Minimum Sector Altitude

Minimum sector altitude (MSA) is the lowest altitude which will provide a minimum clearance of 300 m (1,000 ft) above all objects located in an area contained within a sector of a circle of 46 km (25 NM) radius centred on a significant point. It is published on instrument approach charts for emergency use.

MSA Usage

The MSA is not a normal approach altitude — it is for emergency use only, such as when the aircraft has lost navigation guidance or must manoeuvre away from the approach track. The MSA guarantees 1,000 ft obstacle clearance within 25 NM of the centre fix; normal approaches use lower published minimums based on more precise position knowledge.

Related Terms

See also: Minimum Safe Altitude, Final Approach.