Narrative:

Cruising wbound at FL340; we had just passed latitude/long 1 at XA45Z; en route to latitude/long 2 (over the north atlantic) we had been requesting clearance for a higher cruising altitude for sometime. As we passed latitude/long 1; 2 opposite direction aircraft passed overhead and about 1 mi south of us. (At FL350; and I believe; FL370) at XB50Z a cpdlc message (controller pilot data lnk) came in from ZZZ oceanic to climb to and report reaching FL370. We accepted this clearance; climbed to FL370; and at XB53Z an automatic report was sent via cpdlc confirming that we were level at FL370. At XC07Z cpdlc message came in and it said; 'confirm climb clearance received said at time XC00 climb.' looking back at the original clearance message; we realized that it said; 'maintain FL340; at XC00Z climb to and maintain FL370; report level FL370.' we saw the climb clearance that we were anticipating; but missed the time to begin the climb. At this same time; XC07Z; we were conducting a crew change when a message came in to call ATC; which I did upon reaching the gate. Observations: 1) we saw the clearance that we were expecting and missed the conditional statement. 2) it might be safer to only issue a clearance when it can be executed ie; not at a conditional time. 3) fatigue may have contributed to our missing the conditional statement. I was unable to sleep on my previous rest break.

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Original NASA ASRS Text

Title: AN OCEANIC ACR CREW REPORTS A CPDLC CLB CLRNC WITH A SPECIFIC TIME TO START THE CLB. THE CREW CLBED EARLY BECAUSE THEY SAW THE CLRNC BUT MISSED THE TIME CONSTRAINT.

Narrative: CRUISING WBOUND AT FL340; WE HAD JUST PASSED LAT/LONG 1 AT XA45Z; ENRTE TO LAT/LONG 2 (OVER THE N ATLANTIC) WE HAD BEEN REQUESTING CLRNC FOR A HIGHER CRUISING ALT FOR SOMETIME. AS WE PASSED LAT/LONG 1; 2 OPPOSITE DIRECTION ACFT PASSED OVERHEAD AND ABOUT 1 MI S OF US. (AT FL350; AND I BELIEVE; FL370) AT XB50Z A CPDLC MESSAGE (CTLR PLT DATA LNK) CAME IN FROM ZZZ OCEANIC TO CLB TO AND RPT REACHING FL370. WE ACCEPTED THIS CLRNC; CLBED TO FL370; AND AT XB53Z AN AUTO RPT WAS SENT VIA CPDLC CONFIRMING THAT WE WERE LEVEL AT FL370. AT XC07Z CPDLC MESSAGE CAME IN AND IT SAID; 'CONFIRM CLB CLRNC RECEIVED SAID AT TIME XC00 CLB.' LOOKING BACK AT THE ORIGINAL CLRNC MESSAGE; WE REALIZED THAT IT SAID; 'MAINTAIN FL340; AT XC00Z CLB TO AND MAINTAIN FL370; RPT LEVEL FL370.' WE SAW THE CLB CLRNC THAT WE WERE ANTICIPATING; BUT MISSED THE TIME TO BEGIN THE CLB. AT THIS SAME TIME; XC07Z; WE WERE CONDUCTING A CREW CHANGE WHEN A MESSAGE CAME IN TO CALL ATC; WHICH I DID UPON REACHING THE GATE. OBSERVATIONS: 1) WE SAW THE CLRNC THAT WE WERE EXPECTING AND MISSED THE CONDITIONAL STATEMENT. 2) IT MIGHT BE SAFER TO ONLY ISSUE A CLRNC WHEN IT CAN BE EXECUTED IE; NOT AT A CONDITIONAL TIME. 3) FATIGUE MAY HAVE CONTRIBUTED TO OUR MISSING THE CONDITIONAL STATEMENT. I WAS UNABLE TO SLEEP ON MY PREVIOUS REST BREAK.

Data retrieved from NASA's ASRS site as of May 2009 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.