Controlled Airspace

Controlled airspace is a generic term that covers the
different classifications of airspace and defined dimensions
within which air traffic control (ATC) service is provided
in accordance with the airspace classification. Controlled
airspace consists of:
• Class A
• Class B
• Class C
• Class D
• Class E

Class A Airspace
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. Unless otherwise authorized, all operation in
Class A airspace is conducted under instrument flight rules
(IFR).

Class B Airspace
Class B airspace is generally airspace from the surface to
10,000 feet MSL surrounding the nation's busiest airports in
terms of airport operations or passenger emplacements. The
configuration of each Class B airspace area is individually
tailored, consists of a surface area and two or more layers
(some Class B airspace areas resemble upside-down wedding
cakes), and is designed to contain all published instrument
procedures once an aircraft enters the airspace. An ATC
clearance is required for all aircraft to operate in the area,
and all aircraft that are so cleared receive separation services
within the airspace.

Class C Airspace
Class C airspace is generally airspace from the surface
to 4,000 feet above the airport elevation (charted in
MSL) surrounding those airports that have an operational
control tower, are serviced by a radar approach control,
and have a certain number of IFR operations or passenger
enplanements. Although the configuration of each Class C

area is individually tailored, the airspace usually consists of
a surface area with a five NM radius, an outer circle with
a ten NM radius that extends from 1,200 feet to 4,000 feet
above the airport elevation, and an outer area. Each aircraft
must establish two-way radio communications with the
ATC facility providing air traffic services prior to entering
the airspace and thereafter maintain those communications
while within the airspace.

Class D Airspace
Class D airspace is generally airspace from the surface to
2,500 feet above the airport elevation (charted in MSL)
surrounding those airports that have an operational control
tower. The configuration of each Class D airspace area is
individually tailored and when instrument procedures are
published, the airspace is normally designed to contain the
procedures. Arrival extensions for instrument approach
procedures (IAPs) may be Class D or Class E airspace. Unless
otherwise authorized, each aircraft must establish two-way
radio communications with the ATC facility providing air
traffic services prior to entering the airspace and thereafter
maintain those communications while in the airspace.

Class E Airspace
If the airspace is not Class A, B, C, or D, and is controlled
airspace, then it is Class E airspace. Class E airspace extends
upward from either the surface or a designated altitude to the
overlying or adjacent controlled airspace. When designated
as a surface area, the airspace is configured to contain all
instrument procedures. Also in this class are federal airways,
airspace beginning at either 700 or 1,200 feet above ground
level (AGL) used to transition to and from the terminal or
en route environment, and en route domestic and offshore
airspace areas designated below 18,000 feet MSL. Unless
designated at a lower altitude, Class E airspace begins at
14,500 MSL over the United States, including that airspace
overlying the waters within 12 NM of the coast of the 48
contiguous states and Alaska, up to but not including 18,000
feet MSL, and the airspace above FL 600.