Which of the following is a requirement when cleared for the approach?

When cleared for the approach, the requirement is to commence descent as per the approach clearance. This means that once air traffic control has provided the necessary instructions for the approach, the pilot must begin to descend in accordance with the specified altitudes and any other instructions included in that clearance.

This is critical for maintaining the proper flight path and ensuring safe separation from other aircraft and terrain. The approach clearance typically includes specific altitudes and waypoints that the pilot is expected to adhere to, so commencing the descent in a timely manner is essential to ensuring compliance with those parameters and facilitates a smooth transition to landing.

The other options, while they may have relevance in different contexts, do not specifically address the actions mandated by an approach clearance. Attaining cruising altitude, for instance, is more relevant during the en route phase of flight rather than the approach phase. Turning off non-essential systems might be prudent for safety but is not a requirement directly tied to approach clearance. Flying at minimum altitude is also a consideration but is contingent on the specific approach procedures rather than a blanket requirement upon receiving the clearance.