Which AN/TPX-42A Secondary Surveillance Radar (SSR) interrogation mode is continuously operable?

The AN/TPX-42A Secondary Surveillance Radar (SSR) utilizes several interrogation modes, each serving specific purposes in air traffic management and aircraft identification. Mode C is designed to provide altitude information in addition to the aircraft's identity.

What makes Mode C particularly notable is its continuous operability feature, which allows it to function without interruption for sustained periods. This means that while interrogating targets, it can consistently receive altitude data, providing real-time information about aircraft's vertical positions in relatively busy airspace.

In contrast, other modes such as Mode 1, Mode 2, and Mode 3/A have specific operational limitations or scenarios they are primarily designed for, therefore lacking the same continuous functionality. Mode C’s capability to operate continuously is critical for effective air traffic monitoring and safety, especially in environments where altitude awareness is vital for avoiding collisions and maintaining safe separation between aircraft.