Page 129 - Planning and Design of Airports

98 Airp o r t Pl anning

Each ARTCC geographical area is divided into sectors. The con-
figuration of each sector is based on equalizing the workload of the
controllers. Control of aircraft is passed from one sector to another.
The geographical area is sectored not only in the horizontal but also
in the vertical plane. Thus there can be a high-altitude sector above
one or more low-altitude sectors. Each sector is manned by one or
more controllers, depending on the volume and complexity of traffic.
The average number of aircraft that each sector can handle depends
on the number of people assigned to the sector, the complexity of traf-
fic, and the degree of automation provided.
Each sector is normally provided with one or more air route sur-
veillance radar (ARSR) units which cover the entire sector and allow
for monitoring of separation between aircraft in the sector. In addi-
tion, each sector has information on the identification of the aircraft,
destination, flight plan route, estimated speed, and flight altitude,
which is posted on pieces of paper called flight progress strips, and
are superimposed on the radarscope adjacent to the blips which iden-
tify the position and identity of aircraft. The strips are continuously
updated as the need arises.
At present, communication between the pilot and controller is by
voice. Therefore each ARTCC is assigned a number of VHF and UHF
radio communication frequencies. The controller in turn assigns a
specific frequency to the pilot. However, modernization of air traffic
control is planned to include further proliferation of digital commu-
nications, known as controller pilot data link communications
(CPDLC) between controllers and pilots.

Terminal Approach Control Facilities
The terminal approach control facility (TRACON) monitors the air traf-
fic in the airspace surrounding airports with moderate to high density
traffic. It has jurisdiction in the control and separation of air traffic from
the boundary area of the air traffic control tower at an airport to a dis-
tance of up to 50 mi from the airport and to an altitude ranging up to
17,000 ft. This is commonly referred to as the terminal area. Where there
are several airports in an urban area, one facility may control traffic to all
of these airports. In essence the facility receives aircraft from the ARTCC
and guides them to one of several airports. In providing this guidance, it
performs the important function of metering and sequencing aircraft to
provide uniform and orderly flow to the airports.
The organizational structure of an approach control facility is very
similar to the ARTCC. Like the ARTCC, the geographic area of the facil-
ity is divided into sectors to equalize the workload of the controllers. The
approach control facility transfers control of an arriving aircraft to the
airport control tower when it is lined up with the runway about 5 mi
from the airport. Likewise, control of departing aircraft is transferred to
the approach control facility by the airport control tower.