SIMILAR CALL SIGN PROB ON N CANADIAN ROUTES BY PLT WHO FLIES 2 DIFFERENT AIRLINE CALL SIGNS.

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I WAS FO ON ACR X231 FROM ANC TO ORD. EDMONTON CTR CLRED US TO FL370. OUR POS WAS APPROX NCA13 BTWN DENTU AND THE PAS (YQD). WE WERE SWITCHED OVER TO WINNIPEG CTR. EDMONTON AND WINNIPEG WERE ALSO CTLING ACR Y321. FROM OCTOBER 1999 AND MARCH 2000; I FLEW ACR Y CALL SIGNS EXCLUSIVELY; INCLUDING 321. I ONLY FLEW ACR X CALL SIGNS DURING THE MONTH OF APRIL. WHEN CHKING IN WITH WINNIPEG; I BELIEVE I USED ACR Y321 CALL SIGN AND RPTED FL370. WINNIPEG RESPONDED 'YOU ARE NOT CLRED TO FL370; YOU ARE CLRED TO FL350.' I RESPONDED THAT EDMONTON HAD CLRED US TO FL370 AND THAT WAS OUR ASSIGNED ALT. WE MAY HAVE HAD AT LEAST 3-4 COMS TRYING TO ELIMINATE ANY CONFUSION. I FINALLY AGREED TO DSND TO FL350. I FELT UNCOMFORTABLE AND CHKED TCASII FOR ANY CONFLICT WITH OTHER TFC BEFORE COMMENCING DSCNT. ACR Y321 WAS GIVEN A FREQ CHANGE; THE SAME FREQ AS ACR X231. STILL FEELING UNCOMFORTABLE I CHKED BACK WITH WINNIPEG AND RPTED LEAVING FL355 FOR FL350. WINNIPEG SAID 'ACR X231 PLEASE STAND BY.' WINNIPEG STATED HE SPOKE WITH OTHER CTLRS AND WE WERE RESPONDING TO THE INCORRECT FLT NUMBER. I IMMEDIATELY RESPONDED THAT MAY HAVE BEEN THE CASE BECAUSE I FLY BOTH ACR X231 AND ACR Y321 FLT NUMBERS. WE STOPPED OUR DSCNT AT THAT POINT AND WERE CLRED TO CLB BACK TO FL370. I APOLOGIZED FOR THE CONFUSION AND WAS TOLD 'THAT'S OK.' CONSIDERATIONS FOR THE FUTURE. CHANGE FLT NUMBERS SO THEY ARE NOT SIMILAR ALONG THE SAME ROUTES. WINNIPEG'S COM WAS LESS THAN 5 BY 5.