Controlled Airspace

Controlled airspace is a generic term that covers the different classification of airspace (Class A through Class E airspace) and in which air traffic control service is provided to IFR flights and to VFR flights.

Inside controlled airspace, controllers will provide safety alerts for:

• Terrain and obstructions, when an aircraft's altitude puts it in an unsafe proximity to terrain or obstructions
• Aircraft conflicts, when the controller controller observes another aircraft in an unsafe proximity

Class A Airspace

Purpose	Primarily for high-speed aircraft cruising.
Dimensions	18,000 feet MSL up to and including FL 600
Entry Requirements	All aircraft must operate under IFR, and be in contact with ATC 91.135 Required Mode C transponder and ADS-B out source

Class B Airspace

Purpose	Surrounds the nation's busiest airports in terms of IFR operations or passenger enplanements.
Dimensions	Individually tailed for each airspace, but generally extends up to 10,000' MSL. Designed to contain instrument approaches into the primary airport.
ATC Services	Sequencing and separation from other aircraft
Entry Requirements	Two-way radio communication 91.131 Pilot must hold at least a private pilots license, or a student/sport/recreation license with an endorsement 91.131 Obtains a specific clearance to enter, something akin to "Cleared into the class bravo" 91.131 For IFR operations a VOR receiver, or suitable RNAV system 91.131(c) Required Mode C transponder and ADS-B out source

Class C Airspace

Purpose	Surrounds busy airports with a control tower, TRACON, and a large amount of IFR traffic.
Dimensions	Usually a 5nm and a 10nm ring, extending up to 4,000' AGL.
ATC Services	Sequencing to primary airport, aircraft separation (including wake turbulence separation). Separation services outside the Class C provided on a workload-permitting basis.
Entry Requirements	Two-way radio communication with the ATC facility established 91.131 This should include reference to the aircraft's callsign, e.g. "N12382, standby", is sufficient Required Mode C transponder and ADS-B out source Cannot operate airspace at speeds above 200 KIAS.

Class D Airspace

Purpose	Surrounds airports with an operational control tower.
Dimensions	Tailed for each airport, but usually 4nm radius around the airport, up to 2,500' AGL.
ATC Services	No separation services are provided to VFR aircraft.
Entry Requirements	Two-way radio communication with the ATC facility established 91.131 This should include reference to the aircraft's callsign, e.g. "N12382, standby", is sufficient Cannot operate airspace at speeds above 200 KIAS.

Class E Airspace

Purpose	Supports terminal and enroute IFR traffic.
Dimensions	Begins at 14,500' MSL (up to 18,000' MSL), unless charted otherwise Most of the U.S. has Class E airspace charted as beginning at 1,200' AGL Also surface airspace around Class D airports with a closed control tower. Within 4nm of the centerline of a federal airway, from 1,200 AGL up to (but not including) 18,000' MSL.
ATC Services	No separation services are provided to VFR aircraft.
Entry Requirements	Two-way radio communication with the ATC facility established 91.131 This should include reference to the aircraft's callsign, e.g. "N12382, standby", is sufficient

Controlled Airpsace Weather Minimums

VFR Weather Minimums

References

• AIM Chapter 3, Section 2