Definition
An emergency-use altitude published on instrument approach charts that provides at least 1,000 feet of obstacle clearance within a defined radius (typically 25 nautical miles) of a specified navigation fix, usually the airport reference point or a primary navaid. MSAs are depicted as one or more sectors around that fix, each labeled with the lowest altitude that guarantees the required obstacle clearance in that sector. They are intended for emergency use only and do not necessarily provide acceptable navigation signal coverage.
Plain English
A set of altitudes printed on the approach chart that tell you the lowest height you can safely fly in each direction around the airport without hitting terrain or obstacles. They're there as a safety net if something goes wrong during an approach.
Context Anchor
Seen on instrument approach charts, usually in the plan view area, where it gives emergency altitude guidance around the procedure.
Derivation
Minimum comes from a Latin word meaning “smallest,” and altitude means height. In this aviation use, the phrase points to the lowest published height that still gives required obstacle clearance for a defined area.
Why Pilots Care
Gives pilots a known safe altitude to descend to without hitting terrain when normal navigation or ATC guidance is lost.
Grounding Statement
Think of MSA as an emergency obstacle-clearance floor for the area around an instrument procedure.
Intuition Check
“Safe” does not mean risk-free or suitable for normal cruising. Here it means the altitude gives required obstacle clearance in the defined area, mainly for emergency use.
Example Sentence 1
After losing situational awareness on the approach, the pilot climbed to the published MSA of 4,200 feet for that sector and contacted ATC for vectors.
Example Sentence 2
The MSA around the airport VOR kept the aircraft 1,000 feet above all obstacles within 25 miles.