A UNITED STATES PART 121 CARRIER IS ACCUSED OF NON ADHERENCE TO OCEANIC CLRNC; A SPD DEV; BY SHANWICK CTL.

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AT FL310 CRUISE MACH .80 WE WERE CALLED ON SELCAL BY SHANWICK OCEANIC TO CONFIRM OUR MACH WAS .80. WE CONFIRMED .80 MACH AS PER OUR CLRNC. WE STRICTLY ADHERED TO MACH .80 DURING THE ENTIRE FLT AS PER OUR CLRNC. WE WERE THEN CALLED A FEW MINS LATER AND CLRED TO CRUISE AT FL330. WE RPTED VACATING FL310 AND REACHING FL330 MAINTAINING .80 MACH THROUGHOUT. SHORTLY AFTER PASSING AT 58 DEGS N LONGITUDE; 30 DEGS W; WE WERE CALLED AGAIN BY SHANWICK OCEANIC AND ADVISED SOME SORT OF DEV RPT WOULD BE FILED DUE TO OUR SEPARATION SUPPOSEDLY CHANGING FROM 10 MINS TO 8 MINS; THEN TO 7 MINS. WE WERE NEVER MORE THAN 1 MIN EARLY AT ANY RPTING POINT. OUR TCASII ONLY SHOWED TFC IN FRONT OF US AT FL350 AND FL370. I BELIEVE; SINCE WE STRICTLY ADHERED TO OUR CLRNC; AND OUR COMPANY FLT AHEAD OF US AT FL350 KEPT ABOUT THE SAME POS ON OUR TCASII DISPLAY; THERE MUST HAVE BEEN SOME PROB WITH SHANWICK OCEANIC WITH REGARD TO THEIR RESPONSIBILITY TO ASSURE ADEQUATE LONGITUDINAL SEPARATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR; THE CAPT; WAS UNABLE TO SHED MUCH LIGHT ON THIS INCIDENT AS HE HAS NOT HEARD ANYTHING FROM ATC OR FAA. HE HAD DISCUSSED THIS EVENT WITH HIS DISPATCH OFFICE. THEY FELT THAT IT MIGHT HAVE INVOLVED A MIL ACFT AHEAD OF THEIR ACFT AND FOR SOME UNKNOWN REASON; SHANWICK HAD SINGLED OUT THE ACR FLT AS THE CULPRIT. THE TCASII RANGE IS LIMITED AND ANY ACFT FARTHER AWAY THAN 7 MINS OR ABOUT 54 MI; WOULD NOT BE SEEN. THE TCASII RANGE IS ABOUT 40-50 NM. ACFT POS RPTS FROM THE MIL ACFT MAY ALSO HAVE BEEN ON A DIFFERENT FREQ RANGE OR ASSIGNMENT.