A FALCON 2000 CAPT RPTED THAT THERE MAY HAVE BEEN A MISUNDERSTANDING REGARDING REQUESTED AIRSPD WHEN IN EISN AIRSPACE.

Narrative

I WAS PIC INITIALLY FLYING R SEAT. DEPARTING SHANNON; IRELAND; WE WERE INITIALLY CLRED FL390 BUT REQUESTED AND WERE CLRED TO FL430 PRIOR TO ENTRY POINT FOR XING. WE HAD 4 PLTS ON BOARD AND; PRIOR TO LEVELOFF; I HAD TO GO TO LAVATORY DUE TO UPSET STOMACH. AT LEVELOFF; WE WERE INITIALLY MAINTAINING MACH. AT ONE OF THE LATER XING FIXES WE WERE ONLY ABLE TO MAINTAIN .76. IT IS MY UNDERSTANDING THAT ONE OF THE OTHER PLTS NOTIFIED SHANNON IN A POS RPT THAT WE WERE MAINTAINING MACH .76. PRIOR TO REACHING THE EXIT POINT; GANDER RADIO CALLED AND WANTED TO KNOW MACH NUMBER. OUR MACH HAD DECREASED TO .74 AND IT WAS RPTED. THE TEMP WAS STANDARD +14 DEGS C. IN LESS THAN 50 MI; THE TEMP DROPPED TO STANDARD +10 DEGS AND THEN TO STANDARD +8 DEGS. WE REQUESTED MACH .78 AND THEN MACH .80 WITH THE CHANGE IN TEMP AND WE WERE ABLE TO MAINTAIN ASSIGNED SPDS. AGAIN; I AM NOT CERTAIN IF THE ORIGINAL CHANGE IN SPD WAS JUST RPTED IN A POS RPT OR A REQUEST WAS MADE AND A NEW MACH GIVEN. WE WERE FLYING AT OUR MAX TEMP AND WOULD HAVE BEEN UNABLE TO MAINTAIN A HIGHER MACH NUMBER.