What is the definition of the Minimum Enroute Altitude (MEA)?

The definition of Minimum Enroute Altitude (MEA) is focused on two key aspects: obstacle clearance and navigational signal coverage. It is the lowest published altitude that ensures aircraft can safely navigate through a given segment of airspace without the risk of collisions with terrain or obstacles, while also ensuring that the navigation aids providing guidance and position information are reliable and effective.

By meeting the required obstacle clearance, MEA ensures that aircraft maintain a safe vertical distance from the ground. Additionally, the altitude must maintain acceptable coverage of navigational signals, which is critical for the pilot's situational awareness and navigation accuracy.

The other options introduce additional conditions that exceed the basic definition of MEA. While two-way radio communications, adequate radar coverage, and DME mileage are important in various contexts of aviation operations, they are not encapsulated within the essential definition of MEA. Thus, the chosen definition correctly reflects the primary purpose of MEA in maintaining safety during enroute flight.