FLC OF A L1011; STOPPED CLB AT FL270 AND DONNED OXYGEN MASKS DUE TO A PRESSURIZATION PROB. ATC WAS NOTIFIED AND A NEW XPONDER CODE GIVEN TO MAKE AN EMER DSCNT. HOWEVER; THE SO OVERCAME THE PROB AND THE FLT CONTINUED AS NORMAL.

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DURING CLBOUT FROM MANCHESTER; ENGLAND; THE CABIN ALT WARNING HORN SOUNDED AS WE PASSED THROUGH FL270. I REMOVED MY BOOM MIKE/HEADSET WHILE DONNING MY OXYGEN MASK AND DID NOT HEAR A XMISSION THAT THE FO MADE TO LONDON CTL. WHEN I GOT BACK INTO THE COM LOOP; I HEARD LONDON ASKING WHAT THE NATURE OF OUR EMER WAS. I RESPONDED THAT WE WERE HAVING A PROB WITH THE PRESSURIZATION. THE CTLR THEN TOLD US TO SQUAWK 7700; WHICH I DID; AND CLRED US TO DSND TO FL240. BY THIS TIME THE SO HAD RESOLVED THE PROB AND I TOLD LONDON THAT WE DID NOT WANT TO DSND AND WOULD LIKE TO MAINTAIN OUR PRESENT ALT TO ENSURE THAT WE HAD IN FACT RESOLVED THE PROB. SHORTLY THEREAFTER I INFORMED LONDON CTL THAT WE DID HAVE EVERYTHING BACK TO NORMAL AND HE ASKED WHAT OUR INTENTIONS WERE. I TOLD HIM WE WANTED TO RESUME THE CLB TO FL310 AND REQUESTED CLRNC DIRECT TO 55N 10W; OUR OCEANIC ENTRY FIX. HE CLRED US AS REQUESTED AND SWITCHED US TO SCOTTISH CTL. SCOTTISH ASKED IF THE PAX OXYGEN MASKS HAD BEEN DEPLOYED AND I TOLD HIM THAT WE MANAGED TO AVOID THAT. I THEN ASKED SCOTTISH FOR A NEW XPONDER CODE WHICH HE SUPPLIED. AFTER EVERYTHING SETTLED; AND WE HAD THE FMS REPROGRAMMED WITH THE REVISED OCEANIC CLRNC WE RECEIVED JUST PRIOR TO THE PRESSURIZATION PROB; I BEGAN WONDERING WHAT HAD CAUSED LONDON CTL TO THINK WE WERE DECLARING AN EMER AND WANTED TO DSND. I ASKED THE FO WHAT HE HAD SAID TO LONDON WHILE I HAD MY HEADSET OFF. HE REPLIED THAT HE HAD INFORMED THEM THAT WE WERE HAVING PRESSURIZATION PROBS AND WE WOULD GET BACK TO HIM. I ASKED HIM IF HE HAD DECLARED AN EMER AND HE REPLIED THAT HE HAD NOT.