Narrative:

En route detroit city to new york city, east of dunkirk VOR, the engine started running rough at 11000'. I assumed induction icing, although alternate air made little difference. Requested clear to 9000' and the engine smoothed out at 9000'. 20 mi or so east of dunkirk engine started running rough again. Advised center that I could not maintain altitude and requested 7000'. Cleared to 7. At 7000' still could not maintain altitude and the frequency was busy with center talking to other airplanes. Descended through 6700'. Advised center that I could not maintain altitude but did not declare an emergency and requested precautionary landing at johnson city. Center advised wellsville was 15 mi to southeast and suggested an approach there. Center cleared me down to various altitudes en route wellsville which I was unable to maintain. I never declared an emergency, however center appeared to be treating it a one. Eventually cleared to 3500', which I could not maintain. However, I had intercepted the G/south. At this point, descended to 2.5 where altitude could be maintained. By this time had lost touch with center due to low altitude, but was talking to another aircraft in the area on the frequency. I missed the approach, but at approximately 2000-2500' was in contact with the ground at all times with only 1/2 mi visibility. The other pilot, who was familiar with wellsville, directed me via various landmarks back towellsville and then to the airport using the center frequency. I landed and the mechanic discovered a faulty magneto and one magneto on which the timing gap had become too narrow. The mags had started to gap at high altitude and created tracks which continued to gap after descent. ZOB was most helpful and I never felt my life was in danger at any time. Assistance at low altitude of the other pilot in the area was most reassuring and contributed to the successful termination of the flight.

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Original NASA ASRS Text

Title: COMPLEX SMA MAKES EMERGENCY LNDG DUE ENGINE TROUBLE.

Narrative: ENRTE DETROIT CITY TO NEW YORK CITY, E OF DUNKIRK VOR, THE ENG STARTED RUNNING ROUGH AT 11000'. I ASSUMED INDUCTION ICING, ALTHOUGH ALTERNATE AIR MADE LITTLE DIFFERENCE. REQUESTED CLR TO 9000' AND THE ENG SMOOTHED OUT AT 9000'. 20 MI OR SO E OF DUNKIRK ENG STARTED RUNNING ROUGH AGAIN. ADVISED CENTER THAT I COULD NOT MAINTAIN ALT AND REQUESTED 7000'. CLRED TO 7. AT 7000' STILL COULD NOT MAINTAIN ALT AND THE FREQ WAS BUSY WITH CENTER TALKING TO OTHER AIRPLANES. DSNDED THROUGH 6700'. ADVISED CENTER THAT I COULD NOT MAINTAIN ALT BUT DID NOT DECLARE AN EMER AND REQUESTED PRECAUTIONARY LNDG AT JOHNSON CITY. CENTER ADVISED WELLSVILLE WAS 15 MI TO SE AND SUGGESTED AN APCH THERE. CENTER CLRED ME DOWN TO VARIOUS ALTS ENRTE WELLSVILLE WHICH I WAS UNABLE TO MAINTAIN. I NEVER DECLARED AN EMER, HOWEVER CENTER APPEARED TO BE TREATING IT A ONE. EVENTUALLY CLRED TO 3500', WHICH I COULD NOT MAINTAIN. HOWEVER, I HAD INTERCEPTED THE G/S. AT THIS POINT, DSNDED TO 2.5 WHERE ALT COULD BE MAINTAINED. BY THIS TIME HAD LOST TOUCH WITH CENTER DUE TO LOW ALT, BUT WAS TALKING TO ANOTHER ACFT IN THE AREA ON THE FREQ. I MISSED THE APCH, BUT AT APPROX 2000-2500' WAS IN CONTACT WITH THE GND AT ALL TIMES WITH ONLY 1/2 MI VISIBILITY. THE OTHER PLT, WHO WAS FAMILIAR WITH WELLSVILLE, DIRECTED ME VIA VARIOUS LANDMARKS BACK TOWELLSVILLE AND THEN TO THE ARPT USING THE CENTER FREQ. I LANDED AND THE MECH DISCOVERED A FAULTY MAGNETO AND ONE MAGNETO ON WHICH THE TIMING GAP HAD BECOME TOO NARROW. THE MAGS HAD STARTED TO GAP AT HIGH ALT AND CREATED TRACKS WHICH CONTINUED TO GAP AFTER DSCNT. ZOB WAS MOST HELPFUL AND I NEVER FELT MY LIFE WAS IN DANGER AT ANY TIME. ASSISTANCE AT LOW ALT OF THE OTHER PLT IN THE AREA WAS MOST REASSURING AND CONTRIBUTED TO THE SUCCESSFUL TERMINATION OF THE FLT.

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.