AIM

8/15/19

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En Route Procedures

Section 3. En Route Procedures

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1. ARTCC Communications

a. Direct Communications, Controllers and

Pilots.

1.

ARTCCs are capable of direct communica-

tions with IFR air traffic on certain frequencies.
Maximum communications coverage is possible
through the use of Remote Center Air/Ground
(RCAG) sites comprised of both VHF and UHF
transmitters and receivers. These sites are located
throughout the U.S. Although they may be several
hundred miles away from the ARTCC, they are
remoted to the various ARTCCs by land lines or
microwave links. Since IFR operations are expedited
through the use of direct communications, pilots are
requested to use these frequencies strictly for
communications pertinent to the control of IFR
aircraft. Flight plan filing, en route weather, weather
forecasts, and similar data should be requested
through FSSs, company radio, or appropriate military
facilities capable of performing these services.

2.

An ARTCC is divided into sectors. Each

sector is handled by one or a team of controllers and
has its own sector discrete frequency. As a flight
progresses from one sector to another, the pilot is
requested to change to the appropriate sector discrete
frequency.

3.

Controller Pilot Data Link Communications

(CPDLC) is a system that supplements air/ground
voice communications. The CPDLC’s principal
operating criteria are:

(a)

Voice remains the primary and controlling

air/ground communications means.

(b)

Participating aircraft will need to have the

appropriate CPDLC avionics equipment in order to
receive uplink or transmit downlink messages.

(c)

En Route CPDLC Initial Services offer the

following services: Altimeter Setting (AS), Transfer
of Communications (TOC), Initial Contact (IC), and
limited route assignments, including airborne
reroutes (ABRR), limited altitude assignments, and
emergency messages.

(1)

Altimeter settings will be uplinked

automatically when appropriate after a Monitor TOC.

Altimeter settings will also be uplinked automatically
when an aircraft receives an uplinked altitude
assignment below FL 180. A controller may also
manually send an altimeter setting message.

NOTE

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When conducting instrument approach procedures, pilots
are responsible to obtain and use the appropriate altimeter
setting in accordance with 14 CFR Section 97.20. CPDLC
issued altimeter settings are excluded for this purpose.

(2)

Initial contact is a safety validation

transaction that compares a pilot’s initiated altitude
downlink message with an aircraft’s stored altitude in
the ATC automation system. When an IC mismatch or
Confirm Assigned Altitude (CAA) downlink time

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indicator is displayed in the Full Data Block (FDB)
and Aircraft List (ACL), the controller who has track
control of the aircraft must use voice communication
to verify the assigned altitude of the aircraft, and
acknowledge the IC mismatch/time

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out indicator.

(3)

Transfer of communications automati-

cally establishes data link contact with a succeeding
sector.

(4)

Menu text transmissions are scripted

nontrajectory altering uplink messages.

(5)

The CPDLC Message Elements for the

Initial Capabilities rollout are contained in
TBL 5

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1 through TBL 5

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19, CPDLC Message

Elements, below.

NOTE

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The FAA is not implementing ATN B1; the ATN B1 column
in the tables is there for informational purposes only.

b. ATC Frequency Change Procedures.

1.

The following phraseology will be used by

controllers to effect a frequency change:

EXAMPLE

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(Aircraft identification) contact (facility name or location
name and terminal function) (frequency) at (time, fix, or
altitude).

NOTE

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Pilots are expected to maintain a listening watch on the
transferring controller’s frequency until the time, fix, or
altitude specified. ATC will omit frequency change
restrictions whenever pilot compliance is expected upon
receipt.