A B747-200 CAPT COMPLAINED THAT HE MADE AN ALTDEV WITH SDF BECAUSE OF SIMILAR SOUNDING CALL SIGNS.

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I WAS THE CAPT OF A B747 OPERATING TO SDF. WE WERE IN THE DSCNT APCHING 10000 FT AND WERE GIVEN A CLRNC TO DSND TO 6000 FT. PASSING THROUGH APPROX 7500 FT; THE CTLR GAVE US A CLRNC TO 6000 FT AGAIN (OR SO WE THOUGHT). I REPLIED THAT WE HAD BEEN PREVIOUSLY CLRED TO 6000 FT. THE CTLR REPLIED THAT THE FIRST CLRNC HAD BEEN FOR ANOTHER FLT; BUT THAT IT WAS NO PROB AND WE COULD CONTINUE DSCNT TO 6000 FT. BOTH THE FO AND I AGREED THAT WE HEARD OUR CALL SIGN IN THE FIRST XMISSION. MAYBE THE CTLR SAID OUR CALL SIGN AND WAS THINKING THE OTHER; OR MAYBE WE JUST HEARD WHAT WE WANTED TO HEAR. I DID READ BACK THE ORIGINAL CLRNC AND DID NOT RECEIVE ANY CORRECTION FROM THE CTLR. ANYWAY; IT DOES NOT REALLY MATTER WHO IS AT FAULT. THE PROB STEMS FROM THE COMPANY USING SIMILAR CALL SIGNS WHICH ALL CONVERGE AT SDF AT THE SAME TIME. WHILE THE CALL SIGNS THE COMPANY USES ARE FOR THEIR OWN PURPOSES; HAVING SO MANY SIMILAR CALL SIGNS IS NOT IN THE BEST INTEREST OF SAFETY; ESPECIALLY WHEN ARR TIMES ARE SO CLOSE. IT IS VERY EASY FOR A BUSY APCH CTLR; OR FLT CREW; TO GET CONFUSED. MY OCCURRENCE WAS NOT THE FIRST TIME THIS HAS HAPPENED. IN FACT; OUR PLT GROUP HAS IDENTED THIS ISSUE AS A SAFETY CONCERN AND HAS BEEN TRYING; FOR SEVERAL YRS; TO CONVINCE THE COMPANY TO MAKE CHANGES.