User's Guide

Table Of Contents
User Guide for the Envoy Data Link
Document Number: UG-15000 Rev. A Page 61 of 173
Emergency Contract
The ADS-C application also supports emergency alerting. An ADS-C emergency report is a
periodic report that is tagged as an “emergency” report, allowing the emergency situation to be
highlighted to ATC.
An ADS-C emergency can be triggered by the aircrew in a number of ways:
Manually, by selecting the ADS-C emergency function;
Indirectly, by triggering another type of emergency alerting system (e.g. transmission of a CPDLC
position report or selection of an SSR emergency code); and
Covertly (The availability of that functionality may vary between aircraft types).
Once an ADS-C emergency has been triggered, under normal circumstances the avionics will
continue to transmit ADS-C emergency periodic reports until the aircrew de-selects the ADS-C
emergency function.
Event Contract
An event contract allows an ATSU to request an ADS-C report whenever a specific event occurs.
An ATSU can establish only one event contract with an aircraft at any one time. However, the
event contract can contain multiple event types, including:
Waypoint change event (WCE)
Level range deviation event (LRDE)
Lateral deviation event (LDE)
Vertical rate change event (VRE)
An event contract remains in effect until the ATSU cancels it or until the event(s) used to trigger the
report occurs. The waypoint change event contract triggers a report for all waypoint changes. All
other event contracts will trigger a report on the first occurrence only and then the ATSU needs to
request a new event contract.
Groups
The aircraft system sends specific aircraft data in different groups of an ADS-C report. Each group
contains different types of data. An ADS-C event report contains only some of the groups, which
are fixed. The ADS-C periodic report can contain any of the ADS-C groups, which the ATSU
specifies in the contract request. The ADS-C report groups consist of:
Basic group
Flight identification group
Earth reference group
Air reference group
Airframe identification group
Meteorological group
Predicted route group
Table 4-1 provides examples for each ADS contract type: