The Effect of Voice Communications Latency

Full Text: PDF icon Pdf (0.47 MB)
Document Number:
Publication Date:
Authors: Karol Kerns
D. Michael McAnulty
Carolina Zingale, PhD.

Zingale, C. M., McAnulty, D. M., & Kerns, K. (2003). The effect of voice communications latency in high density, communications-intensive airspace phase II: Flight deck perspective and comparison of analog and digital Systems (DOT/FAA/CT-TN04/02). Atlantic City International Airport, NJ: Federal Aviation Administration William J. Hughes Technical Center.


The FAA Next Generation Air-Ground Communications (NEXCOM) program plans to replace the aging analog air traffic communications system with a Very High Frequency (VHF) Digital Link Mode 3 (VDL3) system. VDL3 provides increased channel capacity, can transmit both voice and data, and compensates for known limitations in the analog system through features such as controller override, antiblocking, and a transmit status indicator. The system also virtually eliminates “step-ons.” However, VDL3 will have a longer voice throughput delay (up to 350 ms) than the analog system (approximately 70 ms). This report describes the second high fidelity, human-in-the-loop simulation study of VDL3 system performance and operational acceptability. The first study evaluated VDL3 with air traffic controllers. We conducted the current study to validate the findings of the first study with pilots, to compare analog communications to those using VDL3, and to assess analog and VDL3 communications under routine conditions and under adverse weather conditions that further increased demand for the channel. Fourteen airline pilots participated in the study using two realistic flight deck simulators. VDL3 allowed more successful transmissions to be made. Most other communications characteristics did not differ between the radio systems. The effects of adverse weather were similar for both systems. The participants were highly positive in their evaluations of VDL3. They rated the operational acceptability of VDL3 higher than analog, and they nearly always rated the digital system as equal to or better than analog for completing communication tasks. Overall, the results indicate that VDL3 is an acceptable communications system for pilots.