B777 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 200; Flight Crew Total 13241; Flight Crew Type 1728
Human-Machine Interface
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Procedure
Upon receipt of initial oceanic clearance; I reviewed the message along with the captain and accepted via CPDLC with CZQX; it was rejected almost immediately and then a 2nd message arrived within about 5 seconds that appeared the same as the first; so it was re-accepted. It seemed as though it was a system anomaly but in fact had a change from FL380 to FL390 for crossing. No ATC verbal 'amendment to clearance' was given as is usually the case. About this time we did crew change. I was told after break that the FL390 was noticed by Gander domestic prior to track entry and we entered track correctly so the system checks worked fine.
Requested oceanic clearance. Upon receipt of clearance the FO and I reviewed same and confirmed the track/alt with what we were filed and requested and confirmed it was the same. Accepted via CPDLC with CZQX. It was rejected and almost instantly and within seconds a new clearance arrived with same track. We accepted. We did not realize we had accepted 2 clearances with the second having 390 not 380 as crossing altitude. This all happened in a total of 20 seconds or so. Did pilot change did crew briefing advising new PM that we have oceanic. We were at 370 and had requested climb to track altitude. When new PM was in seat i said request a climb to 380. We climbed to 380. A short time later gander domestic cleared us to climb to 390. We questioned him as we thought our alt should be 380. He said I'll verify. He came back and said at this time you now cleared to cross at 390 which we did. Gander domestic did not say be advised you have an amended clearance as he did to flights that had one that evening. We entered track on course and at cleared altitude.
B777 flight crew reported receiving two oceanic clearances within five seconds from Gander and accepted both. A flight level change was assigned with the second clearance which the crew did not detect.  Reportedly; their HF radio could transmit; but not receive.