Definition
The lowest altitude, expressed in feet above mean sea level (MSL), to which a pilot may descend during a circling approach maneuver in a non-precision instrument approach procedure. The aircraft must remain at or above this altitude until the pilot has the required visual reference to the runway environment and is in a position to make a normal descent to landing.
Plain English
When you fly an instrument approach but need to circle around to land on a different runway, this is the lowest you're allowed to go until you can see the airport and line up for a normal landing.
Context Anchor
Seen on instrument approach charts and in cold-temperature correction discussions, where a pilot may need to adjust published minimum altitudes for very cold conditions.
Derivation
"Circling" refers to the visual maneuver of flying around the airport at low altitude to align with a runway. "Minimum Descent Altitude" comes straight from its function: the minimum altitude (lowest point) a pilot may descend (go down) to during this segment. The phrase is descriptive rather than borrowed from another language.
Why Pilots Care
Provides the minimum safe height for maneuvering around the airport to land while protecting against terrain or obstacles.
Analogy
Think of it as a safety floor. You may fly at or above that floor while circling, but you do not go below it until you are in a proper position to continue safely to the runway.
Intuition Check
“Circling” here does not mean flying random circles around the airport. It means a specific visual maneuver after an instrument approach to position the aircraft for landing on a runway. “Minimum” does not mean the best altitude to fly; it means the lowest altitude you are allowed to use in that part of the procedure.
Example Sentence 1
After breaking out of the clouds at the Circling MDA, the pilot maneuvered the aircraft to align with Runway 27 and began a normal descent to landing.
Example Sentence 2
Without the required visual references by the circling MDA, the crew initiated the published missed approach.