24-month checks check which item?

• A. Altimeter
• B. Transponder
• C. Fuel Gauge
• D. Magnetos

Answer: (B)

Periodic equipment checks are used to keep critical avionics reliable, and the 24-month interval specifically applies to the transponder. The transponder is what your aircraft uses to respond to radar with a discrete code and, in many cases, altitude information. To ensure ATC can accurately identify you and receive your altitude data, regulations require the transponder to be tested and inspected at least once every 24 calendar months. A qualified technician performs the check and issues documentation confirming proper operation, including coding and mode operation.

Other items have their own maintenance or calibration paths that aren’t defined by this particular 24-month interval. The altimeter involves static system calibration and altitude encoding accuracy, which are addressed through separate checks; fuel gauges and magnetos have different inspection and maintenance schedules tied to other requirements (such as annual or engine-related checks) rather than this 24-month transponder rule.