Answered By AOPA
What is the definition of Class "A" airspace?
AOPA Staff Answer
Airspace from 18,000 ft Mean Sea Level (MSL) up to and including Flight Level (FL) 600, including that airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous states and Alaska, and designated international airspace beyond 12 nautical miles of the coast of the 48 contiguous states and Alaska within areas of domestic radio navigational signal or ATC radar coverage, and within which domestic procedures are applied.
Most GA pilots do not fly in class A airspace due to its altitude structure. If you do, however, operate in class A, review FAR 91.135 for the requirements. All operations must be conducted under IFR, with an ATC clearance, and in communication with ATC. Some deviations are provided for.