AIM

4/3/14

5−3−1

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. As a result, it expands

two−way air traffic control air/ground communica-

tions capabilities. Consequently, the air traffic

system’s operational capacity is increased and any

associated air traffic delays become minimized. A

related safety benefit is that pilot/controller read−

back and hear−back errors will be significantly

reduced. 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)

CPDLC Build 1 offers four ATC data link

services. These are altimeter setting (AS), transfer of

communications (TC), initial contact (IC), and menu

text messages (MT).

(1)

Altimeter settings are usually trans-

mitted automatically when a CPDLC session and

eligibility has been established with an aircraft. 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 ATC host

computer stored altitude. If an altitude mismatch is

detected, the controller will verbally provide

corrective action.

(3)

Transfer of communications automati-

cally establishes data link contact with a succeeding

sector.

(4)

Menu text transmissions are scripted

nontrajectory altering uplink messages.

NOTE

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Initial use of CPDLC will be at the Miami Air Route Traffic
Control Center (ARTCC). Air carriers will be the first
users. Subsequently, CPDLC will be made available to all
NAS users. Later versions will include trajectory altering
services and expanded clearance and advisory message
capabilities.

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.