Loss of CPDLC connection with momentary DATA LINK CPDLC FAIL CAS message
Effectivity: Global 7500
ATA: 23-22
By: Lahcene Bensalem - Technical Services Operators have reported occasional loss of Controller Pilot Data Link Communication (CPDLC) connection confirmed by a momentary “DATA LINK CPDLC FAIL” advisory CAS message. When it occurs, the CPDLC page goes blank with “CPDLC APPLICATION NOT AVAILABLE” displayed in the window.
The DLCA (Data Link Communication Application) page self-recovers after few seconds, the DATA LINK CPDLC FAIL advisory CAS is removed, and the CPDLC status label “CONNECTION TERMINATED” and LOGON status label “LOGON REQUIRED” are displayed on the CPDLC LOGON/STATUS page. This indicates that a logon is required before further CPDLC operations.
The flight crew must perform a manual logon to the current ATC (Air Traffic Controller) authority. The flight crew is expected to revert to voice to maintain communications with ATC until CPDLC service is reestablished.
Following investigation, it has been confirmed that the ATN (Aeronautical Telecommunication Network) CPDLC application drops the CPDLC connection following a DLCA software reset, due to incorrect handling of a specific message from the ground station.
The condition only occurs after a CPDLC Next Data Authority (NDA) is established and then a uM117 CONTACT [ICAOunitname][frequency] is sent simultaneously (concatenated) with a uM161 [end service] from the ground station during Current Data Authority (CDA) handoffs, when nearing FIR (Flight Information Region) boundaries.
In all events, no OMS active or historical fault is recorded. Under the condition described above, not having an OMS fault code associated with "DATA LINK CPDLC FAIL" is normal, given that the DLCA reset does not require maintenance action.
The condition is addressed in the next DLCA version which is part of future avionics upgrade V2.5.
In the interim, we are currently drafting a FON (Flight Operation Notification) AVNC-051-NC to provide flight crew guidance.