- Aircraft collision avoidance systems
aircraftcan use several types of collision avoidance systems to prevent unintentional contact with other aircraft, obstacles, or the ground:
Radarcan detect the relative location of other aircraft, and has been in military use since World War II, when it was introduced to help night fighters (such as the de Havilland Mosquitoand Messerschmitt Bf 110) locate bombers. While larger civil aircraft carry weather radar, sensitive anti-collision radar is rare in non-military aircraft.
* a Traffic alert and Collision Avoidance System (TCAS), which actively interrogates the
transponders of other aircraft and negotiates collision-avoidance tactics with them in case of a threat. TCAS systems are relatively expensive, and tend to appear only on larger aircraft. They are effective in avoiding collisions only with other aircraft that are equipped with functioning transponders with altitude reporting.
* use. PCAS systems do not actively interrogate the transponders of other aircraft, but listen passively to responses from other interrogations. PCAS is subject to the same limitations as TCAS, but also is ineffective if there is not at least one system (such as air traffic control or a TCAS-equipped aircraft) interrogating another aircraft's transponder.
Ground proximity warning system(GPWS), or "Ground collision warning system" (GCWS), which uses a radar altimeterto detect proximity to the ground or unusual descent rates. GPWS is common on civil airliners and larger general aviationaircraft.
Terrain awareness and warning system(TAWS) uses a digital terrain map, together with position information from a navigation system such as GPS, to predict whether the aircraft's current flight path could put it in conflict with obstacles such as mountains or high towers, that would not be detected by GPWS (which uses the ground elevation directly beneath the aircraft).
Synthetic visionprovides pilots with a computer-generated simulation of their outside environment for use in low or zero-visibility situations.
Large, sophisticated aircraft may use several or all of these systems, while a small general aviation aircraft might have only PCAS, or no collision-avoidance system at all (other than the pilot's situational awareness).
Air traffic control
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