C172 PLT ON AN IFR FLT PLAN ANTICIPATES VFR CONDITIONS AND IS UNPREPARED FOR AN AMENDED CLRNC ENRTE.

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I HAD BRIEFED WITH WX BEFORE DEP ON A XCOUNTRY AND WAS ADVISED OF A POSSIBLE NARROW BAND OF MVFR ENRTE; WITH VFR EXPECTED THROUGH THE RTE AND FLT. I DECIDED TO FILE IFR DIRECT IN THE EVENT THE POSSIBLE MVFR BECAME ACTUAL. I WAS IN THE FLYING CLUB C172 WITH A GPS I HAD NOT MASTERED. MY LOGIC AND PLANNING WERE FAULTY ON SEVERAL POINTS: 1) ITS VFR; ITS GPS DIRECT; NO APCHS; NO PROB; 2) I NEGLECTED TO NOTE 'NO SIDS/STARS' ON THE REQUEST; AND 3) MINIMAL PLANNING FOR CONTINGENCIES. APPROX 75 MI S OF DEST; THE FLT HAD BEEN AND CONTINUED TO BE VFR AND UNEVENTFUL. SOON AFTER CONTACT WITH CMI APCH IN THEIR CLASS C AIRSPACE; APCH ADVISED ME OF AN AMENDED CLRNC. I HAD BEEN FOLLOWING FLT PROGRESS ON VFR CHARTS; AND WAS TOTALLY UNPREPARED FOR THIS EVENT. CONFUSION REIGNED IN THE COCKPIT AS I FUMBLED FOR THE CORRECT PUBS AND TRIED TO REPROGRAM THE GPS; DIRECTIONAL CTL SUFFERED; ALT CTL WAS ERRATIC. I WAS UNABLE TO PROMPTLY RESPOND TO THE NEW CLRNC; FIND THE APPROPRIATE PUBS; OR REPROGRAM THE GPS. I HAD NOT ACCEPTED THE NEW CLRNC AND ATTEMPTED TO CANCEL MY IFR AND CONTINUE VFR BUT COULDN'T RAISE APCH OR WAS ADVISED TO STAND BY. WHEN NEXT IN TOUCH WITH APCH; THEY ADVISED THAT THEY HAD BEEN ON THE PHONE WITH CHICAGO APCH AND THEY HAD APPROVED MY CONTINUING ON ORIGINAL COURSE/PLAN AND WAS CLRED DIRECT THEN HANDED OFF TO ZAU. AT TIME THE FLT RETURNED TO SOME DEGREE OF NORMALCY. SHORTLY I WAS CLRED FOR A VISUAL APCH TO MY DEST; I CANCELED IFR; DSNDED TO VFR ALT AND COMPLETED THE FLT WITHOUT FURTHER INCIDENT. THIS CHAIN OF EVENTS BEGAN WITH ERRONEOUS ASSUMPTIONS; INCOMPLETE PLANNING; INADEQUATE PREPARATION; INADEQUATE FAMILIARITY WITH NAV EQUIP AND A BAD CASE OF 'GET THEREITIS.' THE ONLY BRIGHT POINT IN THIS FIASCO IS IT TOOK PLACE IN VFR AND REMAINED OUTSIDE CHICAGO CLASS B AIRSPACE. FUTURE IFR FLT PLANS MUST BE MADE AS IF IT WERE MAJOR IFR ENRTE AND EXPECT AND BE PREPARED FOR ANY CONTINGENCY WHICH MIGHT ARISE. ADDITIONALLY; ONE MUST HAVE A FIRM GRASP ON THE OPERATIONAL EQUIP TO BE USED.