Date: 201508
Local time of day: 0001-0600
Location: CZQX.ARTCC, NF
Light: Night
Aircraft: B747 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center CZQX
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: ATC Issue All Types
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: ATC Equipment / Nav Facility / Buildings
Primary problem: ATC Equipment / Nav Facility / Buildings

Narrative: En route we requested Our Oceanic clearance with Gander about :55 mins prior to entering oceanic at WPT Joopy; We requested FL350 Mach .86 (on NAT Z); About :30 mins prior to entering oceanic at WPT Joppy we received via ACARS our Oceanic clearing us to enter and cross on NAT Z just as requested; The clearance read maintain FL350; Sometime after entering oceanic (we passed WPT Joopy on our way to 050W) and CPDLC established with Gander we requested to climb to FL360 due to performance via CPDLC; to that ATC came back via CPDLC moments later responding 'unable due to traffic'; we then accepted that ATC CPDLC response from Gander and continue to maintain FL350; A few minutes later after we had been denied the climb to FL360 we then received a second oceanic crossing clearance via ACARS clearing us on the same Track and same Mach; but this time it read maintain FL360; We did not accept this clearance; we stayed at FL350 as FL350 was the original altitude and clearance that we had accepted and we immediately proceeded to contact Dispatch to briefly explain what just happened and to request a phone patch with Gander to clarify this second clearance (since I considered this was a bit long to explain over HF with gander radio) as I wanted to ask the reason for Gander sending us a second Oceanic saying to maintain FL360 after the fact that we had already entered oceanic and we had accepted a previous oceanic clearance at FL350 just as requested for the Oceanic entry at WPT Joopy on NAT Z and all this was after the fact that we had been told by Gander 'unable the climb to FL360 due to traffic' just minutes prior as this was a bit confusing to us. I started explaining what happened to Gander ATC via SATCOM (with Dispatch listening on the phone patch) The Gander ATC controller seemed confused and surprised as to why we had received a second oceanic clearance and said that the only thing they showed on their system was the first clearance that we've received and accepted; and he said to disregard that second clearance which ATC said they had no record of; and to continue to maintain FL350 just as we were since there was traffic at FL360; The ATC controller commented that 'some weird stuff had been happening lately with their ACARS system and that they were aware of it and that things like this were just dangerous' he also suggested for us to inform Gander radio of what happened which we proceeded to do briefly via HF. I explained to Gander that we just wanted for everyone to know that we were at FL350 and we just wanted to clarify the situation for everyone's sake.We continued the flight at FL350; (there was never any kind of altitude deviation at all); we never pressed the button to accept the second clearance that read FL360 to avoid any kind of confusions with Gander ATC among other reasons; but this meant ACARS was showing that second unaccepted clearance msg; and the acceptance prompt on the ACARS; plus an ACARS MSG was shown on the upper Eicas the whole way across until we parked and left the airplane to go to the hotel.1-Make flight crews aware that ACARS glitches do happen; and that Gander ATC has been having some issues with their ACARS system lately (as the Gander controller explained to us) 2-Remind crews the importance of always verifying all ATC ACARS clearance; and if there is any doubts ask ATC to clarify via any available means (E.I SATCOM; Phone patch)  3- Make sure before you accept a clearance of all its content and don't accept it until the crew is satisfy with that clearance.




Synopsis: B747 Captain reported receiving a second oceanic crossing clearance from CZQX via CPDLC after already accepting a first clearance and entering NAT Z. Gander indicated there had been ACARS difficulties and they had no idea where the second clearance came from. The second clearance had a lower clearance number but the same route at a higher altitude.