Narrative:

The flight from buffalo, mn (842) to ane was uneventful. The aircraft was shut down for about 15 mins. The WX was clear, calm wind, and about 40 degrees F temperature. Start-up and taxi were normal. During the runup, a rough running magnetic was noted. I leaned the mixture per company procedures, and the problem appeared to have cleared itself up. Takeoff (runway 26) and climb out were normal. About 7 mi northeast of microphone I established contact with the tower controller, since we would pass over gep VOR, and it is nice to receive reports of traffic practicing the VOR-a into microphone. As we passed directly over the VOR, I was about to report outbnd form the VOR when the engine (which had run flawlessly up to this point) sputtered and seemed as though it would quite. I grabbed the throttle and pulled it back to idle, and the engine seemed to idle fine. Repeated attempts to increase RPM beyond 1200 failed. I established a 60 KT glide and called microphone tower for alternatives. While they were responding I completed an emergency checklist and eyeballed many possible landing sites, given the calm wind. Then I reported a partial engine failure, but did not declare an emergency. The problem with the engine, I thought, may be that the engine was flooding. I leaned the mixture and tried the throttle again. The problem was no better. I checked the magnetos and the right magnetic sounded better, so I left the key there. I saw that I would not be able to extend my glide to microphone, so I chose a field and reported my intentions to the tower controller. I landed on a plowed bean field, lightly snow covered (patches), with full flaps and the engine idling. No damage to the aircraft nor the field was evident. I told microphone tower we were safe on the ground, and they requested we call them as soon as possible. Problem: magneto coils intermittent, both failed simultaneously. Better guidelines for magneto preventive maintenance might prevent a recurrence.

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Original NASA ASRS Text

Title: FORCED LNDG AS SMA ENGINE LOSES POWER. OFF ARPT LNDG.

Narrative: THE FLT FROM BUFFALO, MN (842) TO ANE WAS UNEVENTFUL. THE ACFT WAS SHUT DOWN FOR ABOUT 15 MINS. THE WX WAS CLR, CALM WIND, AND ABOUT 40 DEGS F TEMP. START-UP AND TAXI WERE NORMAL. DURING THE RUNUP, A ROUGH RUNNING MAG WAS NOTED. I LEANED THE MIXTURE PER COMPANY PROCS, AND THE PROB APPEARED TO HAVE CLRED ITSELF UP. TKOF (RWY 26) AND CLBOUT WERE NORMAL. ABOUT 7 MI NE OF MIC I ESTABLISHED CONTACT WITH THE TWR CTLR, SINCE WE WOULD PASS OVER GEP VOR, AND IT IS NICE TO RECEIVE RPTS OF TFC PRACTICING THE VOR-A INTO MIC. AS WE PASSED DIRECTLY OVER THE VOR, I WAS ABOUT TO RPT OUTBND FORM THE VOR WHEN THE ENG (WHICH HAD RUN FLAWLESSLY UP TO THIS POINT) SPUTTERED AND SEEMED AS THOUGH IT WOULD QUITE. I GRABBED THE THROTTLE AND PULLED IT BACK TO IDLE, AND THE ENG SEEMED TO IDLE FINE. REPEATED ATTEMPTS TO INCREASE RPM BEYOND 1200 FAILED. I ESTABLISHED A 60 KT GLIDE AND CALLED MIC TWR FOR ALTERNATIVES. WHILE THEY WERE RESPONDING I COMPLETED AN EMER CHKLIST AND EYEBALLED MANY POSSIBLE LNDG SITES, GIVEN THE CALM WIND. THEN I RPTED A PARTIAL ENG FAILURE, BUT DID NOT DECLARE AN EMER. THE PROB WITH THE ENG, I THOUGHT, MAY BE THAT THE ENG WAS FLOODING. I LEANED THE MIXTURE AND TRIED THE THROTTLE AGAIN. THE PROB WAS NO BETTER. I CHKED THE MAGNETOS AND THE RIGHT MAG SOUNDED BETTER, SO I LEFT THE KEY THERE. I SAW THAT I WOULD NOT BE ABLE TO EXTEND MY GLIDE TO MIC, SO I CHOSE A FIELD AND RPTED MY INTENTIONS TO THE TWR CTLR. I LANDED ON A PLOWED BEAN FIELD, LIGHTLY SNOW COVERED (PATCHES), WITH FULL FLAPS AND THE ENG IDLING. NO DAMAGE TO THE ACFT NOR THE FIELD WAS EVIDENT. I TOLD MIC TWR WE WERE SAFE ON THE GND, AND THEY REQUESTED WE CALL THEM ASAP. PROB: MAGNETO COILS INTERMITTENT, BOTH FAILED SIMULTANEOUSLY. BETTER GUIDELINES FOR MAGNETO PREVENTIVE MAINT MIGHT PREVENT A RECURRENCE.

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.