What does a Minimum Descent Altitude (MDA) signify?

A Minimum Descent Altitude (MDA) is a critical safety parameter during non-precision instrument approaches. It signifies the lowest altitude to which an aircraft can descend without having the required visual reference to continue the approach. Essentially, the MDA establishes a point below which the aircraft must not descend unless visual references are acquired, allowing the pilot to safely transition from instrument flight to visual separation.

This altitude is particularly important to ensure that the aircraft remains clear of obstacles and maintains a safe margin above the terrain during the approach phases of flight. If the pilot does not see the required references at this altitude, they are mandated to execute a go-around, ensuring safety is prioritized.

The other choices do not accurately describe the function of MDA. For example, while the lowest altitude for maintaining controlled flight is relevant, it does not specifically address the operational context of MDA, which is tied to visual references during an approach. Similarly, the initiation of a go-around is not defined by MDA in a way that would suggest it is solely the altitude triggering that action, and maximum altitudes over populated areas pertain to different regulatory contexts not related to approach safety.