National Airspace System

The National Airspace System (NAS) of the United States is one of the most complex aviation systems in the world — consisting of thousands of people, procedures, facilities, and pieces of equipment — that enables safe and expeditious air travel in the United States and over large portions of the world's oceans.

The NAS requires approximately 14,500 air traffic controllers, 4,500 aviation safety inspectors, and 5,800 technicians to operate and maintain services. It has more than 19,000 airports and 600 air traffic control facilities. In all, there are 41,000 NAS operational facilities. In addition, there are over 71,000 pieces of equipment, ranging from radar systems to communication relay stations. On average, about 50,000 flights use NAS services each day.

Airspace Classification

Controlled Airspace

In the United States, airspace consists of Classes Alpha, Bravo, Charlie, Delta, Echo, and Golf. [1]

Class Alpha begins and includes 18,000 ft. MSL and continues up to 60,000 ft. MSL. It is the most controlled airspace and requires a pilot to carry an Instrument Flight Rating and proper clearance no matter what type of aircraft is being flown. Pilots are also required to change their altimeter settings to 29.92 in. to ensure all pilots within the airspace have the same readings. This ensures proper altitude separation.

Class Bravo airspace extends from the surface up to 10,000 ft. AGL and is the area above and around the busiest airports (LAX, JAX, CVG) and is also heavily controlled. A side view of class B airspace resembles an upside-down wedding cake with 3 layers becoming bigger toward the top. Class B's are designed individually to meet the needs of the airport they overlay. Pilots must also receive clearance to enter the class B airspace but Visual Flight Reference may be used.

Class Charlie airspace reaches from the surface to 4000 ft. AGL above the airport which the surround. Class C airspace only exists over airports which have an operational control tower, are serviced by a radar approach control, and have a certain number of Instrument flight operations. Class C is also individually designed for airports but usually covers a surface area of about 5 nautical miles around the airport up until 1200 ft AGL. At 1200 ft. the airspace extends to 10 nautical miles in diameter which continues to 4000 ft. Pilots are required to establish two-way radio communications with the ATC facility providing air traffic control service to the area before entering the airspace. Within Class C, Visual and Instrument pilots are separated.

Class Delta airspace exists from the surface to 2500 ft. AGL above the airport. Class D airspace only surrounds airports with an operational control tower. Class D airspace is also tailored to meet the needs of the airport. Pilots are required to establish and maintain two-way radio communications with the ATC facility providing air traffic control services prior to entering the airspace. Pilots using Visual Flight Reference must be vigilant for traffic as there is no separation service in the airspace.

Class Echo airspace is the airspace that lies between Classes A, B, C, and D. Class E extends from either the surface or the roof of the underlying airspace and ends at the floor of the controlled airspace above. Class E exists for those planes transitioning from the terminal to en route state. It also exists as an area for Instrument pilots to remain under ATC control without flying in a controlled airspace. Under Visual Flight Conditions, Class E can be considered uncontrolled airpace.

Non-Controlled Airspace

Airports without operational control towers are uncontrolled airfields. Pilots in these areas are responsible for position and separation using a specified CTAF or Common Traffic Advisory Frequency for that airport.

Class Golf airspace is completely uncontrolled airspace which extends from the surface to either 700 or 1200 ft. AGL depending on the floor of the overlying Class Echo. CTAF is the only frequency used for radio communication among pilots. No towers or in-flight control services are used.

See also

• Acronyms and abbreviations in avionics

External links

• IFR Operations in the National Airspace System