Air Traffic Control:

FAA's Transition of Communications System to Digital Technology

IMTEC-91-77FS: Published: Sep 26, 1991. Publicly Released: Oct 30, 1991.

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Pursuant to a congressional request, GAO reviewed the status of the Federal Aviation Administration's (FAA) plans for the transition of the Radio Communications Link (RCL) system, an integrated voice and radar data transmission system that is the largest of three components in the FAA program to replace and expand the existing Radar Microwave Link communication system, from analog to digital technology.

GAO found that: (1) digital technology has advanced while analog technology has become obsolete, and cost differences between the two technologies for long-distance communications have narrowed, making digital technology more attractive from a cost viewpoint; (2) in August 1991, FAA began installing equipment on the RCL system to enable the transmission of digital data over digital communications lines, while maintaining its current analog-based RCL system; (3) several studies performed for FAA in 1988 and 1989 concluded that digital technology would be needed to meet future FAA air traffic control requirements, while offering performance improvements with reduced operating costs; (4) FAA decided to convert its system gradually because it wanted to realize a return of the substantial investment already made in analog technology, believed the analog RCL system would provide enough capacity to meet the communications work load through the end of the century, and wanted to further study when to convert to digital technology; and (5) to assist in the transition planning, FAA initiated two contractor studies to design a future digital communications architecture and determine when to fully change FAA interfacility communications system, including the RCL system, to digital technology.