What does MEA ensure during navigation?

The correct choice relates to the Minimum Enroute Altitude (MEA) in aviation navigation, which specifically ensures a safe clearance over obstacles and provides adequate navigation signal reception. MEA is established for segments of an air route to guarantee that aircraft maintain a minimum vertical clearance above terrain and obstacles. This is typically a clearance of at least 1,000 feet above the highest obstacle in a designated area when flying up to 2,000 feet, which minimizes the risk of collision with terrain or obstacles.

In addition to providing vertical obstacle clearance, MEA also ensures that pilots will have reliable navigation signal reception from ground-based navigation aids. This is crucial for maintaining situational awareness and effectively navigating along airways.

The other options, while important in the broader context of aviation and navigation, do not specifically encapsulate what MEA guarantees. For instance, visibility of 3 statute miles and ground speed requirements pertain to different regulations and conditions applicable to flight operations, while continuous vertical navigation refers to a concept in more advanced navigational systems rather than the specific purpose of MEA.