Manuel CPDLC V3.0. - Service d'Information Aéronautique Enna

3.7 End of Service and CPDLC Connection Transfer
3.7.1 Purpose and procedure
Under normal conditions, the current ATSU (Algiers ACC) initiates the CPDLC connection
termination sequence by sending an END SERVICE uplink message. In response to an END
SERVICE message:
• The avionics will downlink a DISCONNECT message. The avionics will consider the aircraft to be
disconnected as soon as the DISCONNECT message is sent.
• The current connection will be terminated, activating the non-active connection. The subsequent
ATSU will now be able to exchange CPDLC messages with the aircraft.
The success of the CPDLC transfer is dependent upon the next ATSU establishing its own CPDLC
connection prior to the END SERVICE message being received by the aircraft. Failure of the next
ATSU to establish a CPDLC connection before the END SERVICE reaches the aircraft will leave
the aircraft without CPDLC connectivity.
There are two cases in which the avionics will terminate established CPDLC connections.
• Depending on the software load, when any uplink messages remain open when the aircraft receives
an End Service.
• When the END SERVICE element is part of a multi-element message where none of the elements
require a WILCO response.
In both cases an error message will be generated to both ATS systems.
If any downlink messages remain open when the aircraft receives an END SERVICE message, the
avionics will close the messages and terminate the CPDLC connection with the current ATSU. This
will not affect the CPDLC connection with the next ATSU.
ATSU 1 ATSU 2
Active Connection
END SERVICE
DISCONNECT
REQUEST
Inactive Connection
Active Connection
CPDLC transfer sequence of an aircraft between two ATSUs
Operation Manual of CPDLC V3.0 Algiers FIR 20