What altitude constraint applies to the 45/180° method on approach?

The correct answer reflects the requirement that during the 45/180° maneuver, the descent should begin when the aircraft is outbound and abeam a specified VORTAC. This maneuver is typically employed in circling approaches or when executing a missed approach, where precise altitude management is critical for maintaining safe vertical separation from the terrain and for adhering to approach procedures.

Beginning the descent specifically when the aircraft is abeam the VORTAC provides a clear point in the procedure to ensure that the descent is executed safely and that the aircraft is positioned correctly for the subsequent legs of the approach. This timing allows pilots to have a defined point in their navigation where they can start their descent while ensuring adequate altitude is maintained during the outbound leg of the maneuver.

The other options may not align with the standard operating procedures for this approach method, as they either suggest a lack of constraints or inappropriate timing for descent, which could lead to safety issues in actual flight operations. Thus, adhering to the altitude constraint while implementing this technique is essential for maintaining safe flight practices.