Next Generation Air-Ground Communication (NEXCOM)
Updated:10:59 AM May 03, 2012
The 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 is a time-division, multiple access system that provides increased channel capacity and will be capable of transmitting both voice and data. The system has several design characteristics that may affect its usability. The quality of the digitized voice and the longer voice throughput delay were the primary user concerns. The VDL3 system will also have special features such as controller override, antiblocking, and a transmit status indicator (TSI). Although designed to improve the overall system, the features could produce unexpected effects for some users on the communications network. The Human Factors Branch has conducted a series of studies about the NEXCOM characteristics to determine whether controllers and pilots can effectively use the system.
The first two studies addressed the intelligibility of digitized voice compared to analog communications in loud ambient noise conditions. LaDue, Sollenberger, Belanger, & Heinze (1997) conducted a field study using recorded communications. The second study (Sollenberger, LaDue, Carver, & Heinze, 1997) was a high fidelity, human-in-the-loop simulation comparing analog and digital radio communications, but without the other VDL3 characteristics. The results indicated that the digital voice quality was acceptable. The third study (Sollenberger, McAnulty, & Kerns, 2003) was a high fidelity, human-in-the-loop simulation to evaluate the effects of the VDL3 system characteristics, especially its increased throughput delay, on air traffic controller performance and workload. The results indicated that the VDL3 system with a 350 ms throughput delay was highly acceptable to controllers, and that the more stringent and costly 250 ms specification was unnecessary.
The fourth study (Zingale, McAnulty, & Kerns, 2003) was a cockpit simulation [link to cockpit simulation capability] to assess VDL3 system effectiveness and pilot workload in comparison to analog communications. The results showed that users accessed the channel similarly with both radios, but the digital system resulted in a higher percentage of successful transmissions. The participants almost always rated the digital system as being equal to or better than the analog system for air-ground communication tasks. The basic system features were also rated highly, except that some pilots had difficulty hearing the TSI. Subsequently, we used our audiometric booth to evaluate the detectability of TSIs that differed in frequency, amplitude, and periodicity to the current specification. We then evaluated the intelligibility of incoming voice messages when the alternative TSIs were active. On the basis of the test results, we recommended that the program office revise the specifications for the TSI.
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