What is the primary difference between MEA and MOCA in flight navigation?

The primary difference between Minimum Obstacle Clearance Altitude (MOCA) and Minimum Enroute Altitude (MEA) lies in their specific functions related to safety and navigation during flight. MOCA provides both obstacle clearance for terrain and navigational signal coverage within 22 nautical miles of a VOR (VHF Omnidirectional Range) station. This means that if a pilot flies at or above MOCA, they can be assured of a certain altitude that clears obstacles in the vicinity, as well as adequate radio reception from navigation aids.

On the other hand, MEA is primarily focused on ensuring that there is reliable navigational signal coverage, while also providing a certain level of terrain clearance. However, the MEA does not provide obstacle clearance in the same way that MOCA does, particularly in the areas that may be beyond the range of the navigation aid.

Thus, answer B is correct because it fully encompasses the dual purpose of MOCA, emphasizing both obstacle clearance and assurance of navigational signal coverage. This makes MOCA a critical altitude for ensuring safe navigation directly around obstacles as well as when reliant on navigation aids.