User's Guide

User Guide for the Envoy Data Link
Document Number: UG-15000 Rev. A Page 26 of 173
3 CPDLC Operations
CPDLC messages for both FANS and ATN can be viewed as two-way conversations that comprise
a ground control instruction (uplink message, or UM) from an ATSU or a pilot request (downlink
message, or DM) and required responses to close the communication transaction.
A transaction may comprise up to 5 elements (uplink or downlink messages and responses) and
may queue one or more reports based on event, time, or repeat interval settings specified in the
original message.
The Envoy provides robust support of CPDLC message exchange with requests, predictive
responses, report management, message validation, and preformatted free text messages to
simplify pilot workload. Report management includes one-time, event-driven, or continuous interval
reporting that can be easily viewed and edited from the queued report listing.
CPDLC message exchanges are captured in a message log that displays the dynamic transition
from NEW to SENDING, and then to OPEN when an automated ground network system (AGNS)
acknowledgement is received, and finally CLOSED when the response and acknowledgement
have been met. All messages in the Envoy message logs are identified by type (U=uplink,
D=downlink), timestamp, and message summary, and aircrew has the option of removing closed
messages from the log, printing individual messages or the printing the entire message log, as
desired.
3.1 Log On
The Envoy uses Data Link Initiation Capability (DLIC) to register the aircraft with an ATSU and to
initiate data link communications. An ATC logon must be initialized manually by the aircrew:
• At or after departure
• When entering an airspace that has data link service from an airspace that does not
• When entering an airspace that has a different data link service (FANS to ATN or ATN to FANS)
• Following a failed data link transition to the next data authority (NDA)
• As instructed by an ATSU
An ATC LOGON registers the aircraft on the data link service network and associates the aircraft
with flight plan data (such as departure and arrival airports), which facilitates automatic handoffs to
ATSUs on the route. The logon request provides also provides the ATSU with information about
the data link applications supported by the aircraft (ATN CPDLC, FANS CPDLC, ADS-C,
SATCOM) and version numbers for those applications
An ATSU can set up an ADS-C connection (i.e., for a single demand contract) without establishing
a logon session.
There are two logon sequences, AFN (FANS) and CM (ATN). The following subsections detail the
CM logon and ATN CPDLC.
3.1.1 Aircrew LOGON Request
There are three parts to activating a CPDLC session:
• VHF connection must be available, as shown at LSK R5 (DLK STATUS: AVAIL).
• Pilot must input a valid ATSU ID at LSK L1 by pressing LSK R6 (LOGON TO)
• The ATSU responds with a connection request, and the Envoy automatically confirms the CPDLC
connection