Minimum Safe Altitude

MSA (Minimum Safe Altitude) is published on instrument approach charts showing the lowest altitude within 25 nautical miles of the navigation facility that provides at least 1,000 ft of obstacle clearance. MSA is divided into sectors (typically quadrants) with different altitudes based on terrain in each sector.

MSA is intended as an emergency reference — it guarantees obstacle clearance but does not guarantee navigation signal coverage or ATC radar coverage.