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International (BDL) airspace, such as Hartford (HFD).
[Figure 9-10]
A valuable service provided by the automated radar
equipment at terminal radar facilities is the Minimum Safe
Altitude Warnings (MSAW). This equipment predicts an
aircraft’s position in 2 minutes based on present path of
flight—the controller issues a safety alert if the projected
path encounters terrain or an obstruction. An unusually
rapid descent rate on a nonprecision approach can trigger
such an alert.
Air Route Traffic Control Center (ARTCC)
ARTCC facilities are responsible for maintaining separation
between IFR flights in the en route structure. Center radars
(Air Route Surveillance Radar (ARSR)) acquire and track
transponder returns using the same basic technology as
terminal radars. [Figure 9-11]
Earlier Center radars display weather as an area of slashes
(light precipitation) and Hs (moderate rainfall), as illustrated
in Figure 9-12. Because the controller cannot detect higher
levels of precipitation, pilots should be wary of areas showing
moderate rainfall. Newer radar displays show weather as
three levels of blue. Controllers can select the level of weather
to be displayed. Weather displays of higher levels of intensity
can make it difficult for controllers to see aircraft data blocks,
so pilots should not expect ATC to keep weather displayed
continuously.
Center airspace is divided into sectors in the same manner
as terminal airspace; additionally, most Center airspace is
divided by altitudes into high and low sectors. Each sector
has a dedicated team of controllers and a selection of radio
frequencies, because each Center has a network of remote
transmitter/receiver sites. All Center frequencies can be found
in the back of the A/FD in the format shown in Figure 9-13;
they are also found on en route charts.
Each ARTCC’s area of responsibility covers several states;
when flying from the vicinity of one remote communication
site toward another, expect to hear the same controller on
different frequencies.
Center Approach/Departure Control
The majority of airports with instrument approaches do not
lie within terminal radar airspace, and when operating to
or from these airports pilots communicate directly with the
Center controller. Departing from a tower-controlled airport,
the tower controller provides instructions for contacting the
appropriate Center controller. When departing an airport
without an operating control tower, the clearance includes
instructions such as “Upon entering controlled airspace,
contact Houston Center on 126.5.” Pilots are responsible
for terrain clearance until reaching the controller’s MVA.
Simply hearing “Radar contact” does not relieve a pilot of
this responsibility.
If obstacles in the departure path require a steeper-thanstandard
climb gradient (200 FPNM), then the controller
advises the pilot. However, it is the pilot’s responsibility to
check the departure airport listing in the A/FD to determine if
there are trees or wires in the departure path. When in doubt,
ask the controller for the required climb gradient.
9-8
Figure 9-9. The top image is a display as seen by controllers in an Air Traffic Facility. The one illustrated is an ARTS III (Automated
Radar Terminal System). The display shown provides an explanation of the symbols in the graphic. The lower figure is an example of
the Digital Bright Radar Indicator Tower Equipment (DBRITE) screen as seen by tower personnel. It provides tower controllers with
a visual display of the airport surveillance radar, beacon signals, and data received from ARTS III. The display shown provides an
explanation of the symbols in the graphic.
9-9
Figure 9-10. A Portion of the New York Area Tower En Route List. (From the A/FD)
9-10
Figure 9-11. Center Radar Displays. Figure 9-12. A Center Controller’s Scope.
Figure 9-13. Center Symbology.
A common clearance in these situations is “When able,
proceed direct to the Astoria VOR…” The words “when able”
mean to proceed to the waypoint, intersection, or NAVAID
when the pilot is able to navigate directly to that point using
onboard available systems providing proper guidance, usable
signal, etc. If provided such guidance while flying VFR, the
pilot remains responsible for terrain and obstacle clearance.
Using the standard climb gradient, an aircraft is 2 miles
from the departure end of the runway before it is safe to
turn (400 feet above ground level (AGL)). When a Center
controller issues a heading, a direct route, or says “direct
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