Traffic Collision Avoidande System

The Traffic alert and Collision Avoidance System (or TCAS ) - alarm system of traffic and avoidance of collision - is an implementation of the Airborne Collision Avoidance System (system of avoidance of collision in flight) whose ICAO imposed the installation on all the aircraft of more than 5.700kg or who transport more than 19 passengers, with for objective the reduction of the number of boardings.

On the aircraft provided with a Knell cockpit (digital screens), the TCAS can be integrated in ND (Navigation Display). On the knells older cockpits and the aircraft equipped with mechanical instruments, the instantaneous vertical speedometer (IVSI) is replaced by a similar electronic instrument, integrating the TCAS.

The TCAS posts all the other planes equipped with TCAS (or in any case with a transpodor mode C, in a ray defined by the pilot, between 2.5 and approximately 40 nautical miles. If a plane appears and represents a potential danger of collision, a notification of traffic is emitted by the Advisory Traffic (TA). This last informs the pilot who another plane is in the vicinity, by announcing " vocally; traffic, traffic" , but does not suggest an operation of avoidance. Nevertheless, if the situation worsens and the collision seems imminent, an audio message and a visual alarm are produced by the Advisory Resolution (RA), indicating the plane concerned and announcing the action to be carried out by the pilot, namely to maintain the trajectory current, to assemble, descend or supervise vertical speed. The system is conceived so that the TCAS of the other plane advises another operation (it would not be very interesting that the two planes are avoided while assembling both). Very often, the TCAS indicates to a plane to go up and the other to go down, which increases considerably separation between the two apparatuses. When alarm is finished, the system announces " clear off conflict" (more in conflict). The TCAS is an interrogative system, which questions the close planes on frequency 1030 MHz. The plane answers then on frequency 1090 MHz. The avoidance of collision can also be passive, such as for example the PCAS or Portable Collision Avoidance System (portable system of avoidance of collision), which does nothing but listen to the answers of the other apparatuses, without emitting. This portable system is typically used in the General aviation (mainly business aircrafts).

History

Although research in the systems of avoidance of collision in flight started in the years 1950, which decided the Federal Administration of the United States Air Force (Federal Aviation Administration or FAA) is a succession of collisions in flight implying of the airliners and causing many deaths. Among these tragic accidents, one notes the Vol United Airlines 718, victim of a collision in flight near the Large Canyon in 1956 and the Vol PSA 182, a Boeing 727 which struck a Cessna 182 in 1978.

TCAS II

Description

Development

Although the system causes sometimes false alarms, the pilots have now the strict instruction to regard all messages TCAS as real alarms requiring an immediate intervention. The regulation of the federal Administration of the United States Air Force and the authorities of the majority of the other countries specify that in the event of difference between the instructions of the TCAS RA and the Contrôle of the air traffic (ATC), the TCAS RA always has the priority. This is due to a precedent where a plane had followed the TCAS and the other air control, on July 1st, 2002 above the lake of Constancy (Germany). A Tupolev You-154 of the company Bashkirian Airlines and a Boeing 757 -200 cargo liner of DHL were struck in flight whereas they were both equipped with a TCAS. The pilot of Tupolev followed the instructions of the air-traffic controller, whereas Boeing, on another frequency, followed TCAS
The crash landing also was the subject of a documentary film in the series dangers in the sky under the title Vol Btc 2937, Mortal Croisement . It was learned later that the Danish air-traffic controller, at the origin of the instruction, was assassinated in his residence by Russian who lost his wife and his 2 children in the tragedy. See the article Flight 2937 Bashkirian Airlines.

Legal situation in the world

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