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 local, then 3000-4000 ft broken to scattered in south illinois. So the plan was for VFR at about 3000 ft MSL. Encountering some scattered clouds south of pnt, I descended to 2500 ft, no problem. After calling decatur tower for transition through class D about 10-11 mi north, I realized the scattered to broken layer was becoming lower and of a conflict between 500 ft cloud clearance and 1000 ft obstacle clearance from two 1000 ft plus towers (1728 ft and 2000 ft MSL) 8 mi north 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 tower requested a position update because of possible lear traffic, presumably being handed off by champaign approach. I replied that position was by tall towers, north. About half a min later I saw the lear passing below and behind me from the west, followed shortly by his calling decatur tower on a (about 5-6 mi) right base for runway 24, and advising tower of a cessna north (me), at less than minimum cloud clearance 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 deviation and priority descent as a solution to the cloud clearance/obstacle clearance conflict -- a mental set of 'staying the course.' the 1046 ft and 1314 ft towers on V-313, 8 mi north of decatur airport are a bad thing in general, and were, in this circumstance, an absorbing distraction. One might also wonder if the lear was on vectors for descent through scattered broken clouds, and if so, was he not advised of my VFR mode C target? Also, would (cmi) approach vector a jet through scattered/broken clouds to 2500 ft MSL within 2 or 3 mi from 2000 ft MSL towers (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 east and advise decatur upon realizing the required descending was going to be in conflict with obstacle clearance (the east tower 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 flight planning and procedures for this type of contingency. Although it's the pilot's responsibility to assure appropriate obstacle clearance at all times, it might be a good practice for decatur tower to issue a routine caution reminder of the towers to VFR's transitioning to or from directly north. I've heard this done at other ATC facilities, eg, green bay, wi, which has similar towers about 10 mi to the southeast.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.