Air Safety

Pursuant to a congressional request, GAO reviewed the Federal Aviation Administration's (FAA) actions in the development of mid-air collision avoidance back-up systems, specifically: (1) whether a commercial air-based collision avoidance system has been available since 1975; (2) the difference between the current avoidance system and its predecessor; (3) the projected date for commercial availability of the current FAA avoidance system; and (4) a comparison of the costs and effectiveness of a commercial system versus the FAA system.

GAO found that, by the 1970's, private industry had developed several Airborne Collision Avoidance Systems (ACAS) that would have required additional work to correct technical and operational problems if they were to be implemented nationally. FAA then developed the Beacon Collision Avoidance System (BCAS), which used the existing Air Traffic Control Radar Beacon System (ATCRBS) equipment and was, therefore, less costly and more effective than ACAS. The Traffic Alert and Collision Avoidance System (TCAS), a more advanced and improved version of BCAS, was introduced in 1981. TCAS operates more effectively than BCAS in denser air traffic and its design includes a lower-cost, less-capable model for general aviation, unlike BCAS, which was designed primarily for air carrier use. There are three TCAS models, one designed for general aviation aircraft use and two designed for passenger aircraft use. No date has been set for the availability of the TCAS model designed for general aviation aircraft. However, the models designed for passenger aircraft are expected to be available around 1990. The estimated costs of TCAS and ACAS vary. Available figures suggest that ACAS would be less expensive; however, ACAS are completely different systems than TCAS and, therefore, the costs of the two types of systems cannot be meaningfully compared. GAO also found that no studies were available comparing the effectiveness of ACAS and TCAS.