CPR LTT ON APCH MIS-HEARS CLRNC; ALTDEV.

Narrative

DURING THE APCH PHASE TO AN ILS APCH AT BUR; APCH CTL CLRED US TO DSND AND MAINTAIN 4000 FROM OUR PREVIOUSLY CLRED 7000. AFTER ACKNOWLEDGING AND RESETTING THE ALT ALERTER; I ADVISED THE CAPT I WAS CONTACTING THE FBO ON OUR OTHER COM RADIO. I LISTENED TO THE CAPT RECEIVE A FREQ CHANGE AND AFTER FINISHING MY CONTACT WITH THE FBO I LISTENED WHILE THE CAP ATTEMPTED TO CONTACT THE NEXT CTLR WHILE WE CONTINUED OUR DSCNT. DUE TO THE CTLR HANDLING 2 OR 3 VFR REQUESTS AND 1 OTHER IFR ACFT THE CAPT WAS UNABLE TO CHK IN AFTER 4 TRIES. THE CAPT LEVELED AT 4000 AND I CHKED IN 'LEVEL 4000.' THE CTLR IMMEDIATELY RESPONDED WITH 'YOU WERE CLRED TO 5000; TURN R IMMEDIATELY HDG 160 DEGS.' THE CAPT INITIATED THE R TURN AND XMITTED THAT WE WERE CLRED TO 4000 FT. THE CTLR REPLIED; 'TFC 10 TO 11 O'CLOCK AND 4 MI.' WE SAW THE SINGLE ENG AND CALLED TFC IN SIGHT AND WERE GIVEN A NEW HDG TO INTERCEPT THE FINAL APCH. DURING A PHONE CONVERSATION AFTER THE FLT THE SUPVR OF THE FACILITY TOLD THE CAPT THE TAPE HAD US CLRED TO 5000. THE CAPT AND I BOTH STILL BELIEVE WE WERE CLRED TO 4000. THERE WAS NO QUESTION; AT THE TIME; AS TO OUR ALT ASSIGNMENT. THE PROB; OTHER THAN COM; WHICH IS MOST FREQUENTLY THE PROB; WAS THE CTLR'S FEELING THAT THE VFR REQUESTS HAD A HIGHER PRIORITY THAN THE IFR ACFT IN THE APCH PHASE OF A FLT. OUR INABILITY TO CHK IN AND COMMUNICATE OUR INTENT TO DSND TO 4000 WAS CRITICAL IN THIS INCIDENT. A TURBOJET ACFT DSNDING AT 2-3000 FPM AND DOING 250 KTS SHOULD HAVE SOME PRIORITY OVER SMALLER VFR SINGLES DOING 100 KTS AND DSNDING OR CLBING AT 500 TO 1000 FPM.