What is used to determine the minimum reception altitude when MRA is not published for an airway?

The minimum reception altitude (MRA) is the lowest altitude at which reliable VHF navigation signals can be received, particularly when navigating via airways. In cases where the MRA is not published, the minimum enroute altitude (MEA) serves as a key indicator for determining this minimum reception altitude. The MEA is designed not only to provide adequate obstacle clearance but also to ensure reliable navigation signal coverage along the airway.

When no specific MRA is available, referencing the MEA is appropriate because it guarantees that the aircraft will be at an altitude that is safe from terrain while also being above the minimum signal reception required for effective navigation. It is important to note that, while the MRA is effectively the same as the MEA, it's utilized in this context to ensure proper route adherence and signal reliability.

The lowest safe altitude and minimum vectoring altitude serve different purposes, focusing on safety margins and area navigation assistance, respectively. The aircraft's service ceiling is related to performance limits rather than navigation reception. By choosing the MEA in lieu of a published MRA, pilots can navigate safely and effectively within controlled airspace.