Class A airspace generally begins from 18,000 feet mean sea level up to and including 60,000 feet. Operations in Class A are generally conducted under Instrument Flight Rules and primarily used by higher performance aircraft, airline and cargo operators, etc.

In the United States, the altitude range between 18,000 feet and 60,000 feet Mean Sea Level (MSL) is designated as Class A Airspace. This is a highly regulated environment where the "positive control" of all aircraft is mandatory. Every pilot operating in Class A airspace must be on an Instrument Flight Rules (IFR) flight plan and maintain constant radio communication with Air Traffic Control. This airspace covers the entire 48 contiguous states and Alaska, as well as the waters within 12 nautical miles of the coast. All major commercial airliners and high-performance business jets operate in this zone because it is where the "jet routes" are located, allowing for fuel-efficient, high-speed travel above the weather and general aviation traffic found at lower altitudes. To enter Class A, an aircraft must also be equipped with a transponder that provides altitude and identity information to controllers. Above 60,000 feet, the airspace technically transitions back to Class E, but because few civilian aircraft can maintain such high altitudes, Class A represents the "highway system" of the sky for modern commercial aviation.