Definition
The lowest altitude, expressed in feet above mean sea level (MSL), to which descent is authorized during a circling approach maneuver at the conclusion of an instrument approach procedure. The pilot must remain at or above this altitude until in a position to make a normal descent to the runway using normal maneuvers.
Plain English
When you fly an instrument approach and then circle around to land on a different runway, this is the lowest altitude you are allowed to fly during that circle. You stay at or above it until you are lined up close enough to descend normally to the runway.
Context Anchor
Seen on instrument approach charts and in discussions of cold-weather altimeter errors, where a pilot may need to correct published minimum altitudes for very cold temperatures.
Derivation
‘Circling’ describes the visual maneuver of flying around the airport to align with a different runway than the one the approach was designed for. ‘MDA’ is Minimum Descent Altitude — the floor for descent on a non-precision approach. Together: the descent floor while circling.
Why Pilots Care
Maintains safe clearance from terrain and obstacles during the visual segment of a circling approach, especially important in low ceilings or cold weather where true altitude is lower than indicated.
Intuition Check
Circling MDA does not mean you are free to circle at any low altitude that looks safe. It means you must not go below the published circling minimum altitude until you are properly positioned to make a normal landing.
Example Sentence 1
After breaking out of the clouds at the circling MDA, the pilot maneuvered to align with runway 27 before beginning the final descent.
Example Sentence 2
Cold weather required adding 300 feet to the published circling MDA to compensate for altimeter error.