Date: 201703
Local time of day: 1201-1800
Location: CZQX.ARTCC, NF
Flight conditions: VMC
Light: Daylight
Aircraft: Widebody Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
ATC / advisory: Center CZQX
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Workload; Troubleshooting; Situational Awareness; Distraction; Confusion
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Environment - Non Weather Related; Procedure; Aircraft
Primary problem: Procedure

Narrative: About 45 minutes after getting airborne we logged into Moncton via CPDLC; and were accepted. Prior to entry into Moncton; CPDLC went active and we proceeded with several frequency change request via CPDLC. We received our Oceanic Clearance via ACARS; and commenced our initial cross checks for coast out. At XA:17 we were advised by Moncton via VHF to switch frequencies from Moncton to Gander Radio. The controller informed us that there had been or are issues with the message he sent to us that he had requested via ADS/CPDLC to switch frequencies. He told us we may get a delayed message from them and to disregard. We thanked him and noted his comment. We switched to Gander; and we were cleared direct to our second oceanic fix N51W050; having already been cleared direct to ALLRY by a previous controller which was our initial entry point. We checked in and received our HF frequencies and received a SELCAL check and confirmed proper operation; and advised we were CPDLC. We coasted out with no abnormal indications; all systems appeared to be operating nominally. We monitored 123.45 and 121.50 and were now squawking 2000 on the transponder. We crossed N51W050 at XB:46Z About two hours after our initial Gander contact we received an ATC message '/CONTACT GANDER CENTER ON 133.90' Having already coasted out; and in CPDLC/HF contact and remembering the previous controller having informed us that an erroneous message may be forthcoming; sent a message response as 'Unable' so it was not in an affirmative response to the system. That way if there was an actual need to contact us; It would be thru non VHF sources since we were beyond VHF range at this point. Ten minutes later we got a flurry of messages (3) '/MESSAGE NOT SUPPORTED BY THIS AT FACILITY' At this time I suspected that the CPDLC buffer may be 'jammed' or locked up. I told the PF that we need to do a 'Control-ALT-Delete' to the CPDLC because I suspected that based on the types of messages ATC is not sending them and anything we are attempting to send is getting bounced by the system. Around this exact time; on VHF 121.5 another aircraft called us and told us to contact Gander on HF 8864; they were trying to reach us. Apparently Gander had sent a SELCAL; but it was not received by the plane. When we tried reaching Gander on 8864; we were unable and transmission was at best 1/5. We switched to our secondary on 11279 and established good contact with them and they informed us that they did not receive our N51W050 position report via CPDLC. I informed them that we had just noticed that our CPDLC may need to be logged off and then back on. I relayed at this time our N51W050 position report. I had the FO log off the CPDLC and re-login; ATC communication was immediately accepted. I asked ATC via HF to confirm CPDLC contact and that we had just sent a position report to them via CPDLC. Eighteen minutes later we received a CPDLC/ATC message confirming contact via CPDLC. One minute later we responded to the customary route confirmation message. All operations with CPDLC were normal from this point forward and flight was uneventful. A Couple things come to mind in all this. First; we fell for a false expectation of accepting a communication failure with Moncton as 'Normal'. There is a lack of affirmative information to the crew that CPDLC is operating; in our case it was the multiple failure messages that gave us the indication of a CPDLC failure which we immediately acted on to rectify. I was somewhat surprised at how rapidly 8864 HF had grown weak; normally Gander has very good reception out in this area; thankfully the procedure of a secondary worked and we regained contact. Following procedures and having our Air to Air and Guard frequencies dialed in; worked as advertised! I'm open to what I can do differently next time to identify a CPDLC buffer is sue like this and prevent a delayed or even missed position report.




Synopsis: Air carrier Captain on a North Atlantic track reported contacting Moncton then Gander via CPDLC. Later; ATC requested the crew check in via HF because CPDLC was not reporting its position. A CPDLC reset reestablished contact.