What should be done with the last assigned altitude after receiving an approach clearance while being radar vectored?

The best course of action after receiving an approach clearance while being radar vectored is to maintain the last assigned altitude until established on a published route segment. This directive is crucial because it ensures safe and orderly integration into the approach procedure without inadvertently descending below safe altitudes or entering areas of controlled airspace without appropriate clearance.

By keeping the last assigned altitude, pilots can manage their descent in a way that aligns with both the radar controller's instructions and the standard operating procedures for the approach. This approach allows the controller to maintain separation from other aircraft and provides the pilot with the necessary context to safely transition onto the published approach path. Once the aircraft is established on the specified segment of the approach, they can then descend as instructed or as necessary in conjunction with further air traffic control guidance.

In contrast, acting on other options could lead to safety concerns; for example, descending immediately could result in conflicts with other aircraft, while climbing to the assigned altitude would contradict the intention of the approach clearance and delay the approach process.