THE FLC OF A B747-200 FREIGHTER DSNDED BELOW ASSIGNED ALT WHILE ON AN APCH CTLR'S VECTOR CLRNC. THE APCH CTLR MISTAKENLY GAVE THE WRONG ALTIMETER SETTING AND THE FLC DSNDED TO THE ASSIGNED ALT WHICH CORRESPONDED TO THAT ALTIMETER. ALTDEV EXCURSION FROM ASSIGNED.

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WE HAD RECEIVED THE ATIS FOR DFW WHICH STATED THAT THE ALTIMETER SETTING WAS 29.39 WHICH WAS SET AT 18000 FT IN THE DSCNT. WE WERE CLRED TO 10000 FT. JUST AS WE LEVELED OFF AT 10000 FT; THE CTLR CAME ON TO SAY; 'CHK YOUR ALT AT 10000 FT; THE DALLAS ALTIMETER IS 30.39.' WE THOUGHT THAT THIS WAS A LITTLE STRANGE BUT RESET OUR ALTIMETERS AFTER READING BACK 30.39. NOW WE SHOWED 11000 FT SO WE CONTINUED DOWN TO 10000 FT. WHEN WE ARRIVED AT 10000 FT THE CTLR CAME BACK AND SAID THAT; 'I SHOW YOU AT 9000 FT; BUT THAT'S OK MAINTAIN 9000 FT.' WE THEN QUIZZED HIM ON THE ALTIMETER SETTING AGAIN AND HOW HE STATED 29.39. SOME FURTHER SMALL DISCUSSION TOOK PLACE BUT HE DIDN'T SEEM TO INDICATE THAT THERE WAS ANY CONFLICT. I AM NOT SURE WHAT HAPPENED; WHETHER HE JUST CAME ON AND DIDN'T HAVE HIS CONSOLE SET PROPERLY. WE SHOULD HAVE QUESTIONED HIM MORE AT THE START; BUT HE WAS SO ALARMED IN HIS STATEMENT (ACR CALL SIGN XXX; CHK YOUR ALT DFW ALTIMETER IS 30.39); WE THOUGHT THAT A CONFLICT WAS NEAR AND WE SHOULD ACT NOW! OUR CALL SIGN WAS USED FOR ANOTHER AIRLINE'S CARGO FLT; OPERATED BY OUR COMPANY IN A B747-200 FREIGHTER. IN THE FUTURE DON'T ASSUME THAT THE CTLR IS RIGHT AND THAT YOU MUST HAVE MESSED UP!