Narrative:

I was involved in a near midair incident. The incident occurred approximately 7 mi nnw of rock county airport in janesville, wi. At the time of the incident, I was being worked by rockford, il approach control on 126.0 MHZ. I had descended from cruise altitude to an assigned altitude of 2700', the initial approach altitude for the ILS runway 4 approach that I was being vectored to. At the time of the incident I was in IMC. I had entered the clouds at approximately 6000 and was flying through a layer of clouds of greater than 9/10 coverage. The bases were at approximately 2000'. Janesville's ATIS was reporting an 1100' overcast, 4 mi visibility in fog. I was on an assigned heading of 220 degree. At approximately XX30Z I was informed of VFR traffic at 10 O'clock, 4 mi at 2300'. My response to the controller was that I was in instrument meteorological conditions. I was then informed, traffic climbing 2500', directly beneath you. Again, I responded that I was 'IMC'. A few seconds after my last radio transmission, I caught a glimpse of a tan, low wing airplane off of my left rear quarter. This aircraft was at my altitude and was going from my left to right. There were 2 passenger in the airplane with me. My eldest daughter was in the right rear seat and a CFI friend was in the right front seat. The CFI identified this aircraft as a tan small aircraft. My daughter observed a tan, low wing aircraft with possibly maroon trim. Both passenger said that the small aircraft was heading approximately 330 degree and climbing. Both said that it was well within 1/2 mi. We were unable to read the tail number as we were back in the clouds within seconds. The total time from exiting one cloud to entering the next is estimated at 15 seconds. There is no possible way that this small aircraft could have maintained VFR cloud separation minimums where this near midair occurred. After landing, I called the tower at janesville and discussed the incident with them. They told me that they had been in contact with rockford approach control and were aware of the incident. They also informed me that an small aircraft, same make, had departed janesville just prior to the incident and they thought they knew who it was. I then called rockford approach control and talked to the tower cabin attendant supervisor who was also the approach control supervisor. We discussed the incident and I was told that the small aircraft turned off his transponder right after the conflict. I filed a report by telephone with the supervisor at rockford. After reaching my home base that afternoon I purposely taxied past a same small aircraft to put it in the same prospective as the one in the incident. I now feel that the separation between the 2 airplanes was less than 1/4 mi. I believe that this incident occurred because the pilot of the small aircraft was 'skud running'. Separation between the clouds was less than 1/2 mi and vertical development was approximately 4000'. I doubt seriously, that if the small aircraft could have gone vertical, that he could have maintained VFR cloud clrncs. I feel that I heard some surprise and apprehension in the controller's voice after my first response of being in 'IMC'. No evasive action was recommended or taken. It may have been possible for the controller to have issued an evasive action recommendation had he realized that we were 'IMC' and that the small aircraft was not VFR. By the time that I observed the other airplane he was behind us and evasive action was no longer appropriate.

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Original NASA ASRS Text

Title: SMA PLT ON IFR FLT PLAN IN IMC EXPERIENCED NMAC WITH SMA SUPPOSEDLY VFR.

Narrative: I WAS INVOLVED IN A NEAR MIDAIR INCIDENT. THE INCIDENT OCCURRED APPROX 7 MI NNW OF ROCK COUNTY ARPT IN JANESVILLE, WI. AT THE TIME OF THE INCIDENT, I WAS BEING WORKED BY ROCKFORD, IL APCH CTL ON 126.0 MHZ. I HAD DESCENDED FROM CRUISE ALT TO AN ASSIGNED ALT OF 2700', THE INITIAL APCH ALT FOR THE ILS RWY 4 APCH THAT I WAS BEING VECTORED TO. AT THE TIME OF THE INCIDENT I WAS IN IMC. I HAD ENTERED THE CLOUDS AT APPROX 6000 AND WAS FLYING THROUGH A LAYER OF CLOUDS OF GREATER THAN 9/10 COVERAGE. THE BASES WERE AT APPROX 2000'. JANESVILLE'S ATIS WAS REPORTING AN 1100' OVERCAST, 4 MI VISIBILITY IN FOG. I WAS ON AN ASSIGNED HDG OF 220 DEG. AT APPROX XX30Z I WAS INFORMED OF VFR TFC AT 10 O'CLOCK, 4 MI AT 2300'. MY RESPONSE TO THE CTLR WAS THAT I WAS IN INSTRUMENT METEOROLOGICAL CONDITIONS. I WAS THEN INFORMED, TFC CLIMBING 2500', DIRECTLY BENEATH YOU. AGAIN, I RESPONDED THAT I WAS 'IMC'. A FEW SECONDS AFTER MY LAST RADIO XMISSION, I CAUGHT A GLIMPSE OF A TAN, LOW WING AIRPLANE OFF OF MY LEFT REAR QUARTER. THIS ACFT WAS AT MY ALT AND WAS GOING FROM MY LEFT TO RIGHT. THERE WERE 2 PAX IN THE AIRPLANE WITH ME. MY ELDEST DAUGHTER WAS IN THE RIGHT REAR SEAT AND A CFI FRIEND WAS IN THE RIGHT FRONT SEAT. THE CFI IDENTIFIED THIS ACFT AS A TAN SMA. MY DAUGHTER OBSERVED A TAN, LOW WING ACFT WITH POSSIBLY MAROON TRIM. BOTH PAX SAID THAT THE SMA WAS HDG APPROX 330 DEG AND CLIMBING. BOTH SAID THAT IT WAS WELL WITHIN 1/2 MI. WE WERE UNABLE TO READ THE TAIL NUMBER AS WE WERE BACK IN THE CLOUDS WITHIN SECONDS. THE TOTAL TIME FROM EXITING ONE CLOUD TO ENTERING THE NEXT IS ESTIMATED AT 15 SECONDS. THERE IS NO POSSIBLE WAY THAT THIS SMA COULD HAVE MAINTAINED VFR CLOUD SEPARATION MINIMUMS WHERE THIS NEAR MIDAIR OCCURRED. AFTER LNDG, I CALLED THE TWR AT JANESVILLE AND DISCUSSED THE INCIDENT WITH THEM. THEY TOLD ME THAT THEY HAD BEEN IN CONTACT WITH ROCKFORD APCH CTL AND WERE AWARE OF THE INCIDENT. THEY ALSO INFORMED ME THAT AN SMA, SAME MAKE, HAD DEPARTED JANESVILLE JUST PRIOR TO THE INCIDENT AND THEY THOUGHT THEY KNEW WHO IT WAS. I THEN CALLED ROCKFORD APCH CTL AND TALKED TO THE TWR CAB SUPVR WHO WAS ALSO THE APCH CTL SUPVR. WE DISCUSSED THE INCIDENT AND I WAS TOLD THAT THE SMA TURNED OFF HIS XPONDER RIGHT AFTER THE CONFLICT. I FILED A REPORT BY TELEPHONE WITH THE SUPVR AT ROCKFORD. AFTER REACHING MY HOME BASE THAT AFTERNOON I PURPOSELY TAXIED PAST A SAME SMA TO PUT IT IN THE SAME PROSPECTIVE AS THE ONE IN THE INCIDENT. I NOW FEEL THAT THE SEPARATION BETWEEN THE 2 AIRPLANES WAS LESS THAN 1/4 MI. I BELIEVE THAT THIS INCIDENT OCCURRED BECAUSE THE PLT OF THE SMA WAS 'SKUD RUNNING'. SEPARATION BETWEEN THE CLOUDS WAS LESS THAN 1/2 MI AND VERTICAL DEVELOPMENT WAS APPROX 4000'. I DOUBT SERIOUSLY, THAT IF THE SMA COULD HAVE GONE VERTICAL, THAT HE COULD HAVE MAINTAINED VFR CLOUD CLRNCS. I FEEL THAT I HEARD SOME SURPRISE AND APPREHENSION IN THE CTLR'S VOICE AFTER MY FIRST RESPONSE OF BEING IN 'IMC'. NO EVASIVE ACTION WAS RECOMMENDED OR TAKEN. IT MAY HAVE BEEN POSSIBLE FOR THE CTLR TO HAVE ISSUED AN EVASIVE ACTION RECOMMENDATION HAD HE REALIZED THAT WE WERE 'IMC' AND THAT THE SMA WAS NOT VFR. BY THE TIME THAT I OBSERVED THE OTHER AIRPLANE HE WAS BEHIND US AND EVASIVE ACTION WAS NO LONGER APPROPRIATE.

Data retrieved from NASA's ASRS site as of August 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.