Human Factors Evaluation of a Digital Communications System

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None; published by the AIAA/IEEE
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Authors: Karol Kerns
Michael McAnulty
Carolina Zingale, PhD.

Zingale, C. M., McAnulty, D. M., & Kerns, K. (2005). Human factors evaluation of a digital, air-ground communications system. In Proceedings of the 24th AIAA/IEEE Digital Avionics Systems Conference(pp. 5.B.5.1-9). Piscataway, NJ: IEEE.


The Federal Aviation Administration (FAA) Next Generation Air-Ground Communications (NEXCOM) program has been developing a Very High Frequency (VHF) Digital Link Mode 3 (VDL3) system to replace the aging analog air traffic communications system. VDL3 provides increased channel capacity and is capable of transmitting both voice and data. VDL3 also compensates for known limitations in the analog system by virtually eliminating “step-ons” with an antiblocking feature, enabling controller override, and providing a transmit status indicator (TSI) to indicate if the channel is occupied.

VDL3 is also expected to have a longer voice throughput delay (up to 350 ms) than the existing analog system (approximately 70 ms), which could potentially disrupt the communications flow. The delay and the acceptability of the new features were previously evaluated in a high-fidelity human-in the- loop simulation with air traffic control specialists (ATCSs) [1]. That study found that a system with a 350 ms system delay and the additional features was acceptable to controllers and did not adversely affect performance or workload. This report summarizes the second, high fidelity, human-in-the-loop simulation of VDL3 system performance and operational acceptability from the flight deck perspective. The objectives of this study were to validate the findings of the earlier simulation with pilots, to compare data obtained under analog communications to those obtained using a digital system simulating VDL3, and to assess analog and VDL3 communications under routine conditions and adverse weather conditions that further increased demand for access to the channel.

Fourteen airline pilots participated in the study using two realistic flight deck simulators. The results showed that the participants attempted to access the channel similarly with either radio system, but that the digital system allowed more successful transmissions to be made. Most other communications characteristics did not differ between the two systems. The effects of adverse weather were similar for both systems. The participants rated the operational acceptability of the digital system higher than the analog system, and nearly always rated the digital system as equal to or better than the analog system for completing communication tasks. The participants rated the antiblocking, controller override, and TSI features as highly useful. However, ratings of some aspects of the TSI were variable, indicating that improvements may be needed. In a separate effort, a group of human factors specialists evaluated alternative implementations of the TSI and made recommendations for modifications. Overall, the results indicated that VDL3, with a 350 ms voice throughput delay and enhanced system features, is an acceptable communications system for pilots.