CAPT OF ACR WDB ACFT MISUNDERSTOOD CLRNC AND REMAINED AT ALT INSTEAD OF CLBING TO NEWLY ASSIGNED ALT DURING HIGH ALT OCEANIC CRUISE.

Narrative

FLT WAS ENRTE FROM JFK TO OSA. THE FLT REQUIRED AN AUGMENTED CREW AND FO AND I RELIEVED CAPT AND FO. SHORTLY AFTER PASSING NOME. WE WERE BRIEFED REGARDING THE FLT STATUS AND PROCEEDED TO VERIFY POS AND PROGRAMMING OF OUR RTE. COMMONLY ON THIS RTE; CTR REQUIRES WHEN A FLT CAN CLB TO AN ALT COMPATIBLE WITH OCEANIC REQUIREMENTS AND COMMONLY ISSUES AN EXPECTED TIME OR LOCATION TO CLB. WE WERE UNSURE OF OUR ALT CLRNC; WHETHER WE WERE CLRED TO CLB TO FL370 OR CLRED TO EXPECT FL370. CTR COMS ARE NOT AVAILABLE IN THAT AREA AND COMRDO WAS DIFFICULT AT THAT TIME AND AT BEST; A SLOW RELAY FROM CTR. I REMAINED AT FL350 UNTIL REACHING ANC CTR; ABOUT 10 MINS PRIOR TO NEEVA. THEY ADVISED THAT WE HAD BEEN CLRED TO FL370. AT NEEVA INTXN; I RPTED FL350 IN ERROR AND CTR QUESTIONED THE ALT. I ACKNOWLEDGED THE ERROR IN RPTING; AND CONFIRMED THE CORRECT ALT; FL370. THERE APPARENTLY REMAINED A QUESTION IN CTR'S MIND AS TO OUR ALT BUT NO FURTHER INQUIRY WAS MADE AND ALT RPTING MUST HAVE CONFIRMED OUR ALT. A FORM 8020-17 WAS INITIATED BY CTR AND AN OCCURRENCE RPT SUBMITTED TO COMPANY.