Definition
Class A is a category of regulated airspace in the United States extending from 18,000 feet MSL up to and including Flight Level 600 (60,000 feet), over the 48 contiguous states, Alaska, and the airspace overlying the waters within 12 nautical miles of the coast. All operations within Class A airspace must be conducted under Instrument Flight Rules (IFR), and aircraft must be on an IFR clearance from Air Traffic Control. Pilots must hold an instrument rating, and aircraft must be appropriately equipped for IFR flight.
Plain English
Class A is the high-altitude airspace that begins at 18,000 feet and goes up to 60,000 feet. Every flight inside it must be on an IFR clearance with ATC -- there is no VFR flying allowed in this airspace.
Context Anchor
Seen in airspace diagrams, instrument training, and flight planning for high-altitude operations.
Derivation
The FAA labels its six airspace categories with letters A through G (skipping F, which is unused in the U.S.). 'A' sits at the top of the alphabet and the top of the airspace stack -- the highest, most strictly controlled category where IFR is mandatory.
Why Pilots Care
Entry requires an instrument rating and an active IFR flight plan to ensure traffic separation at high altitudes.
Intuition Check
Class A does not mean “best” or “most important.” It means a specific FAA airspace category with specific rules, altitude limits, and clearance requirements.
Example Sentence 1
Once we climb through 18,000 feet, we'll be in Class A airspace, so we need our IFR clearance before departure.
Example Sentence 2
Jets typically cruise inside Class A airspace at flight levels between 290 and 410.