Automatic Independent Surveillance – Privacy (AIS-P) is a data packet protocol for the TailLight system of aircraft Traffic Collision Avoidance System (TCAS), wherein a single Mode S 64 microsecond message is transmitted by an aircraft ATCRBS or Mode S transponder, and received by aircraft and Air Traffic Control on the ground.
AIS-P and ADS-B are competing protocols for aircraft based surveillance of traffic, a replacement technology for Mode S radar and TCAS.
The TailLight, which is offered as a complimentary feature in General Aviation ATCRBS transponders like the AT-155, utilizes the AIS-P protocol to effectively deliver the advertised collision avoidance benefits of ADS-B in both airport terminal and en route airspace.
One packet encodes latitude and longitude, altitude, direction, and speed (full position and velocity), handles error detection and recovery, along with channel use arbitration, in the AIS-P protocol.
Additionally, one of the requirements satisfied by the AIS-P protocol is that a missile with an ADS-B type target homer aimed at the unnamed aircraft alone in the sky would miss.