A C310 PLT EXPERIENCED AN NMAC WHILE IN THE PATTERN AT PWK.

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I FILED IFR FROM BIV TO PWK. WX WAS CAVU. PWK ATIS WAS RPTING ILS RWY 16 IN USE AND LNDG AND DEPARTING RWYS 30 AND 34 WITH ACFT UNABLE TO CIRCLE; TO ADVISE APCH CTL. WHEN INSIDE 20 MI E OF OBK (IAF FOR ILS RWY 16); I CANCELLED IFR AND WAS TOLD TO KEEP MY XPONDER CODE; DSND TO 2000 FT AND CONTACT PWK TWR. I CONTACTED PWK TWR AND WAS TOLD TO RPT R DOWNWIND FOR RWY 30 AND WAS GIVEN A NEW TXP CODE. WHILE I HEARD THE TWR TALKING TO OTHER ACFT; I WAS NOT AWARE OF ANY THAT WERE APCHING; LNDG ON RWY 30; NOR WAS I GIVEN ANY TA'S. (I BELIEVE THE TWR WAS HANDLING ALL COMS; BOTH AIR AND GND). WHEN ABOUT 2 MI FROM THE ARPT; I RPTED 'DOWNWIND FOR RWY 30;' I DID NOT GET ACKNOWLEDGEMENT AND THE TWR COMMUNICATED WITH ANOTHER ACFT. A FEW SECONDS LATER; I AGAIN ADVISED THE TWR OF MY POS AS I WAS CONCERNED ABOUT ENTERING O'HARE'S AIRSPACE. AGAIN; NO ACKNOWLEDGEMENT FROM THE TWR. I THEN SAW A BONANZA AT MY 2-3 O'CLOCK POS; XING FROM MY R TO L THAT I WAS IMMEDIATELY GOING TO PASS OVER THE TOP OF HIM AT ABOUT 100 FT! HAD I NOT BEEN A LITTLE HIGH ON MY APCH TO THE ARPT; THERE LIKELY WOULD HAVE BEEN A MESHING OF METAL. THE BONANZA CALLED THE TWR AND RPTED HIS POS AND ADVISED THEM THAT A TWIN HAD JUST PASSED RIGHT OVER THE TOP OF HIM. THE TWR CLRED THE BONANZA TO LAND ON RWY 30 AND DID NOT ACKNOWLEDGE THE RPT OF THE TWIN. I CALLED THE TWR AND AGAIN RPTED MY POS AND ADVISED THAT I HAD JUST PASSED OVER THE TOP OF A BEECH ACFT. THE TWR ADVISED THAT I WAS '#2 TO LAND ON RWY 30; AND THAT I MIGHT WANT TO CIRCLE FOR BETTER SPACING BEHIND THE BONANZA ON FINAL' WITH NO FURTHER ACKNOWLEDGEMENTS. I CIRCLED AND LANDED ON RWY 30 WITHOUT FURTHER INCIDENT. AS TO CORRECTIVE ACTIONS; OBVIOUSLY 'SEE AND AVOID' IS THE #1 -- ALTHOUGH IT IS AT TIMES EXTREMELY DIFFICULT TO SEE ACFT THAT ARE EVEN WITHIN LESS THAN A MI OF YOU. IN THINKING ABOUT THIS MATTER; I BELIEVE THAT AS I GOT CLOSE TO THE ARPT; I WAS COMPLACENT IN THINKING THAT THE TWR WOULD ADVISE ME OF OTHER TFC IN THE PATTERN. AT NO TIME DID I HEAR THE TWR ADVISE ANY OTHER ACFT OF TWIN TFC -- CERTAINLY; THEY DID NOT ADVISE THE BONANZA OF MY EXISTENCE; NOR DID I HEAR ANY REFERENCES TO RWY 30 FOR ANY OTHER ACFT. NONE OF THIS EXCUSES ANY RELAXATION OF EFFORT TO LOOK FOR OTHER ACFT. CERTAINLY; HAD THE TWR CALLED OUT TFC TO EITHER ACFT OR AT LEAST ADVISED EITHER OF US THAT THERE WAS ANOTHER ACFT HEADING TO THE SAME AREA; IT WOULD HAVE INCREASED THE SCANNING ACTIVITY IN 1 OR BOTH ACFT. OF MY MANY LNDGS AT PWK; THIS WAS THE FIRST TIME THAT I HAD CANCELLED IFR AND PROCEEDED TO THE FIELD VFR (AND PROBABLY MY LAST!). I REALIZE THAT EITHER VFR OR IFR; 'SEE AND AVOID' IS PLT RESPONSIBILITY -- WX PERMITTING.