Narrative:

We were on a random track oceanic crossing of the atlantic. Cpdlc established with gander and HF contact with gander on HF radio. We received a cpdlc message from gander: 'gander ATC advises higher flight level may be available if requested.' we were at this time at FL300. We checked our flight planned altitudes and performance page and agreed that we could climb to FL340. We submitted cpdlc request for 'request climb to FL340 due to performance' two minutes later. Twelve minutes had passed and we did not get a response from gander. During this time we were starting to experience light to moderate turbulence so we initiated another cpdlc request to gander to 'request climb to FL340 due to weather.' seven minutes later we received an uplink from gander: 'climb to reach FL340 by N5456.0 W041; report level FL340.' we accepted this uplink and started our climb to FL340. When level; we sent the 'armed level at FL340' report via cpdlc. I should note that we were careful to check TCAS to ensure there were no other aircraft in the area that we may cross altitudes with. There was only one other flight behind us by 35 NM; no other traffic. About 5 minutes after level off at FL340; we received a SELCAL page and got on the HF to talk to gander. They told us that gander needed us at FL310. We did not question the instructions and began a descent to FL310 and reported level at FL310 to gander via voice on HF. A few minutes later; we received another SELCAL page from gander and they wanted us to re-confirm that we were at FL310. We confirmed this on HF voice and submitted a cpdlc plain text message stating that: 'we are still maintaining FL310.' we did not hear from gander again except via SELCAL page when they requested a voice position report. At this time we also submitted a cpdlc position report. Not sure why there was confusion about the altitude; but we do have copies of the cpdlc uplinks and downlinks that show we did get clearance to climb to FL340. ATC must have decided they had made a mistake to allow us to climb to FL340 and re-assigned us to FL310. We immediately complied with all ATC instructions and are not aware of any traffic conflicts that may have been caused. Unknown why ATC assigned us to FL340; then after we had leveled; decided they wanted us at FL310. Seemed that our cpdlc data link was slow to process and may have contributed to any confusion there may have been.

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Original NASA ASRS Text

Title: B777 flight crew reports confusing clearances from Gander Oceanic after receiving an offer for; and accepting FL340. Once level they are told to maintain FL310; and after verifying; the crew descends to FL310.

Narrative: We were on a random track oceanic crossing of the Atlantic. CPDLC established with Gander and HF contact with Gander on HF radio. We received a CPDLC message from Gander: 'Gander ATC advises higher flight level may be available if requested.' We were at this time at FL300. We checked our flight planned altitudes and performance page and agreed that we could climb to FL340. We submitted CPDLC request for 'Request Climb to FL340 due to performance' two minutes later. Twelve minutes had passed and we did not get a response from Gander. During this time we were starting to experience light to moderate turbulence so we initiated another CPDLC request to Gander to 'Request climb to FL340 due to weather.' Seven minutes later we received an uplink from Gander: 'Climb to reach FL340 by N5456.0 W041; report level FL340.' We accepted this uplink and started our climb to FL340. When level; we sent the 'armed level at FL340' report via CPDLC. I should note that we were careful to check TCAS to ensure there were no other aircraft in the area that we may cross altitudes with. There was only one other flight behind us by 35 NM; no other traffic. About 5 minutes after level off at FL340; we received a SELCAL page and got on the HF to talk to Gander. They told us that Gander needed us at FL310. We did not question the instructions and began a descent to FL310 and reported level at FL310 to Gander via voice on HF. A few minutes later; we received another SELCAL page from Gander and they wanted us to re-confirm that we were at FL310. We confirmed this on HF voice and submitted a CPDLC plain text message stating that: 'We are still maintaining FL310.' We did not hear from Gander again except via SELCAL page when they requested a voice position report. At this time we also submitted a CPDLC position report. Not sure why there was confusion about the altitude; but we do have copies of the CPDLC uplinks and downlinks that show we did get clearance to climb to FL340. ATC must have decided they had made a mistake to allow us to climb to FL340 and re-assigned us to FL310. We immediately complied with all ATC instructions and are not aware of any traffic conflicts that may have been caused. Unknown why ATC assigned us to FL340; then after we had leveled; decided they wanted us at FL310. Seemed that our CPDLC data link was slow to process and may have contributed to any confusion there may have been.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.