Abstract: A collision avoidance system using on-board B-CAS equipment having an object to minimize interference with the ground SSR stations and to effect precise tracking or distance-altitude measurement when necessary. Normally passive surveillance is made to detect the presence of other aircraft in the B-CAS range. Active surveillance is added when required. In the active surveillance mode, initiated on locating an intruder aircraft, the power and interrogation signal are varied when the intruder aircraft becomes a threat aircraft to minimize interference with the ground SSR stations and aircraft outside the threat zone while maintaining accuracy of detection and tracking of the threat aircraft at a high level.

Abstract: A collision avoidance system for aircraft using an on-board beacon interrogator. If altitude information is not included in a response signal from a transponder of an other aircraft or the response signal is garbled because a plurality of other aircraft are responding to the same interrogation signal, the system automatically switches to a beacon based proximity warning system and indicates the distance or other indication to the detected aircraft.