Lowest safe altitude

In aviation (particularly in air navigation) lowest safe altitude (LSALT) is an altitude that is at least 1,000 feet above any obstacle or terrain within a defined safety buffer region around a particular route that a pilot might fly. The safety buffer allows for errors in the air by including an additional area that a pilot might stray into by flying off track. By flying at or above this altitude a pilot complies with terrain clearance requirements on that particular flight leg.

Australian definition

• The minimum LSALT is 1500 feet.
• LSALT is 1360 feet above the highest obstacle which is less than 360 feet above the terrain.
• LSALT is 1000 feet above the highest obstacle which is greater than 360 feet above the terrain.

For example, if there is an obstacle at 200 feet above terrain of 2500 feet, LSALT is 2700 feet (obstacle height) + 1360 feet (clearance height), or an LSALT of 4060 feet; if there is an obstacle at 450 feet above terrain of 3600 feet, LSALT is 4050 feet (obstacle height) + 1000 feet (clearance height), or an LSALT of 5050 feet.

The differences in the clearance heights for obstacles is due to the potential for unreported obstacles up to 360 feet which are not marked on maps or charts.

The determination of which is the highest obstacle along the flight path depends on the method of navigation (radio navigation aid, dead reckoning or area navigation systems) and on the flight rules (instrument or night VFR)

FAA definition

In the United States in particular, the Federal Aviation Administration calls this concept the Minimum Safe Altitude (MSA), and specifically defines it as follows in § 119 of Part 91 of the Federal Aviation Regulations (FAR):

1. Anywhere: an altitude allowing a safe emergency landing without undue hazard to person or property on the ground;
2. Over Congested Areas: an altitude of 1,000 feet above the highest obstacle within a horizontal distance of less than 2,000 feet;
3. Over Populated Areas: an altitude of 500 feet AGL;
4. Over Open Water or Sparsely Populated Areas: an altitude allowing for a linear distance greater than 500 from any person, vessel, vehicle, or structure;
5. Helicopters: an altitude lower than in definitions 2, 3, and 4 above, as long as it is not in violation of definition 1 and in compliance with any routes or altitudes specifically prescribed for helicopters by the Administrator.

External links

• Civil Aviation Safety Authority - Australia
• eCFR Title 14 §91.119 Minimum safe altitudes: General