 30.1 5 

BAY APPROACH 123.85 

REDUCE SPEED TO 230 KTS 

15 
APPENDIX C (Concluded) 

8 9 6. 1 0 MILES FROM OUTER MARKER 

TURN LEFT HEADING 31 0 

MAINTAIN 2000 UNTIL ESTABLISHED 

ON LOCALIZER 

91 4. DESCEND TO AND MAINTAIN 3000 

9 1 8. TURN LEFT HEADING 310 

INTERCEPT LOCALIZER FOR RWY28 LEFT 

922. CLEARED FOR 11s MY28 LEFTAPPROACH 

926. SFO TOWER 120.5 

930. GOAROUND 

DISABLED AIRCRAFT ON RUNWAY 

93 2. MAINTAIN PRESENT HEADING 

CLIMB AND MAINTAIN 3000 

CONTACT BAY DEPARTURE ON 124.4 

9 3 6. TURN LEFT HEADING 180 

CLIMB TO AND MAINTAIN 4000 

94 0. CLEARED TO WOODSIDE VOR VIA PRESENT 

POSITION DIRECT. MAINTAIN 4000. 

HOLDsouMOFwooDslDEON~SIDE141 

RADIAL LEFT TURNS. EXPECT APPROACH IN 10 MIN. 

944. FLY HEADING 350 FOR VECTORS TO 28 LEFT FINAL APPROACH COURSE 

948. 10MlLES FROMOUTER MARKER 

TURN LEFT HEADING 31 0 

MAINTAIN 2000 UNTIL ESTABLISHED 

ONLocAuaER 

9 5 2. CLEARED FOR 11s RWY 28 LEFT APPWACH 

956. SFOTOWER 120.5 

960. CLEARED TO LAND Rwy 28 LEFT 

964. TURN LEFT NEXTTAXIWAY 

SFO GROUND 121.8 

16 
APPENDIX D 

Title 

MENTAL 

DEMAND 

PHYSICAL 

DEMAND 

TEMPORAL 

DEMAND 

PERFORMANCE 

EFFORT 

FRUSTRATION 

LEVEL 

WORKLOAD RATING SCALE DEFINITIONS 

Low/High 

Low/H ig h 

Low/H ig h 

GoodlPoor 

Low/High 

Low/High 

DescriDtians 

How much mental and perceptual 

activity was required (e.g. 

thinking, deciding, calculating, 

remembering, looking, searching, 

etc.)? Was the task easy or 

demanding, simple or complex, 

exacting or forgiving? 

How much physical activity was 

was required (e.g. pushing, pulling, 

turning, controlling, activating, etc.)? 

Was the task easy or demanding, 

slow or brisk, slack or strenuous, 

restful or laborious? 

How much time pressure did you 

feel due to the rate or pace at which 

the tasks or task elements occurred? 

Was the pace sbw and leisurely or 

rapid and frantic? 

How successful do you think you 

were in accomplishing the goals of 

the task set by the experimenter (or 

yourself) How satisfied were you 

with your performance in 

accomplishing these goals? 

How hard did you have to work 

(mentally and physically) to 

accomplish your level of 

performance? 

How insecure, discouraged, irritated, 

stressed and annoyed versus 

secure, gratified, content, relaxed 

and complacent did you feel during 

the task? 

17 
REFERENCES 

Billings, C. E.; and Cheaney, E. S.: Information Transfer Problems in the Aviation System. NASA 

TP-1875, 1981. 

Carr, T. H.: Perceiving Visual Language. Handbook of Perception and Human Performance, Vol. 2. 

K.R. Boff, L. Kaufman, J.P. Thomas, eds., John Wiley & Sons, 1986. 

Diehl, J. M.: Human Factors Experiments for Data Link. FAA-RD-75-160,1975. 

Hart, S. G.; and Shreveland, L. E.: Development of NASA-TLX (Task Load Index): Results of 

Empirical and Theoretical Research. Human Mental Workload, P.A. Hancock and N. Meschkati, 

eds., Amsterdam, The Netherlands, 1987. 

Hinton, D. A.; and Lohr, G. W.: Simulator Investigation of Digital Data-Link ATC Communications in a 

Single-Pilot Operation. NASA TP-2837, 1988. 

Lee, A. T.; and Lozito, S.: Air-Ground Information Transfer Problems in the National Airspace System. 

Proceedings of the Fifth Symposium on Aviation Psychology, Columbus, OH, April 17-20,1989. 

Parker, J. F.; Duffy, J. W.; and Christensen, D. G.: A Flight Investigation of Simulated Data Link Communications During Single-Pilot IFR Flight. Volume I: Experimental Design and Initial Tests. 

NASA CR-3461,1981. 

Parker, J. F.; and Duffy, J. W.: A Flight Investigation of Simulated Data Link Communications During 

Single-Pilot IFR Flight. Volume 11: Flight Evaluations. NASA CR-3653, 1982. 

Sexton, G.: Pilot’s Desk Flight Station. Fkceedings of the Second Symposium on Aviation Psychology, 

Columbus, OH, April 25-28,1983. 

Waller, M. C.; and Lohr, G. W.: A Piloted Simulation Study of Data Link ATC Message Exchange. 

NASA Technical Paper 2859, February, 1989. 

Uckermann, R.; and Radke, H.: Evaluation of an Airborne Terminal for Digital Data Link in Aviation. 

DFVLR-FB 83-05, 1983. 

18 
T T l- T 

TAXI TAKEOFF CRUISE DESCENT APPROACH MISSAPPR 

Figure 1.- Mean acknowledgment time to data link messages as a function of flight phase (N = 5; 

CV: Mean time to acknowledge conventional voice transmissions). 

19 
100 

(3 80 z 

F 

2 60 

100 c!J 

z 

$ 80 

n 

8 

8 

3 20 

2 40 

- 

- 

0 DISPLAY 

VOICE 

bl TAKEOFF 

n I 

LANDING MISS APPR 

EFFORT 

I n 

LANDING TAKEOFF MISS APPR 

I TEMPORAL 

Y 

40 3 

20 

TAKEOFF LANDING MISS APPR 

PHYSICAL 

n 

FRUSTRATION 

0 DISPLAY 

VOICE 

TAKEOFF LANDING MISS APPR 

MENTAL 

0 DISPLAY 

VOICE 

TAKEOFF LANDING MISS APPR 

OVERALL 

Figure 2.- Pilot workload ratings for voice and data link communications systems (N = 8 pilots). 

20 
-- 

. 

I 

17. Key Words (Suggested by Author(s1) 

Data link 

Advanced transports 

Human factors 

National Airspace System 

Report Documentation Page 

18. Distribution Statement 

Unclassified-Unlimited 

Subject Category - 54 

1. Report No. 2. Government Accemion No. 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 

Unclassified Unclassified 

NASA TM-102187 

4. Title and Subtitle 

21. No. of pages 22. Price 

22 A02 

Display-Based Communications for Advanced Transport 

Aircraft 

7. Authorls) 

Alfred T. Lee 

9. Performing Organization Name and Address 

Ames Research Center 

Moffett Field, CA 94035 

2. Sponsoring Agency Name and Address 

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

5. Supplementary Notes 

3. Recipient's Catalog No. 

5. Report Date 

May 1989 

6. Performing Organization Code 

8. Performing Organization Report No. 

A-89118 

10. Work Unit No. 

505-67-21 

11. Contract or Grant No. 

13. Type of Report and Period Covered 

Technical Memorandum 

14. Sponsoring Agency Code 

Point of Contact: Alfred T. Lee, Ames Research Center, MS 239-1, Moffett Field, CA 94035 

(415) 694-6908 or FI'S 464-6908 

~ 

6. Abstract 

The next generation of civil transport aircraft will depend increasingly upon ground-air-ground 

and satellite data link for information critical to safe and efficient air transportation. This paper 

reviews previous studies which have examined the concept of display-based communications in 

addition to, or in lieu of, conventional voice transmissions. A full-mission flight simulation comparing voice and display-based communication modes in an advanced transport aircraft is also 

described. The results of this study indicate that a display-based mode of information transfer does 

not result in significantly increased aircrew workload, but does result in substantially increased message acknowledgment times when compared to conventional voice transmissions. User acceptance of 

the display-based communication system was generally high, replicating the findings of previous 

studies. However, most pilots tested expressed concern over the potential loss of information 

available from frequency monitoring which might result from the introduction of discrete address 

communications. Concern was expressed by some pilots for the reduced time available to search for 

conflicting traffic when they were using the communications display system. The implications of the 

findings for the design of display-based communications are discussed. 

I I I 

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