What is the MRA if none is published for an airway?

When no Minimum Reception Altitude (MRA) is published for an airway, the MRA defaults to being equal to the Minimum Enroute Altitude (MEA). The MEA is primarily concerned with ensuring adequate obstacle clearance and providing reliable navigation signal reception.

In the absence of a specific MRA, utilizing the MEA as the MRA ensures that aircraft remain at or above the published altitudes that guarantee both obstacle avoidance and navigation signal reliability. Thus, it is safe for pilots to rely on the MEA when no other information regarding MRA is available. This means that even in areas without published MRAs, flying at or above the MEA provides the necessary safety margin for enroute flight.

This understanding reflects standards within aeronautical navigation procedures, emphasizing safety and the importance of adhering to established minimum altitudes in flight operations.