CL65 FLT CREW LNDG AT SPI FAILS TO CONTACT TWR FOR CLRNC BUT OBSERVES LIGHT GUN SIGNAL CLRNC FROM TWR.

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WHILE OPERATING FROM ORD TO SPI; WE WERE KEPT AT 11000 FT BY ZAU AND HANDED OFF TO SPI APCH APPROX 20 NM FROM SPI. THE SPI CTLR CLRED US TO 2200 FT; GAVE US A NEW SQUAWK AND TOLD US TO EXPECT RWY 22 VISUAL APCH. BY NOW; WE WERE WITHIN 18 NM OF THE ARPT AND TRYING TO LOSE ABOUT 11000 FT OF ALT. THE FO WAS THE PF AND CALLED THE ARPT IN SIGHT. I ALSO HAD THE ARPT AND TOLD THE CTLR THAT THE ARPT WAS IN SIGHT; AT WHICH POINT SHE CLRED US FOR THE VISUAL APCH RWY 22. BY NOW WE HAD TO RUN 2 CHKLISTS AND CONFIGURE THE AIRPLANE FOR LNDG AND STABILIZE THE RATE OF DSCNT. THE FO STABILIZED THE ACFT AT 700 FT AGL ON SHORT FINAL. THE SPI CTLR NEVER HANDED US OFF TO THE TWR CTLR AND AS WE WERE RUSHED THROUGHOUT THE APCH; WE FINISHED ALL REQUIRED CHKLISTS. AS WE WERE ABOUT 100 FT AGL; I NOTICED A GREEN LIGHT SIGNAL FROM THE TWR WHICH DID NOT SET OFF ANY FLAGS; BUT INDEED IT WAS A LNDG CLRNC LIGHT SIGNAL FROM THE TWR. WE HAD NOT SWITCHED TO TWR AND DID NOT ESTABLISH VOICE COM BEFORE LNDG. ONCE ON THE GND; I CONTACTED THE CTLR AND HE ASSURED ME THAT THERE WAS NO PROB ON THE ATC'S PART AND THAT HE IN FACT HAD CLRED US TO LAND USING A LIGHT SIGNAL. THIS SIT WAS INDUCED BY ZAU'S TENDENCY TO KEEP ACFT THAT HIGH WHILE FLYING TO SPI AND THE SPI APCH CTLR'S FAILURE TO HAND US OFF TO THE TWR CTLR. THE ABOVE MENTIONED FACTORS TOGETHER WITH THE INCREDIBLE WORKLOAD IN THE COCKPIT CREATED A CHAIN OF EVENTS THAT CAUSED US TO ALMOST LWOC. IT WAS SOLELY THE SPI TWR CTLR'S VIGILANCE AND SITUATIONAL AWARENESS THAT MADE THIS SIT SAFE. I BELIEVE THAT THERE HAS TO BE MORE PLANNING ON ZAU'S PART TO GIVE TURBOJETS FURTHER DSCNT CLRNC FARTHER FROM THE SPI ARPT TO PREVENT SUCH INCIDENTS AND CHAIN OF EVENTS FROM BUILDING UP.