Minimum Descent Altitude (MDA)
Minimum Descent Altitude (MDA) is the lowest altitude to which an aircraft may descend on a non-precision instrument approach without the required visual reference established. Unlike a Decision Height (DH) — where the aircraft is on a continuous descent — the MDA is a level-off altitude: the pilot levels the aircraft at MDA and flies level to the Missed Approach Point (MAP) looking for visual reference.
MDA vs. DH
- MDA (Minimum Descent Altitude): Used for non-precision approaches (VOR, NDB, LNAV); aircraft levels off at MDA and searches for visual reference to the MAP; no vertical guidance
- DH (Decision Height): Used for precision approaches (ILS, LPV); aircraft descends continuously on a glidepath; at DH, land or go missed immediately
Continuing Past MDA
Once at MDA, the aircraft may continue descending only when: 1) the required visual reference is established, 2) the aircraft is continuously in a position to land using a normal manoeuvre, and 3) conditions are at or above published minimums. Descent below MDA without visual reference is a serious violation and safety risk.
On the TC Written Exam
MDA vs. DH is a guaranteed exam distinction. Non-precision → MDA → level off → search for visual. Precision → DH → continuous descent → immediate decision.
Related Terms
See also: Decision Height, Missed Approach, Required Visual Reference.