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AIM

10/12/17

5−3−1

En Route Procedures

Section 3. En Route Procedures

5−3−1. 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−

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−out

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−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 5−3−1 through TBL 5−3−19, CPDLC Message

Elements, below.

NOTE−

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−

(Aircraft identification) contact (facility name or location

name and terminal function) (frequency) at (time, fix, or

altitude).
NOTE−

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.

9/13/18

AIM