Definition
Minimum Safe Altitude (MSA) is an emergency altitude depicted on instrument approach charts that provides at least 1,000 feet of obstacle clearance within a specified radius (typically 25 nautical miles) of a designated reference point, usually the airport or a navigation facility associated with the approach. It is intended for emergency use only and does not necessarily guarantee navigation signal reception or compliance with ATC instructions.
Plain English
A backup altitude shown on approach charts that keeps you safely above terrain and obstacles within a set distance of the airport, meant for use if something goes wrong during an approach.
Context Anchor
Seen on instrument approach charts, especially near the plan view of the approach, where it gives a quick emergency altitude reference for the area around the approach.
Derivation
From Latin minimum (smallest) and the everyday word safe. The 'safe' here is specifically about clearing terrain and obstacles — not about overall flight safety in every sense.
Why Pilots Care
Prevents controlled flight into terrain when flying in clouds or at night over unfamiliar or mountainous areas.
Intuition Check
“Minimum safe” does not mean the lowest altitude that is safe for normal flying in every situation. Here it means a charted emergency altitude that gives obstacle clearance within a defined area.
Example Sentence 1
After losing communications during the approach, the pilot climbed to the published MSA of 4,300 feet to ensure terrain clearance while troubleshooting.
Example Sentence 2
Because the terrain rose sharply to the north, the MSA on that approach was 1,800 feet higher than on the opposite runway.