Under what condition can a controller request a code change from an aircraft outside their area of responsibility?

A controller can request a code change from an aircraft outside their area of responsibility when it has been coordinated at the time of handoff or specified in a Letter of Agreement (LOA). This is critical in ensuring that air traffic control operates smoothly and that responsibilities are respected between different sectors or facilities.

In situations where a handoff occurs, coordination ensures that the next controller has the pertinent information for managing the aircraft, including any code changes that may need to be implemented for effective tracking and communication. Similarly, messages or procedures specified in an LOA further outline expectations and responsibilities between the involved parties, facilitating seamless transitions and operations.

This process does not extend to situations like radar identification or when the aircraft is flying VFR, as those conditions do not necessarily relate to inter-facility coordination requirements. Moreover, special military operations might have their own set of unique protocols that do not automatically permit code changes without prior agreement. Thus, the most applicable condition is one where there is clear coordination in play, ensuring that all controllers involved are aligned on the required actions for the aircraft in question.