minimum descent altitude

Also found in: Acronyms.

minimum descent altitude (MDA)

A specified altitude or height in a non-precision approach or circling approach below which descent must not be made without the required visual reference (ICAO). The MDA is referenced to the mean sea level, and the MDH is referenced to the aerodrome elevation or the threshold elevation if that is more than 7 ft (2 m) below the aerodrome elevation. An MDH for a circling approach is referenced to the aerodrome elevation. The required visual reference means that section of the visual aids or of the approach area that should have been in view for sufficient time for the pilot to assess the aircraft position in relation to the desired flight path. In the case of the circling approach, the required visual reference is the runway environment.
References in periodicals archive ?
This technique has the aircraft quickly descending to the minimum descent altitude (MDA), and then flying level at the MDA until reaching the missed approach point (MAP).
The NTSB again: "Radar data and an air traffic controller confirmed that the airplane was circling at or below the minimum descent altitude of 720 feet (708 feet above ground level [agl]) while flying in and out of an overcast ceiling that was varying between 600 feet and 1100 feet agl.
Another theme running through these accidents is descending below the circling minimum descent altitude (MDA).
To understand the VDA and additional vertical guidance provided by today's navigation equipment, it helps to go back 20-plus years to the advent of CANPA, which stands for "constant-angle non-precision approach." This concept, which received a lot of visibility in the 1990s, is the stabilized-approach alternative to the time-honored practice of crossing the FAF or an intermediate, step-down fix on a non-precision approach (NPA) and then increasing the aircraft's rate of descent to arrive at the minimum descent altitude (MDA) well in advance of reaching the airport.
Another way to keep it all straight is to look for the decision altitude (DA) designation versus the minimum descent altitude (MDA) abbreviation on the approach plate's minima line.
She noticed the airplane was "high and fast" on final approach, so she used speed brakes and flaps to slow the airplane and descend to the minimum descent altitude. As the airplane descended below the ceiling, she observed runway lights and attempted to land on the runway.
Procedures using GPS to generate an electronic glidepath through baro-VNAV may not provide obstacle clearance below the procedure's minimum descent altitude (MDA).
The NTSB's probable cause finding included "the flight crew's operation of the airplane below the minimum descent altitude without an appropriate visual reference for the runway" and the FAA's "unclear wording" of a Notam on nighttime restrictions for the VOR/DME-C procedure the crew was executing, along with "the FAA's failure to communicate" the Notam's restriction to the tower.
The Cessna crew, however, made a mistake common when flying non-precision approaches with a minimum descent altitude (MDA) level-off.
whether it's the decision height, decision altitude or minimum descent altitude. Because the altitude for a given approach on a given day will vary depending on the equipment you're using, your airplane's approach category for the speed you're flying, and whether you will be flying a circling approach, it's vital to pick the proper altitude from the many options on the approach chart during your briefing prior to TOD, so you can commit it to short-term memory and confirm it just before reaching the FAF.

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