Using the 45/180° method, when can an aircraft descend from 4,000 feet MSL?

Using the 45/180° method is a technique often employed in instrument flight rules (IFR) approaches, particularly in executing a procedure turn or a holding pattern. When an aircraft is at 4,000 feet MSL and is preparing to descend, the 45° turn typically refers to the turn away from the course to intercept the outbound leg of a procedure turn, and the 180° turn is executed to return towards the final approach.

In this context, option B indicates that the aircraft can descend while it is outbound and abeam a specific VORTAC, in this case, the Elm Grove VORTAC, while on a parallel heading. This condition allows for proper spacing, altitude management, and navigation as the aircraft transitions from the initial outbound segment back to the approach. The timing of the descent is crucial to ensure that the plane is correctly positioned and at an appropriate altitude to intercept the final approach course safely.

This method allows pilots to manage their altitude and ensure they are on the correct path as they prepare to begin the approach. In this scenario, descending at the outbound abeam point aligns with the procedural requirements of maintaining safe vertical and horizontal separation during the approach.