A passive aircraft Traffic alert and Collision Avoidance Device (TCAD) is based on sensing and responding to transponder replies of other aircraft to SSR interrogations. In order to avoid masking other aircraft replies by the host transponder TCAD repeatedly and randomly suppresses the host transponder...http://www.google.de/patents/US5157615?utm_source=gb-gplus-sharePatent US5157615 - Aircraft traffic alert and collision avoidance device
