What should a pilot do when cleared for approach while being radar vectored on an unpublished route?

When a pilot is cleared for approach and is being radar vectored on an unpublished route, the correct action is to remain at the last assigned altitude until they are on a published route. This is crucial for several reasons.

Firstly, altitude management is important during the approach phase to ensure separation from other aircraft and to comply with air traffic control (ATC) instructions. When ATC provides a radar vector, they are often managing multiple aircraft, and it is critical to adhere to their instructions until they provide further clearance.

Secondly, the use of published routes helps maintain standardization and safety in navigation. By remaining at the last assigned altitude, the pilot is ensuring they don't descend inadvertently into airspace where radar vectors haven't established safe separation, particularly in scenarios where an unpublished route may present complexities in altitude considerations.

The other options present actions that could potentially lead to unsafe situations or miscommunication with ATC. For instance, immediate descent could result in uncontrolled altitude changes, which are problematic if not coordinated; changing to approach frequency prematurely may confuse ATC and lead to loss of situational awareness; and proceeding to the destination at the same altitude without guidance to change could lead to an out-of-sequence arrival or conflict with other aircraft. Thus, maintaining the