In the event of a communications failure in controlled airspace, which transponder code should a pilot select?

In the event of a communications failure while operating in controlled airspace, the proper transponder code to select is 7600. This code distinctly indicates to air traffic control that there is a communication failure, allowing them to recognize the situation and provide assistance to the pilot.

Using 7600 helps maintain safety by alerting ATC to the fact that the aircraft is unable to maintain two-way radio communication. This way, air traffic controllers can monitor the aircraft's situation and may take necessary actions, such as providing visual separation from other traffic or advising surrounding aircraft about the situation.

The other codes serve different purposes. For example, 7500 indicates a hijacking, which communicates a serious security threat rather than a communication issue. Code 7700 signifies an emergency, but it is a more general alarm for any emergency situation and does not specifically indicate a communications problem. The code 7501 does not exist; thus, it would not be appropriate to use in any situation. Understanding these specific transponder codes is crucial for pilots to communicate effectively with air traffic control during various scenarios.