What is the timeframe within which an ATC transponder must be tested and inspected?

The correct answer is based on the regulations governing the testing and inspection of ATC transponders. According to the Federal Aviation Administration (FAA) regulations, an ATC transponder must be tested and inspected every 24 calendar months. This periodic maintenance ensures that the transponder operates correctly and meets safety standards essential for air traffic control communications. Regular testing is vital for the reliability of the transponder’s function in identifying aircraft to air traffic controllers and ensuring safe separation between aircraft in controlled airspace.

The other timeframes, while they may seem plausible, do not align with the established FAA requirements. Specifically, 12 and 18 months are too short for the required inspection period, while 36 months exceeds the maximum allowable interval for transponder checks. Adherence to the 24-month schedule helps maintain consistent operational standards and enhances overall aviation safety.