Class A airspace is regulatory in nature and generally consists of the airspace from 18,000ft MSL to FL600. Class A airspace is not depicted on any sectional or en route chart due to the large area and dimension, essentially the entire United States, that class A airspace encompasses.
Within the Contiguous United States, Class A airspace makes up the airspace over the United States, including the airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous states, from 18,000ft MSL up to and including FL 600 excluding the states of Alaska and Hawaii.
Over Alaska, Class A airspace includes the airspace over the state, including the airspace overlying the waters within 12 nautical miles of the coast, from 18,000ft MSL to FL600, but not including the airspace less than 1,500ft above the surface of the earth, and the airspace over the Alaska Peninsula west of longitude 160°00’00''W.
Additional offshore airspace areas are also classified as Class A airspace. Offshore Class A airspace dimensions are different from the Class A airspace over the United States. These offshore airspaces include (to name a few) the airspace above Hawaii, the Gulf of Mexico, and certain airspace above Canada and Atlantic and Pacific coasts. These airspaces are defined by lateral and longitude coordinates and bearings and radials from navigational aids. These airspaces are defined in FAA order JO 7400.11E.
Part 91.135 describes operational requirements to operate in Class A airspace.
To operate in Class A airspace, a pilot must:
Pilots may deviate from these operational requirements with ATC authorization by the ATC facility with jurisdiction of the airspace in question.
If a transponder becomes inoperative in flight, ATC may immediately approve operation within Class A airspace allowing the flight to continue to its destination, as well as any intermediate stops, or proceed to a place where repairs can be made, or both.
Other requests for deviation must be submitted in writing at least four days before the flight. ATC can authorize deviations on a continuing basis or for an individual flight
Part 91.215 requires all aircraft that operate in Class A airspace, with an exception for Unmanned Aircraft, to be equipped with an operable coded radar beacon transponder having either:
Aircraft must also be equipped with automatic pressure altitude reporting equipment with Mode C capability that automatically replies to Mode C interrogations by transmitting pressure altitude information in 100-foot increments.
Part 91.225 requires all aircraft that operate in Class A airspace after January 1, 2020, to be equipped with ADS-B and TIS-B unless authorized by ATC.
ADS-B equipment must meet performance requirements listed in TSO-C166b, Extended Squitter Automatic Dependent Surveillance-Broadcast.
TIS-B Equipment must operate on a radio frequency of 1090 Megahertz (MHz).
Both ADS-B and TIS-B equipment must also meet the requirements of Part 91.227, Automatic Dependent Surveillance-Broadcast (ADS-B) Out equipment performance requirements.
Class A Airspace also requires aircraft to be equipped with a two-way radio and maintain two-way radio communications with ATC while operating in Class A airspace, unless otherwise authorized by ATC, per Part 91.135
If VOR navigation equipment is required while operating above FL 240, the aircraft must be equipped with an approved DME or suitable RNAV system.
Required flight visibility and cloud clearances are not applicable to Class A airspace per Part 91.155.
This is primarily due to aircraft being required to operate under Instrument Flight Rules at all times while in Class A Airspace. However, this does not remove the pilot's responsibility to see and avoid per Part 91.113.
A pilot must hold at least a private pilot certificate with an instrument rating to meet the requirements to operate in Class A airspace.
Pilots may also require specific endorsements depending on the type of aircraft to be flown, commonly found in Class A airspace. These could include complex, high-performance, and high-altitude endorsements per Part 61.31
The only speed restriction, other than one given by ATC, in Class A airspace is that an aircraft is not allowed to travel faster than the speed of sound (greater than Mach 1) while operating in the United States without special flight authorization.
Other airspaces list their speed restrictions in Part 91.117. However, Class A airspace does not apply to any of these restrictions.