BE20 FLC DSND FROM ZAU ASSIGNED ALT ENRTE TO LAF CONCERNED ABOUT POS FROM ARPT; TFC AND APCHING TSTM.

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ON ARR TO LAF. CTR HERE HAS RADAR COVERAGE TO ONLY 4000 FT; SO THEY PERPETUALLY KEEP YOU HIGH. TWR HAS NO RADAR (HENCE; DAILY OCCURRENCES OF NMAC AND TFC CONFLICTS IN A HIGH DENSITY TRAINING ENVIRONMENT). WE WERE 10 NM FROM THE ARPT (LAF) AT 6000 FT AND THEN CLRED FOR VISUAL WHEN WE CALLED THE FIELD. WE HAD REPEATEDLY REQUESTED LOWER AND DID NOT CANCEL IFR FLT PLAN BECAUSE THERE WAS A TSTM S OF THE FIELD AND VERY HAZY DAY. MY COPLT WORKED THE RADIOS AND WE WERE CLRED TO 3000 FT WITH TFC ISSUED. CLRED FOR VISUAL WITH RECOMMENDATION TO MAINTAIN 3000 FT TILL WE HAD THE TFC. WE CALLED TFC IN SIGHT. I THOUGHT WE WERE HANDED TO TWR. WE EASILY MAINTAINED SEPARATION FROM THE TFC AND LANDED UNEVENTFULLY. ON TAXI IN; GND SAID WE UPSET CTR BY SWITCHING TO TWR EARLY WHILE THEY (CTR) WERE TRYING TO ALERT US TO TFC. I CALLED CTR SUPVR AT KANKAKEE. SHE SAID THE CTLR WAS JUST WORRIED ABOUT US AND THERE WAS NO PROB. MANY THINGS HERE: 1) NON RADAR ENVIRONMENT AT BUSY ARPT WITH MULTIPLE TYPES OF ACFT OPS; 2) CTR'S POLICY OF KEEPING ACFT HIGH; 3) FREQ CONGESTION; AND 4) WX -- THE TSTM HIT THE FIELD AS WE WERE HANGARING THE ACFT.