Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 35; Flight Crew Total 5000; Flight Crew Type 700
Communication Breakdown
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Procedure; Human Factors
After taking the first rest period; I relieved the Captain who was the pilot flying. The FO (First Officer) informed me that we had received a clearance to climb at the next fix and showed me the printout of the clearance. It read 'FM ELSIR/1136 MNTN FL350'. We talked about this and determined that it was a CPDLC (Controller Pilot Datalink Communications) clearance to climb to depart ELSIR at FL350 and .84 mach. We commenced a climb roughly two minutes prior to ELSIR to depart that fix at FL350 and .84. A few minutes after completing the climb; Gander called us and said that what we received was not a clearance to climb. The controller said; 'just so you know for next time; you need to call me before climbing.' He added; 'I know that clearance we sent you was poorly worded'. After copious apologies from us; he again stated that there was no problem or conflict; just wanted to make sure we knew.Lesson learned that we get used to climbing after getting messages; so it didn't feel strange to be doing so. This was certainly a mistake on my part; but as we move into this era of more CPDLC messaging I can see this problem recurring in the future with other crews. We were lucky there was no conflict in this incident. Maybe this is an issue that we could discuss in recurrent?
We received oceanic clearance from Gander via CPDLC (Controller Pilot Datalink Communications). Our clearance included routing and instructions to climb from FL330 to FL350 at 1136Z prior to the coast-out point ELSIR. We commenced climb from FL330 to FL350. Gander Domestic queried our climb and apologized for the 'poorly written' altitude clearance; but advised that we should have requested the climb via VHF voice prior to commencing. We acknowledged and continued our climb to FL350 with no traffic conflict.
Air carrier flight crew reported climbing from the assigned altitude after receiving an clearance via CPDLC; then being advised of a misunderstanding of the clearance.