minimum safe altitude
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minimum safe altitude (MSA)
The altitude below which it is hazardous to fly because of the presence of high ground or other obstacles. MSAs are published for emergency use on instrument approach procedure (IAP) charts except RNAV (area navigation) IAPs. The MSA is defined using NDB (nondirectional beacon) or VOR (very high frequency omnidirection radio-range) facilities within a 25 (normally) or 30 NM (maximum) radius. If there is no VOR or NDB within 30 NM of the airport, there will be no MSA. The altitude shown provides at least 1000 ft of clearance above the highest obstacle in the defined sector.