Air Transport World

TCAS at the turning point. (Traffic Alert and Collision Avoidance System)

Congress has mandated that 20% of fleets using U.S. airspace be equipped with collision-avoidance systems by year-end. By Lester Reingold.

"In time, a [collision-avoidance system] will be used by all aircraft that share airspace, regardless of when or where they fly." That was the forecast of Frank C. White, manager of communications data processing for ATA. Writing in 1967, White probably could not have guessed how much time really would be needed. [F]light evaluation of airborne collision-avoidance systems," he also predicted, would commence during the first quarter of 1969. Two decades later, flight testing was still being conducted.

The quest for collision-avoidance technology actually began in 1955, when ATA issued a request for proposals. It was not until 1981 that the U.S. FAA focused the research on the current format, an air-to-air system known as Traffic Alert and Collision Avoidance System (TCAS). But after collaborative efforts that spanned 35 years involving FAA, avionics manufacturers and the eventual system users, this year will mark the turning point; TCAS becomes operational.

As Thomas Williamson, electronics engineer in FAA's TCAS program, pointed out, midair collisions are "almost guaranteed to be catastrophic." The black boxes that are slated for installation on commercial aircraft later this year constitute a system that meets all the performance criteria established by FAA, which are:

* Be compatible with the current ATC system and serve as a logical extension of that system.

* Maintain effectiveness even in dense traffic.

* Require no ground-based equipment.

* Be able to accommodate the needs of various classes of airspace users.

Three versions of TCAS are planned. In each, the on-board system can only "see" aircraft that are equipped with transponders. Also, the system can provide altitude information only if those transponders are Mode C or Mode S, the altitude-encoding varieties. Congress has directed FAA to issue a rule requiring these two modes on all aircraft operating in terminal-control areas and airport radar service areas as well as above 1 0,000 ft.

TCAS I will be strictly a warning device, providing the pilot with "traffic advisories" disclosing the range, approximate bearing and altitude of traffic within four nm. …

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