When two aircraft are arriving at the same airport holding over the same IAF fix, what altitude requirement is necessary for separation?

Answer: D — No altitude separation needed

In scenario where two aircraft are holding at the same Initial Approach Fix (IAF), the requirement for vertical separation is governed by air traffic control procedures. Specifically, when aircraft are holding over the same fix, vertical separation is not necessary as long as they are in a holding pattern, maintaining their assigned altitudes. Each aircraft is typically sequenced and instructed to hold at a specific altitude and position, ensuring they remain safely separated in terms of horizontal distance as they fly their respective holding patterns. In such circumstances and under standard procedures, the need for altitude separation typically does not apply, as the established hold specifics provide the necessary safety and separation between the aircraft.