When flying a VOR approach in a Cat C jet with a single VOR/DME receiver, what MDA may you descend to if the TACAN is inoperative?

In a VOR approach, the Minimum Descent Altitude (MDA) is determined based on the aircraft category and the operational parameters. For a Category C aircraft, the MDA is established to ensure a safe margin above obstacles and to maintain a safe environment while conducting the approach.

When a TACAN is inoperative, the use of the VOR approach must still comply with the established approach minimums. For Category C aircraft, the MDA is generally set to ensure that the aircraft can safely navigate while adhering to the obstacle clearance requirements for the specific approach procedure.

In this particular case, if the TACAN is inoperative and the scenario requires descending on a VOR approach, the MDA that allows for compliance with safety protocols while navigating the approach is 680 MSL. This altitude has been established for Category C jets under these circumstances, balancing safety with operational capability.

Therefore, descending to 680 MSL is appropriate because it meets the approach requirements while allowing for safe navigation and obstacle clearance during the final approach phase.