When flying the VOR approach in a category C aircraft, to which MDA may you descend if TACAN is inoperative?

In this scenario, the key factor when flying a VOR approach in a category C aircraft is the Minimum Descent Altitude (MDA) established for the approach, particularly when associated equipment such as TACAN is inoperative.

For a category C aircraft, the MDA value is determined by specific altitude guidelines provided in the approach procedure. Typically, if TACAN is not available, pilots would refer to the approach chart to ascertain the MDA that still meets the approach requirements, taking into account the highest minimums for the relevant approach.

The MDA allows pilots to safely descend to a specific altitude where they can continue making a visual reference to the runway, provided they have adequate visual references in sight by that altitude. Thus, the MDA of 680 feet MSL is the correct answer, reflecting the proper altitude for a category C aircraft when executing a VOR approach without TACAN.

It's essential to always confirm the specific approach and its requirements from the relevant charts to ensure compliance with safety standards and regulations.