What does MDA indicate in relation to the highest runway elevation in the touchdown zone?

MDA, or Minimum Descent Altitude, represents the lowest altitude to which an aircraft can descend on an approach without visual reference to the runway. When specifically related to the touchdown zone, MDA signifies the height above touchdown at which a pilot must decide whether to continue the approach or execute a missed approach. It acts as a safety threshold, allowing pilots to confirm their position and proximity to the runway, thus ensuring adequate altitude above any terrain or obstacles that might be present during the final stages of approach.

Understanding MDA is critical for maintaining safe vertical separation from the runway and any surrounding terrain, thereby playing an essential role in the approach phase of flight.