How many TCAS antennas are typically installed on an aircraft?

The correct answer is that typically, two TCAS (Traffic Alert and Collision Avoidance System) antennas are installed on an aircraft. This setup is designed to ensure effective coverage and reliability in detecting nearby aircraft, as TCAS relies on transponder signals from other aircraft.

Having two antennas, usually one mounted at the top of the fuselage and one at the bottom, allows the system to accurately receive and transmit signals in three-dimensional space. This dual-antenna configuration helps to minimize the risk of signal obstruction and enhances the overall operational effectiveness of the TCAS in providing traffic advisories and resolving potential mid-air collision threats.

In contrast, aircraft that might have one, three, or four antennas would not adhere to the standard configuration for TCAS, which emphasizes the use of two antennas for optimal performance. This standardization ensures that the TCAS can function properly under various flight conditions and maintain safety in crowded airspace.