What happens once a pilot vacates an altitude under PD?

When a pilot vacates an altitude under Positive Control (PD), the expectation is that they will not return to that altitude. This is primarily due to the traffic management and safety protocols in place for airspace. Once a pilot descends or climbs away from an assigned altitude, that altitude is considered vacated, which allows air traffic control to manage the airspace more efficiently by assigning that altitude to other aircraft if necessary.

In this context, the rules of engagement dictate that the pilot must maintain their new altitude until further instruction is given by air traffic control or until they reach their destination. This ensures that the altitudes are safely separated from other aircraft, reducing the risk of collisions and maintaining the flow of air traffic.

The other choices either imply a return to the previous altitude, which undermines the separation protocols, or suggest an automatic climbing path or permanent clearance that may not be relevant to the scenario of vacating an altitude under positive control.