ABSTRACT
The traffic alert and collision avoidance system (TCAS) provides a solution to the problem of reducing the risk of midair collisions between aircraft. The TCAS concept makes use of the radar beacon transponders carried by aircraft for ground Air Traffic Control purposes and provides no protection against aircraft that do not have an operating transponder. TCAS II consists of the Mode S/TCAS control panel, the Mode S transponder, the TCAS computer, antennas, traffic and resolution advisory displays, and an aural annunciator. TCAS listens for the broadcast transmission (squitters), which is generated once per second by the Mode S transponder and contains the discrete Mode S address of the sending aircraft. The pilot can select three modes of TCAS operation: standby, traffic advisory-only, and automatic. These modes are used by the TCAS logic to determine the sensitivity level. In a TCAS/TCAS encounter, each aircraft transmits Mode S coordination interrogations to the other to ensure the selection of complementary resolution advisories.
