FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute
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AVIATION MEDICINE REPORTS

Report No: DOT/FAA/AM-01/8

Title and Subtitle: Data-linked pilot reply time on controller workload and communication in a simulated terminal option

Report Date: May 2001

Authors: Prinzo, O.V.

Abstract: This report describes an analysis of air traffic control communication and workload in a simulated terminal radar approach control environment. The objective of this study was to investigate how pilot-to-controller data-link acknowledgment time might affect controller-perceived workload and operational communication. Eight controllers provided air traffic services to simulated arrival aircraft during a moderate-traffic density simulation in which voice radio and data link communications were available. The effect of a delay in downlinked pilot acknowledgment time to controller uplinked messages was the primary variable of interest.

Each controller completed the same scenario twice, with the order of presentation counterbalanced. That is, for the first simulation, half the controllers received immediate responses to their data link messages while the other half received pilot acknowledgment time delayed by about 11 seconds.

The primary finding was a general, albeit not statistically significant, tendency among controllers towards an increase in subjective workload overall and on individual dimensions of the NASA Task Load Index when the simulation environment supported mixed, rather than immediate pilot responses. The analysis performed on communication measures revealed that controller workload was affected by the communications capability onboard the aircraft but not ghost pilot response type (immediate, delayed). Transmissions to data link-equipped aircraft took longer to complete and contained longer pauses than transmissions to non-data linked aircraft. The mode of communications selected by controllers also influenced workload but ghost pilot response type did not.

When controllers used data link, their transmissions took nearly 2 seconds longer to complete than comparable messages sent by voice. When compared with voice radio messages, controllers took longer to formulate and transmit messages over a data link-communications system, but their messages were more accurate and contained fewer message elements. This finding was replicated when messages with courtesies, salutations, and those involved in the initial contact services were removed. Often, the data-link transmissions that contained longer pauses resulted from deliberate actions on the part of the controllers.

Longer latencies did not result in a loss of efficiency but reflected innovations on the part of the controllers to optimize performance. For example, by placing data-link messages in a pending status, controllers would communicate with a non-data-link-equipped aircraft. When the data link-equipped aircraft arrived at a transition-point along their filed flight plan (generally approaching a hand-off point or transition altitude or fix), controllers uplinked their already composed messages to those aircraft.

Key Words: Air Traffic Control Communication, Data Link

No. of Pages: 21