COMMUTER ACFT CLRED FOR PROC TURN; DSNDS TO PUBLISHED ALT. CTLR EXPECTS HIM TO REMAIN AT LAST ASSIGNED ALT.

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AIRLINE FLT ABC IN CONTACT WITH TYLER; TX; APCH CTL AT 3000 FT. CLRED 'TO TYLER LOM; RPT PROC TURN INBOUND; FOR ILS RWY 13.' ABC GOES DIRECT TO TYLER LOM; TURNS OUTBOUND 309 DEGS; STARTS TIMING; AND BEGINS DSCNT TO 2000 FT AS PUBLISHED. ON INBOUND TURN AND JOINING LOC; RPTS 'ABC; PROC TURN INBOUND.' APCH RESPONDS; 'ROGER; MAINTAIN 2500 FT UNTIL ESTABLISHED ON THE LOC; CLRED ILS RWY 13 AT TYLER.' SINCE ABC WAS ALREADY ON THE LOC AT 2000 FT AND OTHER ACFT WERE IN THE AREA; I CLBED TO 2500 FT THINKING IT WAS POSSIBLY A TFC AVOIDANCE SIT; RECAPTURED GS AND EXECUTED APCH. NORMAL LNDG; SLIGHTLY LONG. TYR APCH SHOULD ISSUE SPECIFIC ALTS IF THOSE REQUIRED ARE DIFFERENT FROM PUBLISHED. APCH AND PROC TURN WERE FLOWN AS PUBLISHED; WITH NO RESTR ISSUED. APCH'S 2500 FT ALT CALL GENERATED SIGNIFICANT CONFUSION IN COCKPIT. SUPPLEMENTAL INFO FROM ACN 318526: BETTER COM ON BOTH SIDES COULD HAVE CLRED THIS SIT UP. THE CTLR COULD HAVE BEEN MORE SPECIFIC ON THESE DIRECTIONS. I ALSO FOUND IT ODD THAT HE DIDN'T SEEM TO REALIZE THAT WHEN YOU RPT PROC TURN INBOUND; YOU ARE ESTABLISHED INBOUND ON THE LOC.