What is the maximum allowable time period for using an ATC transponder after it has been tested?

The maximum allowable time period for using an ATC transponder after it has been tested is 24 calendar months. This requirement is established by the Federal Aviation Administration (FAA) and is important for ensuring that the transponder operates correctly and reliably. Regular testing and maintenance are crucial for safety and compliance in aviation operations.

Using an ATC transponder that has not been tested within this timeframe could lead to safety issues and violations of FAA regulations. Therefore, maintaining awareness of this time limit is essential for pilots and operators to ensure that they remain in compliance and that their equipment functions effectively during flight operations. After the 24-month period, a transponder must be re-tested to continue its use legally in controlled airspace.