If N12B is at 6,000 feet and cleared for approach, when can another aircraft receive clearance for 6,000 feet?

The correct choice is that another aircraft can receive clearance for 6,000 feet when N12B reports 5,000 feet. The reasoning behind this relies on maintaining safe vertical separation between aircraft.

When N12B, the first aircraft, is cleared for approach at 6,000 feet, it is important to ensure that another aircraft does not receive clearance to operate at the same altitude until it is clear that N12B is descending. Typically, air traffic control will wait until the first aircraft descends to a significantly lower altitude to ensure they are safely separated and to avoid potential conflicts.

By the time N12B reports its altitude as 5,000 feet, it indicates that it is actively descending towards the runway and is no longer a conflict with an aircraft that may be cleared to 6,000 feet. This ensures safety and compliance with standard separation protocols.

In contrast, receiving clearance at altitudes like 4,000 feet, on final approach, or while holding at 6,000 feet would not allow for the necessary vertical separation from the aircraft that is already in the approach phase, which could potentially lead to a dangerous situation. The answer emphasizes the need for a clear and established altitude separation to ensure safe operations in controlled