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Instrument Flying Handbook
The Air Traffic Control System
Communication Procedures and Facilities

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

The aircraft appears on the controller's radar display as a
target with an associated data block that moves as the aircraft
moves through the airspace. The data block includes aircraft
identification, aircraft type, altitude, and airspeed.

A TRACON controller uses Airport Surveillance Radar
(ASR) to detect primary targets and Automated Radar
Terminal Systems (ARTS) to receive transponder signals, the
two are combined on the controller's scope. [Figure 9-9]

At Facilities with ASR-3 equipment, radar returns from
precipitation are not displayed as varying levels of intensity,
and controllers must rely on pilot reports and experience
to provide weather avoidance information. With ASR-9
equipment, the controller can select up to six levels of
intensity. Light precipitation does not require avoidance
tactics but precipitation levels of moderate, heavy or
extreme should cause pilots to plan accordingly. Along
with precipitation the pilot must additionally consider the
temperature, which if between -20° and +5°C will cause icing
even during light precipitation. The returns from higher levels
of intensity may obscure aircraft data blocks, and controllers
may select the higher levels only on pilot request. When
uncertainty exists about the weather ahead, ask the controller
if the facility can display intensity levels, pilots of small
aircraft should avoid intensity levels 3 or higher.

Tower En Route Control (TEC)
At many locations, instrument flights can be conducted
entirely in terminal airspace. These TEC routes are generally
for aircraft operating below 10,000 feet, and they can be
found in the A/FD. Pilots desiring to use TEC should include
that designation in the remarks section of the flight plan.

Pilots are not limited to the major airports at the city pairs
listed in the A/FD. For example, a tower en route flight from
an airport in New York (NYC) airspace could terminate
at any airport within approximately 30 miles of Bradley
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

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-than-
standard 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.