GlossaryAirspace
AirspaceClass A Airspace
Also: Class A
The high-altitude controlled airspace running from 18,000 feet MSL up through FL600, where every flight must be operated under instrument flight rules.
“Class A airspace is generally the airspace from 18,000 feet mean sea level (MSL) up to and including flight level (FL) 600, including the airspace overlying the waters within 12 nautical miles (NM) of the coast of the 48 contiguous states and Alaska.”
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