NMAC IN PROX OF CLASS D AIRSPACE.

Narrative

TRAVELING VFR FROM OSHKOSH; WI; TO EFFINGHAM; IL; I WAS CRUISING LOW (3000 FT MSL) TO MINIMIZE HEADWINDS. AN XAX10 AM CDT BRIEFING CALLED FOR 10000 FT SCATTERED TO XF00 LCL; THEN 3000-4000 FT BROKEN TO SCATTERED IN S ILLINOIS. SO THE PLAN WAS FOR VFR AT ABOUT 3000 FT MSL. ENCOUNTERING SOME SCATTERED CLOUDS S OF PNT; I DSNDED TO 2500 FT; NO PROB. AFTER CALLING DECATUR TWR FOR TRANSITION THROUGH CLASS D ABOUT 10-11 MI N; I REALIZED THE SCATTERED TO BROKEN LAYER WAS BECOMING LOWER AND OF A CONFLICT BTWN 500 FT CLOUD CLRNC AND 1000 FT OBSTACLE CLRNC FROM TWO 1000 FT PLUS TWRS (1728 FT AND 2000 FT MSL) 8 MI N OF DECATUR ON V-313. AT THIS POINT MY 2400 FT MSL WASN'T COMPLYING WITH EITHER REQUIREMENT. WHILE I WAS PROCESSING THIS DATA; DECATUR TWR REQUESTED A POS UPDATE BECAUSE OF POSSIBLE LEAR TFC; PRESUMABLY BEING HANDED OFF BY CHAMPAIGN APCH. I REPLIED THAT POS WAS BY TALL TWRS; N. ABOUT HALF A MIN LATER I SAW THE LEAR PASSING BELOW AND BEHIND ME FROM THE W; FOLLOWED SHORTLY BY HIS CALLING DECATUR TWR ON A (ABOUT 5-6 MI) R BASE FOR RWY 24; AND ADVISING TWR OF A CESSNA N (ME); AT LESS THAN MINIMUM CLOUD CLRNC FROM BASES. IT WAS A JOLT TO ME TO REALIZE THAT THIS WAS CORRECT; I HAD STILL BEEN PROBABLY ABOUT 100-200 FT BELOW THE CLOUDS. APPARENTLY HE HAD EXECUTED EVASIVE ACTION. THE PRIMARY FACTOR; OF COURSE; WAS MY LACK OF RECOGNIZING OR ACCEPTING A RADIAL COURSE DEV AND PRIORITY DSCNT AS A SOLUTION TO THE CLOUD CLRNC/OBSTACLE CLRNC CONFLICT -- A MENTAL SET OF 'STAYING THE COURSE.' THE 1046 FT AND 1314 FT TWRS ON V-313; 8 MI N OF DECATUR ARPT ARE A BAD THING IN GENERAL; AND WERE; IN THIS CIRCUMSTANCE; AN ABSORBING DISTR. ONE MIGHT ALSO WONDER IF THE LEAR WAS ON VECTORS FOR DSCNT THROUGH SCATTERED BROKEN CLOUDS; AND IF SO; WAS HE NOT ADVISED OF MY VFR MODE C TARGET? ALSO; WOULD (CMI) APCH VECTOR A JET THROUGH SCATTERED/BROKEN CLOUDS TO 2500 FT MSL WITHIN 2 OR 3 MI FROM 2000 FT MSL TWRS (THE MSA IS 3100 FT)? A COUPLE OF THOUGHT PROVOKING ADDITIONAL UNKNOWNS TO ME. THE OBVIOUS SOLUTION WAS FOR ME TO SIMPLY ALTER COURSE TO THE E AND ADVISE DECATUR UPON REALIZING THE REQUIRED DSNDING WAS GOING TO BE IN CONFLICT WITH OBSTACLE CLRNC (THE E TWR WAS IN SIGHT). THE MENTAL SET WAS TO MAINTAIN COURSE; WHICH; IN RETROSPECT; WAS NOT IMPORTANT. I FEEL SENSITIZED TO THIS NOW; AND EXPECT TO ADJUST FUTURE FLT PLANNING AND PROCS FOR THIS TYPE OF CONTINGENCY. ALTHOUGH IT'S THE PLT'S RESPONSIBILITY TO ASSURE APPROPRIATE OBSTACLE CLRNC AT ALL TIMES; IT MIGHT BE A GOOD PRACTICE FOR DECATUR TWR TO ISSUE A ROUTINE CAUTION REMINDER OF THE TWRS TO VFR'S TRANSITIONING TO OR FROM DIRECTLY N. I'VE HEARD THIS DONE AT OTHER ATC FACILITIES; EG; GREEN BAY; WI; WHICH HAS SIMILAR TWRS ABOUT 10 MI TO THE SE.