User's Guide

User Guide for the Envoy Data Link
Document Number: UG-15000 Rev. A Page 31 of 173
• If in the same DSP (FANS or ATN), the Envoy is automatically aborts any open messages with the
CDA and transitions the session to the CDA
• If the transition involves changing DSP (i.e., from FANS to ATN, or ATN to FANS), any open
message transactions are aborted, the scratchpad displays an advisory message: TERMINATED,
and the aircrew must conduct a logon procedure. The Envoy displays the NDA ATSU ID in the
LOGON TO field.
Terminate All Services Uplink
When the current data authority uplinks a TERMINATE ALL SERVICES:
• In FANS, any open message transactions and queued reports are aborted and the CPDLC session
is terminated immediately
• In ATN, a WILCO response to either uplink message terminates the CPDLC session.
The scratchpad displays an advisory message: TERMINATED; this advisory message is not saved
to a message log.
3.3 Lost Connection
If the connection to the CDA is lost, all open/pending messages are aborted, and the aircrew will
need to logon again.
3.4 Typical Message Composition
This section identifies the transaction dialog for aircrew-initiated requests and ground-station-
initiated instructions and requests, which may include queued reports based on event triggers.
The Envoy recognizes message structure and intuitively constructs downlink message prompts
from keywords. For example, the Envoy intuitively predicts required input fields for a downlink
response and constructs responses in accordance with ICAO GOLD, RTCA FANS, and ATN
interoperability requirements.
If an uplink message contains a report request, the Envoy formats a response that queues an
event-driven report to automatically downlink when the when the criteria are met. The Envoy can
track up to 10 queued reports.
Free text entered in the scratchpad that exceeds 24 characters per line automatically advances to
fill the available lines for an input.
Multi-element messages can accept up to ten pages of free text or up to 16 lines (4 pages) of input
in a single message.
The following sample messaging sequences demonstrate typical uplink and downlink elements in
common transaction dialogs:
•
• DM (Downlink Message) with Unit Assignment, Selection List, Verify Message Construction
• DM (Downlink Message) Intuitive Units (Speed Request), Message Log
• UM (Uplink Message) Instructions That Require Aircrew Response
3.4.1 DM (Downlink Message) with Unit Assignment, Selection List, Verify
Message Construction
This example represents a solicited (aircrew initiated) transaction that demonstrates: