Tuesday, March 04, 2008

FAA History Lesson -- March 4



From the FAA Historical Chronology, 1926-1996...

”Mar 4, 1976: FAA announced a contract for the development of three engineering model Discrete Address Beacon System (DABS) ground sensors and 30 compatible transponders. This new advanced radar beacon system was designed to eventually replace ATCRBS, the existing air traffic control radar beacon system (see Dec 27, 1963). The chief advantage of DABS was its ability to interrogate and receive a transponder reply from a specific aircraft rather than from all aircraft in the zone of coverage. This would help eliminate the problem of overlapping and garbling of transponder replies from aircraft flying in close proximity to one another. Since DABS would address aircraft on an individual basis, it would also provide a vehicle for automatic communications between aircraft and the ground. This data link capability was seen as the basis for future implementation of a ground-based collision avoidance system called Intermittent Positive Control (IPC), later designated the Automatic Traffic Advisory and Resolution System (ATARS). (See Mar 1976.) “

I wish every reporter that will type the word “NexGen” in the next decade could read and understand this entry. Thirty two years ago the FAA was talking about NexGen. There are numerous good ideas on improving the air traffic control system. Getting them implemented is a different matter altogether.

See that “data link capability” above ? That is the key to improving the efficiency of air traffic control. Not the efficiency of runways -- I’ve already covered that subject -- but the number of airplanes a controller can handle. Right now, the limiting factor is the number of airplanes a controller can talk to on the radio. The more a controller has to talk, the less airplanes he can work.

For those that are scratching their heads, saying they’ve never heard of “DABS” -- it’s Mode S.

From the FAA Historical Chronology, 1926-1996...

”Jun 23, 1981: Administrator Helms announced FAA's decision to adopt the Threat Alert and Collision Avoidance System, soon renamed the Traffic Alert and Collision Avoidance System (TCAS). The TCAS system was an evolutionary improvement of the Beacon Collision Avoidance System (BCAS) that the agency had been developing (see Mar 1976). Like BCAS, TCAS would work in conjunction with the Air Traffic Control Radar Beacon System (ATCRBS) transponder already in wide use. It would also be compatible with the next-generation transponder, originally designated the Discrete Address Beacon System (DABS) and later known as Mode S (see Dec 27, 1978, and Oct 5, 1984).

Two types of the new collision avoidance system were planned. TCAS I, intended for general aviation use, would in its basic form simply alert the pilot to the proximity of another aircraft carrying TCAS I or a conventional ATCRBS transponder. More expensive TCAS I versions would have some ability to provide certain data on the altitude and/or "o'clock" position of threat aircraft. TCAS II would provide more sophisticated advisories, including data on range and bearing of transponder-equipped aircraft. When the transponder aboard the threat aircraft had altitude-reporting capability, TCAS II's advisories would also include altitude data. In the case of two aircraft equipped with TCAS II, coordinated advisories would be provided. TCAS II would suggest vertical escape manuevers. If feasible, the system might be enhanced to include both vertical and horizontal escape manuevers, a version later designated TCAS III. TCAS was expected to overcome a fundamental limitation of BCAS by its ability to operate effectively even in the highest air traffic densities. This modified the need for a new ground-based collision avoidance system, and led to discontinuance of the Automatic Traffic Advisory and Resolution System (ATARS) project, originally known as Intermittent Positive Control (see Mar 4, 1976). “


By the way...does anybody know what happened to TCAS III (27 years later) ? That is two years longer than my entire career with the FAA.

Don Brown
March 4, 2008

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