What should be done before conducting transponder testing?

Before conducting transponder testing, it is essential to notify Air Traffic Control (ATC) because transponder testing can affect the aircraft's ability to communicate its position and intentions to ATC. Transponders play a key role in ensuring safe air traffic management by providing identification and altitude information about aircraft to air traffic controllers.

By notifying ATC, the aircraft ensures that controllers are aware the transponder will not be used in a conventional manner during the testing period. This prevents any confusion or miscommunication that may arise if controllers observe an aircraft that appears to be unresponsive or is not reporting its location correctly while performing tests. This collaboration is crucial for maintaining safety in the airspace, as other aircraft operations will be adjusted to accommodate the testing.

The other options do not align with standard procedures. While notifying local airports or ground crew can be part of general operation protocols, the primary requirement in this context focuses on maintaining safe and clear communication with ATC during the transponder testing process.