FLC OF A DEHAVILLAND DASH 8 MISTAKENLY TOOK THE CLRNC FOR ANOTHER ACFT OF A SIMILAR CALL SIGN AND DSNDED BELOW ASSIGNED.

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CHKED IN WITH APCH CTL AS ACR X. WAS TOLD TO DSND AND MAINTAIN 5000 FT; WHICH I EXPECTED TO GET AS WE WERE AT 10000 FT. STARTED OUR DSCNT AND AT ABOUT 7200 FT APCH TOLD US TO STOP OUR DSCNT AT 7000 FT. THAT'S FINE. BUT THEN HE ASKED WHAT WAS OUR ASSIGNED ALT. I TOLD HIM 5000 FT. HE SAID WE WERE GIVEN 8000 FT AND THE 5000 FT WAS FOR ANOTHER ACFT. AT THIS TIME HE TOLD US THAT THERE WAS ANOTHER ACFT WITH A SIMILAR CALL SIGN. THEIR CALL SIGN WAS ACR Y WHO WAS ALSO ON FREQ. WE WERE NOT AWARE OF ANOTHER ACFT WITH SUCH A CLOSE CALL SIGN. 3 OF US IN THE COCKPIT HEARD THE SAME THING. WE ONLY HEARD ACR X AND I READ BACK THE 5000 FT AS ACR X; MAINTAIN 5000 FT. HE ALSO WARNED ACR Y OF THE SIT AS THEY HAD ANSWERED FOR US ALSO. WE BOTH BECAME AWARE OF THIS AND WERE AWARE OF IT AS WE SWITCHED THROUGH 3 MORE FREQS UNTIL WE LANDED. OUR ACTUAL FLT NUMBER WAS ACR X; BUT ON THIS FLT FOR ATC WAS CUT TO JUST ACR X. THE JETS USE THE 4 LETTERS AND WE IN THE DASH USE JUST 3 LETTERS. GETS A LITTLE CONFUSING AND WE MUST STAY ALERT. BUT WE ALSO NEED TO KNOW IF SIMILAR CALL SIGNS ARE OUT THERE AS SOME XMISSIONS GET CLIPPED AT THE VERY START IT SEEMS.