Narrative:

I had taken off from janesville, wi, climbing out of 1200 ft, when I realized that the airspeed indicator was indicating incorrectly. It was VFR, and tops were reported to be 5000 ft in that area. I continued climbing and recycled the pitot heat. At approximately 4000 ft, chicago center requested my altitude. I told ATC to standby. They responded that they would like me to report my altitude every 1000 ft, and to expedite to 11000 ft due to milwaukee airspace. At that time I responded to ATC that I was having an altimeter problem and could not make that report. ATC asked me if I could estimate my altitude. The tops had just been reported at 9000 ft, and since I was well on top, I estimated 10500 ft. ATC asked if I would like to continue, and I said yes. A few mins later a controller told me they could not guarantee my altitude. She then told me I could continue VFR on top if I could maintain VFR, and if this were not possible, to let them know. After leveling off, I cycled the alternate static air source, and the altimeter reading increased 3000 ft. It was now indicating 13000 ft. ATC asked me to verify my altitude, and I reported 13000 ft. ATC then asked if I could descend to 12500 ft, and I responded that I could. I began a timed 500 FPM descend to 12500 ft. I continued the flight as we crossed lake michigan, and on nearing grand rapids, mi, an air carrier commuter called ATC and asked if they were showing any traffic in his 12 O'clock position and 1700 ft above him. ATC responded in the negative, but said they did have a twin small transport at 10500 ft, and asked the commuter to stand by. Again ATC responded that they had a twin small transport with an estimated altitude of 10500 ft. The commuter said the traffic had just come up on his TCASII and was indicating 12500 ft. I looked off my right wing and saw the commuter, and told ATC I could confirm he was below us and that the altitude appeared to check.

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Original NASA ASRS Text

Title: AN SMT PISTON FREIGHTER HAD A PROBLEM WITH ITS PITOT STATIC SYS. IT CHOSE TO CONTINUE ITS TRIP IN VMC.

Narrative: I HAD TAKEN OFF FROM JANESVILLE, WI, CLBING OUT OF 1200 FT, WHEN I REALIZED THAT THE AIRSPD INDICATOR WAS INDICATING INCORRECTLY. IT WAS VFR, AND TOPS WERE RPTED TO BE 5000 FT IN THAT AREA. I CONTINUED CLBING AND RECYCLED THE PITOT HEAT. AT APPROX 4000 FT, CHICAGO CTR REQUESTED MY ALT. I TOLD ATC TO STANDBY. THEY RESPONDED THAT THEY WOULD LIKE ME TO RPT MY ALT EVERY 1000 FT, AND TO EXPEDITE TO 11000 FT DUE TO MILWAUKEE AIRSPACE. AT THAT TIME I RESPONDED TO ATC THAT I WAS HAVING AN ALTIMETER PROBLEM AND COULD NOT MAKE THAT RPT. ATC ASKED ME IF I COULD ESTIMATE MY ALT. THE TOPS HAD JUST BEEN RPTED AT 9000 FT, AND SINCE I WAS WELL ON TOP, I ESTIMATED 10500 FT. ATC ASKED IF I WOULD LIKE TO CONTINUE, AND I SAID YES. A FEW MINS LATER A CTLR TOLD ME THEY COULD NOT GUARANTEE MY ALT. SHE THEN TOLD ME I COULD CONTINUE VFR ON TOP IF I COULD MAINTAIN VFR, AND IF THIS WERE NOT POSSIBLE, TO LET THEM KNOW. AFTER LEVELING OFF, I CYCLED THE ALTERNATE STATIC AIR SOURCE, AND THE ALTIMETER READING INCREASED 3000 FT. IT WAS NOW INDICATING 13000 FT. ATC ASKED ME TO VERIFY MY ALT, AND I RPTED 13000 FT. ATC THEN ASKED IF I COULD DSND TO 12500 FT, AND I RESPONDED THAT I COULD. I BEGAN A TIMED 500 FPM DSND TO 12500 FT. I CONTINUED THE FLT AS WE CROSSED LAKE MICHIGAN, AND ON NEARING GRAND RAPIDS, MI, AN ACR COMMUTER CALLED ATC AND ASKED IF THEY WERE SHOWING ANY TFC IN HIS 12 O'CLOCK POS AND 1700 FT ABOVE HIM. ATC RESPONDED IN THE NEGATIVE, BUT SAID THEY DID HAVE A TWIN SMT AT 10500 FT, AND ASKED THE COMMUTER TO STAND BY. AGAIN ATC RESPONDED THAT THEY HAD A TWIN SMT WITH AN ESTIMATED ALT OF 10500 FT. THE COMMUTER SAID THE TFC HAD JUST COME UP ON HIS TCASII AND WAS INDICATING 12500 FT. I LOOKED OFF MY R WING AND SAW THE COMMUTER, AND TOLD ATC I COULD CONFIRM HE WAS BELOW US AND THAT THE ALT APPEARED TO CHK.

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.