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facilities. Several thousand pieces of maintainable
equipment including radar, communications switches,
ground-based navigation aids, computer displays, and
radios are used in NAS operations, and NAS components represent billions of dollars in investments by the
government. Additionally, the aviation industry has
invested significantly in ground facilities and avionics
systems designed to use the NAS. Approximately
47,000 FAA employees provide air traffic control, flight
service, security, field maintenance, certification, system acquisition, and other essential services.
Differing levels of ATC facilities vary in their structure and purpose. Traffic management at the national
level is led by the Command Center, which essentially “owns” all airspace. Regional Centers, in turn,
sign Letters of Agreement (LOAs) with various
approach control facilities, delegating those facilities
chunks of airspace in which that approach control
facility has jurisdiction. The approach control facilities, in turn, sign LOAs with various towers that are
within that airspace, further delegating airspace and
Figure 1-8. Increasing use of regional jets is expected to have
a significant impact on traffic.
1-10
responsibility. This ambiguity has created difficulties
in communication between the local facilities and the
Command Center. However, a decentralized structure
enables local flexibility and a tailoring of services to
meet the needs of users at the local level. Improved
communications between the Command Center and
local facilities could support enhanced safety and
efficiency while maintaining both centralized and
decentralized aspects to the ATC system.
AIR ROUTE TRAFFIC CONTROL CENTER
A Center’s primary function is to control and separate
air traffic within a designated airspace, which may cover
more than 100,000 square miles, may span several
states, and extends from the base of the underlying controlled airspace up to Flight Level (FL) 600. There are
21 Centers located throughout the U.S., each of which is
divided into sectors. Controllers assigned to these sectors, which range from 50 to over 200 miles wide, guide
aircraft toward their intended destination by way of vectors and/or airway assignment, routing aircraft around
weather and other traffic. Centers employ 300 to 700
controllers, with more than 150 on duty during peak
hours at the busier facilities. A typical flight by a commercial airliner is handled mostly by the Centers.
TERMINAL RADAR APPROACH CONTROL
Terminal Radar Approach Control (TRACON) controllers work in dimly lit radar rooms located within
the control tower complex or in a separate building
located on or near the airport it serves. [Figure 1-9]
Using radarscopes, these controllers typically work
an area of airspace with a 50-mile radius and up to an
altitude of 17,000 feet. This airspace is configured to
provide service to a primary airport, but may include
other airports that are within 50 miles of the radar
service area. Aircraft within this area are provided
vectors to airports, around terrain, and weather, as
well as separation from other aircraft. Controllers in
TRACONs determine the arrival sequence for the control tower’s designated airspace.
CONTROL TOWER
Controllers in this type of facility manage aircraft operations on the ground and within specified airspace
around an airport. The number of controllers in the
tower varies with the size of the airport. Small general
aviation airports typically have three or four controllers, while larger international airports can have up
to fifteen controllers talking to aircraft, processing
flight plans, and coordinating air traffic flow. Tower
controllers manage the ground movement of aircraft
around the airport and ensure appropriate spacing
between aircraft taking off and landing. In addition, it
is the responsibility of the control tower to determine
the landing sequence between aircraft under its control. Tower controllers issue a variety of instructions to
pilots, from how to enter a pattern for landing to how
to depart the airport for their destination.
FLIGHT SERVICE STATIONS
Flight Service Stations (FSSs) and Automated Flight
Service Stations (AFSSs) are air traffic facilities which
provide pilot briefings, en route communications and
VFR search and rescue services, assist lost aircraft and
aircraft in emergency situations, relay ATC clearances,
originate Notices to Airmen, broadcast aviation weather
and NAS information, receive and process IFR flight
plans, and monitor navigational aids (NAVAIDs). In addition, at selected locations, FSSs/AFSSs provide En route
　
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