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| The various air traffic control facilities encountered by a plane during its flight |
Departure, En Route and Descent
Once your plane takes off, your pilot activates a transponder device inside the aircraft. The transponder detects incoming radar signals and broadcasts an amplified, encoded radio signal
in the direction of the detected radar wave. The transponder signal
provides the controller with your aircraft's flight number, altitude,
airspeed and destination. A blip representing the airplane appears on
the controller's radar screen with this information beside it. The
controller can now follow your plane.
An airplane's transponder transmits flight data to incoming radar signals.
The departure controller
is located in the TRACON facility, which may have several airports
within its airspace (50-mile/80-km radius). He or she uses radar to
monitor the aircraft and must maintain safe distances between ascending
aircraft. The departure controller gives instructions to your pilot
(heading, speed, rate of ascent) to follow regular ascent corridors through the TRACON airspace.
The
departure controller monitors your flight during ascent to the en route
portion. When your plane leaves TRACON airspace, the departure
controller passes your plane off to the center controller
(ARTCC controller). Every time your plane gets passed between
controllers, an updated flight progress slip gets printed and
distributed to the new controller.
En Route and Descent
Once
your plane has left TRACON airspace, it enters a sector of the ARTCC
airspace, where it is monitored by at least two air traffic controllers.
The radar associate controller receives the
flight-plan information anywhere from five to 30 minutes prior to your
plane entering that sector. The associate controller works with the
radar controller in charge of that sector. The radar controller
is in charge of all air-to-ground communication, maintains safe
separation of aircraft within the sector and coordinates activities with
other sectors and/or centers. The controllers must monitor the airspace
at high altitude (above 24,000 ft/7320 m) and low altitude (below
24,000 ft). The center controllers provide your pilot with updated
weather and air-traffic information. They also give directions to your
pilot regarding such aspects as speed and altitude to maintain a safe
separation between aircraft within their sector. They monitor your plane
until it leaves their sector. Then they pass it off to another sector's
controller.
Another controller, called the radar hand-off controller,
assists the radar and associate radar controllers during times of heavy
traffic, watching the radar screen and helping to maintain smooth
air-traffic flow.
While you are enjoying your meal, snack,
in-flight movie or the view outside the window, your plane gets passed
from sector to sector and center to center. In each sector, center
controllers radio instructions to the pilots. The path of your plane may
have to be changed from the original flight plan to move around bad
weather or avoid a congested sector. Your pilots may request a change in
altitude to avoid or reduce turbulence. This back and forth between
pilots and center controllers continues until you are about 150 miles
(241 km) from San Francisco (your destination). At this point, the
center controller directs all planes flying into San Francisco to move
from high altitudes to low altitudes and merges the descending aircraft
into a single file line toward the airport. The controller gives
instructions to your pilot, such as changes in heading, speed and
altitude, to place your plane in line with these other aircraft.
Depending on traffic conditions, the controller may have to place your
plane into a holding pattern, which is a standard route around each
airport, where you wait until the airport can handle your arrival. The
controller continues to give directions to your pilot until your plane
is within TRACON airspace.
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