Definition
An altitude depicted on an approach chart that provides at least 1,000 feet of obstacle clearance within a defined radius (typically 25 nautical miles) of a specified navigation facility, waypoint, or airport reference point. The MSA is intended for emergency use only and may not guarantee acceptable navigation signal coverage.
Plain English
It is a safe-from-terrain altitude shown on an approach chart that you can use in an emergency. If you stay at or above it within the marked area around the chosen point, you will clear the ground and obstacles by at least 1,000 feet.
Context Anchor
Seen in FAA rules, the AIM, training discussions, and flight planning when deciding how low an aircraft may legally or safely operate.
Derivation
Minimum means the lowest allowed; safe altitude refers to a height that keeps the aircraft clear of terrain and obstacles. The phrase as a whole names the lowest altitude in a given area that is still safe with respect to what is below.
Why Pilots Care
Gives a reliable safety buffer when descending in instrument conditions or when communications are lost.
Grounding Statement
This altitude is a lower limit: if you go below it without a valid reason such as takeoff or landing, you may no longer have enough safety margin from what is below you.
Intuition Check
Do not read “minimum safe” as “the best altitude to fly” or as a guarantee that every situation is safe. It means the lowest altitude the rule or procedure identifies for that situation; a pilot may still need to fly higher.
Example Sentence 1
After losing situational awareness in the clouds, the pilot climbed to the minimum safe altitude specified on the approach chart before contacting ATC for help.
Example Sentence 2
Before starting the approach, verify the MSA to maintain terrain clearance if vectors are lost.