Minimum Descent Altitude (MDA)
Definition
The Minimum Descent Altitude (MDA) is the lowest altitude, expressed in feet above mean sea level (MSL), to which an aircraft may descend on a non-precision instrument approach without having the required visual references for landing in sight. The MDA is designed to provide a safe vertical buffer above obstacles until a missed approach is initiated or a landing is made.
Purpose
- Ensure obstacle clearance during the final segment of a non-precision approach
- Define the limit of descent without visual contact with the runway
- Support decision-making between continuing visually or executing a missed approach
Where MDA Applies
- Non-precision approaches (e.g., VOR, NDB, RNAV (LNAV), LOC)
- Circling approaches, where maneuvering to a runway other than that aligned with the approach is required
- Visual segments after some RNAV or step-down approaches
Key Characteristics
| Attribute | Description |
|---|---|
| Published on approach charts | Specified for each aircraft category (A–D) |
| Not a decision altitude | Descent must stop at or before reaching MDA |
| Time or distance-based missed approach | Must initiate go-around at MAPt if visual contact not established |
| Obstacle clearance built-in | Usually ~295 ft above highest obstacle within protected area |
MDA vs. Decision Altitude (DA)
| Feature | MDA | DA (Precision Approach) |
|---|---|---|
| Used on | Non-precision approaches | Precision approaches (e.g., ILS) |
| Descent profile | Step-down to altitude, then level | Continuous descent to DA |
| Action at minimum | Must not descend below until visual | Must initiate missed approach immediately if no visual |
| Go-around point | After reaching MAPt (Missed Approach Point) | At DA |
Example Phraseology
- “Minimum descent altitude 1,200 feet.”
- “Holding MDA until missed approach point.”
- “No contact at MDA, going around.”
Visual Reference Required to Continue Below MDA
You may descend below MDA only when:
- ✅ The runway environment is clearly in sight (e.g., runway lights, markings, threshold)
- ✅ You can make a normal descent and landing
- ✅ Visibility is equal to or better than the required minimums
Pilot Tips
- ✅ Begin level-off early to avoid busting MDA
- ✅ Use altitude callouts and checklists during final approach
- ✅ Practice MDA scenarios in LearnATC's non-precision modules
- ✅ Always know your aircraft category and refer to the correct minima column on the approach chart
Related Terms
- Missed Approach Point (MAPt) – the point at which you must decide to land or go around
- OCH (Obstacle Clearance Height) – used in calculating MDA
- Circling MDA – higher minima used when circling to a different runway