When can you assign an altitude occupied by another aircraft?

The correct answer indicates that you can assign an altitude occupied by another aircraft after issuing a clearance for that aircraft to climb or descend and confirming that it has left that altitude. This procedure is crucial for maintaining safe separation between aircraft.

Air traffic control is responsible for ensuring that sufficient distance exists between different aircraft to prevent collisions and ensure safe operations in the airspace. When an aircraft is given a clearance to change altitude, the controller must continue to monitor that aircraft's progress. Only once the controller has verified that the aircraft has left the altitude it was previously occupying can they safely assign that altitude to another aircraft.

Assigning an altitude before the previous occupant has reported leaving it, as suggested in the first option, creates the risk of conflict and can lead to dangerous situations. Controlled airspace does impose some separation standards, but it alone does not allow for altitude assignment in the absence of confirmation regarding aircraft movements. Lastly, granting immediate altitude changes upon request without verification could lead to dangerous situations, as altitude separation could be compromised.

Understanding this protocol is essential for maintaining safety and efficiency in busy airspace, and it is a fundamental aspect of an air traffic controller's responsibilities.