Upon crossing the SIDON VORTAC at 10,000 feet and cleared for the approach, when is a pilot allowed to descend?

The correct answer is that a pilot is permitted to descend outbound abeam the VORTAC. This is in accordance with standard procedures for approach transitions, where the pilot typically holds altitude until they are established on the prescribed track, which often occurs when they pass a navigation aid like the VORTAC.

Descending outbound abeam the VORTAC aligns with the procedures for managing altitude in relation to the approach, ensuring that the aircraft is safely positioned for the next stages of the approach. This allows the pilot to maintain a safe margin while properly configuring the aircraft for descent as the approach progresses.

The other options do not accurately capture the operational procedures surrounding altitude changes upon passing the VORTAC. For example, simply descending immediately upon passing the VORTAC may not take into account the specific guidance and safety considerations in a controlled airspace environment. Permissions and instructions from ATC, as mentioned in the other choices, might also involve additional conditions or clearances before a descent can be initiated safely.