When is it permissible to assign an altitude to an aircraft?

Assigning an altitude to an aircraft is permissible only after the aircraft previously at that altitude has reported passing through another altitude with appropriate minima. This practice ensures that there is a safe separation between aircraft, which is crucial for maintaining air traffic safety.

In this case, the process of managing altitude assignments hinges on the need for confirmed separation and situational awareness. When a previously assigned aircraft has reported that it has vacated an altitude—while adhering to the required vertical separation minima—it indicates that the altitude is now available for assignment to another aircraft. This procedure minimizes the risk of vertical conflicts and enhances safety in busy airspace.

Understanding this is vital for controllers, as they must maintain thorough situational awareness and compliance with separation standards at all times. The other circumstances may involve considerations and regulations, but they do not guarantee the absence of conflicts or the safety required for altitude assignments as effectively.