Introduction
The two categories of airspace are: regulatory and
nonregulatory. Within these two categories, there are four
types: controlled, uncontrolled, special use, and other
airspace. The categories and types of airspace are dictated
by the complexity or density of aircraft movements, nature
of the operations conducted within the airspace, the level of
safety required, and national and public interest. Figure 15-1
presents a profile view of the dimensions of various classes
of airspace. Also, there are excerpts from sectional charts
that are discussed in Chapter 16, Navigation, that are used
to illustrate how airspace is depicted.
Airspace
Chapter 15
14,500' MSL
Nontowered
airport with
instrument
approach
Nontowered
airport with
no instrument
approach
700'
AGL700'
AGL
18,000' MSL
FL 600
1,200'
AGL
700'
AGL
1,200'
AGL
1,200'
AGL
Class
A
Class
B
Class
C
Class
D
Class
E
Class
G
Class
G
Class
G
Class
G
Figure 15-1. Airspace profile.
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 enplanements. 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. 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. Each aircraft must establish two-way radio
communications with the ATC facility providing air traffic
services prior to entering the airspace and thereafter must
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
Class E airspace is the controlled airspace not classified as
Class A, B, C, or D airspace. A large amount of the airspace
over the United States is designated as Class E airspace.
Figure 15-2. An example of a prohibited area, P-40 around Camp
David.
This provides sufficient airspace for the safe control and
separation of aircraft during IFR operations. Chapter 3 of
the Aeronautical Information Manual (AIM) explains the
various types of Class E airspace.
Sectional and other charts depict all locations of Class E
airspace with bases below 14,500 feet MSL. In areas where
charts do not depict a class E base, class E begins at 14,500
feet MSL.
In most areas, the Class E airspace base is 1,200 feet AGL. In
many other areas, the Class E airspace base is either the surface
or 700 feet AGL. Some Class E airspace begins at an MSL
altitude depicted on the charts, instead of an AGL altitude.
Class E airspace typically extends up to, but not including,
18,000 feet MSL (the lower limit of Class A airspace). All
airspace above FL 600 is Class E airspace.
Uncontrolled Airspace
Class G Airspace
Uncontrolled airspace or Class G airspace is the portion of
the airspace that has not been designated as Class A, B, C,
D, or E. It is therefore designated uncontrolled airspace.
Class G airspace extends from the surface to the base of the
overlying Class E airspace. Although ATC has no authority
or responsibility to control air traffic, pilots should remember
there are visual flight rules (VFR) minimums that apply to
Class G airspace.
Special Use Airspace
Special use airspace or special area of operation (SAO)
is the designation for airspace in which certain activities
must be confined, or where limitations may be imposed
on aircraft operations that are not part of those activities.
Certain special use airspace areas can create limitations on
the mixed use of airspace. The special use airspace depicted
on instrument charts includes the area name or number,
effective altitude, time and weather conditions of operation,
the controlling agency, and the chart panel location. On
National Aeronautical Charting Group (NACG) en route
charts, this information is available on one of the end panels.
Special use airspace usually consists of:
• Prohibited areas
• Restricted areas
• Warning areas
• Military operation areas (MOAs)
• Alert areas
• Controlled firing areas (CFAs)
Prohibited Areas
Prohibited areas contain airspace of defined dimensions
within which the flight of aircraft is prohibited. Such areas
are established for security or other reasons associated with
the national welfare. These areas are published in the Federal
Register and are depicted on aeronautical charts. The area is
charted as a “P” followed by a number (e.g., P-40). Examples
of prohibited areas include Camp David and the National
Mall in Washington, D.C., where the White House and the
Congressional buildings are located. [Figure 15-2]
Restricted Areas
Restricted areas are areas where operations are hazardous to
nonparticipating aircraft and contain airspace within which
the flight of aircraft, while not wholly prohibited, is subject
to restrictions. Activities within these areas must be confined
because of their nature, or limitations may be imposed upon
aircraft operations that are not a part of those activities, or
both. Restricted areas denote the existence of unusual, often
invisible, hazards to aircraft (e.g., artillery firing, aerial
gunnery, or guided missiles). IFR flights may be authorized
to transit the airspace and are routed accordingly. Penetration
of restricted areas without authorization from the using
or controlling agency may be extremely hazardous to the
aircraft and its occupants. ATC facilities apply the following
procedures when aircraft are operating on an IFR clearance
(including those cleared by ATC to maintain VFR on top) via
a route that lies within joint-use restricted airspace:
1. If the restricted area is not active and has been released
to the Federal Aviation Administration (FAA), the
ATC facility allows the aircraft to operate in the
restricted airspace without issuing specific clearance
for it to do so.
2. If the restricted area is active and has not been released
to the FAA, the ATC facility issues a clearance that
ensures the aircraft avoids the restricted airspace.