Class B airspace surrounds the nation's busiest airports and airport hubs in cities like Boston, Chicago, and Los Angeles
Class B airspace is designed to help
manage the flow of high volumes of airline traffic as these aircraft descend from the high-altitude flight levels into the
lower altitudes and eventually the airport itself. It also helps manage their departure. The airspace is shaped like an upside-down
wedding cake to help funnel aircraft in and out of the main airport.
Most Class B airspace extends from
the surface to 10,000 feet MSL with a circular diameter of 40 nautical miles.
Pilots must obtain a clearance from
air traffic control (ATC) before entering Class B airspace and then maintain radio contact with ATC. Aircraft must be equipped
with an altitude-encoding transponder.
Pilots must hold at least a private
pilot certificate to enter. Or, a sport, recreational, or student certificate if certain advanced training requirements are
met — although many Class B airports prohibit any student pilot solo flights.
An instrument rating is not required;
pilots may operate under visual flight rules (VFR) in Class B airspace as long as they remain clear of the clouds and have
at least three miles of in-flight visibility.
Class C airspace surrounds other busy airports that have radar services for arriving and departing aircraft. Typical airports
with Class C airspace would be Providence, Nashville, or Sacramento.
Most Class C airspace extends from
the surface to 4,000 feet above ground level (agl), with a circular diameter of 20 nautical miles.
An air traffic control (ATC) clearance
is not required in Class C airspace, but pilots must be in radio communication with ATC, and aircraft must be equipped with
an altitude-encoding transponder. There are no additional pilot qualifications for operating in Class C, D, E, or G airspace.
Pilots flying under visual flight
rules (VFR) in Class C airspace must have at least three miles of visibility. They also must maintain a specified distance
from the clouds.
Class D airspace surrounds airports with operating control towers and weather reporting service that are not superseded by
more restrictive Class B or C airspace.
Most Class D airspace extends from
the surface to 2,500 feet above ground level (agl), with a circular diameter of 4.3 nautical miles (5 statute miles).
Aircraft must establish and maintain
two-way radio contact with the control tower before entering or operating in Class D airspace. Weather minimums are the same
as for Class C airspace.
Class E airspace includes all other
controlled airspace in the United States. The upper limit of Class E airspace is 18,000 feet mean sea level (msl). However,
the lower limit (where it starts) can be 14,500 feet msl, 10,000 feet msl, 1,200 feet above ground level (agl), 700 feet agl,
or all the way to the surface of the Earth.
Most nonairport or nonairway Class
E airspace located east of the Rocky Mountains starts at 1,200 feet agl, dropping lower over some airports. Most of the Class
E airspace west of the Rocky Mountains starts at 10,000 feet or 14,500 feet msl.
The Class E airspace above 10,000
feet msl has greater visibility and cloud clearance minimums for visual flight rules (VFR) operations.
Class E airspace also surrounds airports
that have weather reporting services in support of instrument flight rules (IFR) operations, but no operating control tower.
Weather minimums for these areas of Class E airspace are the same as for Class C and D airspace.
All victor airways that are not part
of a higher class of airspace are Class E airspace.
Class F airspace is not
used in the United States.
Class G airspace is uncontrolled,
so it includes all airspace in the United States that is not classified as Class A, B, C, D, or E.
No air traffic control (ATC) services
are provided, and the only requirement for flight is certain visibility and cloud clearance minimums.
Most of the airspace up to 1,200
feet above ground level (agl) is Class G airspace. There is virtually no Class G airspace above 1,200 feet agl east of the
Special Use Airspace
Special use airspace (SUA) includes prohibited areas, restricted
areas, warning areas, military operations areas (MOAs), alert areas, and controlled firing areas.
In these areas, aeronautical activity
must be limited, usually because of military use or national security concerns.
You can see most standard SUAs with our interactive airspace
Other Airspace Areas
Other airspace areas include airport advisory
areas, military training routes, and areas where temporary flight restrictions (TFRs) or limitations/prohibitions apply. For
example, TFRs are often established over large forest fires to help keep aircraft from straying into hazardous conditions.
Smaller TFRs are issued for presidential movements, some large sporting events, and more.