6/17/21 

Pilot/Controller Glossary 

CONTROLLED AIRSPACE

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 An airspace of 

defined dimensions within which air traffic control 
service is provided to IFR flights and to VFR flights 
in accordance with the airspace classification. 

a. 

Controlled airspace is a generic term that covers 

Class A, Class B, Class C, Class D, and Class E 
airspace. 

b. 

Controlled airspace is also that airspace within 

which all aircraft operators are subject to certain pilot 
qualifications, operating rules, and equipment 
requirements  in  14 CFR Part 91 (for specific 
operating requirements, please refer to 14 CFR 
Part 91). For IFR operations in any class of controlled 
airspace, a pilot must file an IFR flight plan and 
receive an appropriate ATC clearance. Each Class B, 
Class C, and Class D airspace area designated for an 
airport contains at least one primary airport around 
which the airspace is designated (for specific 
designations and descriptions of the airspace classes, 
please refer to 14 CFR Part 71). 

c. 

Controlled airspace in the United States is 

designated as follows: 

1. 

CLASS A

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  Generally, that airspace from 

18,000 feet MSL up to and including FL 600, 
including the airspace overlying the waters within 12 
nautical miles of the coast of the 48 contiguous States 
and Alaska. Unless otherwise authorized, all persons 
must operate their aircraft under IFR. 

2. 

CLASS B

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 Generally, that airspace from the 

surface to 10,000 feet MSL surrounding the nation’s 
busiest airports in terms of airport operations or 
passenger enplanements. The configuration of each 
Class B airspace area is individually tailored and 
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. The cloud clearance requirement for VFR 
operations is “clear of clouds.” 

3. 

CLASS C

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 Generally, that 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 that have a certain 
number of IFR operations or passenger enplane-

ments. Although the configuration of each Class C 
area is individually tailored, the airspace usually 
consists of a surface area with a 5 NM radius, a circle 
with a 10 NM radius that extends no lower than 1,200 
feet up to 4,000 feet above the airport elevation, and 
an outer area that is not charted. Each person 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. VFR 
aircraft are only separated from IFR aircraft within 
the airspace. 

(See OUTER AREA.) 

4. 

CLASS D

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 Generally, that 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 will normally be designed to contain the 
procedures. Arrival extensions for instrument 
approach procedures may be Class D or Class E 
airspace. Unless otherwise authorized, each person 
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. No separation 
services are provided to VFR aircraft. 

5. 

CLASS E

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 Generally, if the airspace is not 

Class A, Class B, Class C, or Class D, and it is 
controlled airspace, 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 will be configured to contain all 
instrument procedures. Also in this class are Federal 
airways, airspace beginning at either 700 or 1,200 
feet AGL used to transition to/from the terminal or en 
route environment, 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 nautical miles 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. 

CONTROLLED AIRSPACE [ICAO]

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 An airspace 

of defined dimensions within which air traffic control 

PCG C

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