Narrative:

The problem arose while climbing through 3700' on the way up to my final cruising altitude of 4500'. I discovered by listening that the engine was running rough or missing, as if carburetor ice had formed, or if the spark plugs were badly fouled. I immediately applied carburetor heat (full), which seemed to help a bit. I also applied full throttle momentarily in an effort to improve the situation after a few mins with full carburetor heat on, the problem became much worse. The engine RPM's began to drop, and I became worried that the engine might quit. I applied mixture rich, and advised my approach that I was declaring an emergency due to substantial engine roughness. I asked for vectors to the nearest airport, which approach pointed out to be 44N, sky acres, millbrook, ny. I executed a standard lhand pattern entry and short field landing. All phases of the pattern and subsequent landing were normal. After landing, I contacted my approach by radio and advised that all was well. Contributing factors. Contributing to the problem were the following factors (as determined by the engine). Badly fouled spark plugs, 2 out of 8 very badly fouled. Coil in right magneto breaking down when hot. Failure to create proper sparking voltages/potentials. Corrective actions attempted in flight (during emergency) were previously described. Corrective action. Corrective action on the ground consisted of reconditioning the spark plugs and performing a run up. All run up indications were normal, except when the right magneto was selected, the engine was very rough. The right magneto was removed and visly inspected. No visible defect could be found. The right magneto was replaced, and engine run up was performed. All indications were normal. Human performance considerations. My perception at the time of the problem was that a serious engine problem had developed suddenly. I had already flown a long leg flight from bed-bdl earlier in the morning west/O indication of any problem. The suddenness of the problem led me to believe that things were happening quickly. I decided that the best and safest action was to land immediately. I had been recieving VFR radar advisories from my approach at the time the problem occurred, and I advised them that I was declaring an emergency due to substantial engine roughness. The reason that I declared an emergency was that a first engine failure was emminent, and I wanted to avail myself of all available ATC services and assistance, as well as conform to the maximum that if the safety of the flight is in doubt, declare first, explain later. My inaction in flight during the emergency as to check the magnetos by selecting each one in turn to see if the engine smoothed out. I was concerned that I might lose the engine all together if I switched magnetos, so I decided not to, and elected to expedite landing. The decision not to switch mags was based primarily on my having read accident reports wherein one magnetic was already performing marginally, and when the other magnetic was selected (the really bad one), the engine quit.

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Original NASA ASRS Text

Title: SMA EXPERIENCES SEVERE ENGINE ROUGHNESS ON CLIMBOUT AND MAKES PRECAUTIONARY LNDG WITH ASSISTANCE FROM ATC. EMERGENCY DECLARED.

Narrative: THE PROB AROSE WHILE CLBING THROUGH 3700' ON THE WAY UP TO MY FINAL CRUISING ALT OF 4500'. I DISCOVERED BY LISTENING THAT THE ENG WAS RUNNING ROUGH OR MISSING, AS IF CARB ICE HAD FORMED, OR IF THE SPARK PLUGS WERE BADLY FOULED. I IMMEDIATELY APPLIED CARB HEAT (FULL), WHICH SEEMED TO HELP A BIT. I ALSO APPLIED FULL THROTTLE MOMENTARILY IN AN EFFORT TO IMPROVE THE SITUATION AFTER A FEW MINS WITH FULL CARB HEAT ON, THE PROB BECAME MUCH WORSE. THE ENG RPM'S BEGAN TO DROP, AND I BECAME WORRIED THAT THE ENG MIGHT QUIT. I APPLIED MIXTURE RICH, AND ADVISED MY APCH THAT I WAS DECLARING AN EMER DUE TO SUBSTANTIAL ENG ROUGHNESS. I ASKED FOR VECTORS TO THE NEAREST ARPT, WHICH APCH POINTED OUT TO BE 44N, SKY ACRES, MILLBROOK, NY. I EXECUTED A STANDARD LHAND PATTERN ENTRY AND SHORT FIELD LNDG. ALL PHASES OF THE PATTERN AND SUBSEQUENT LNDG WERE NORMAL. AFTER LNDG, I CONTACTED MY APCH BY RADIO AND ADVISED THAT ALL WAS WELL. CONTRIBUTING FACTORS. CONTRIBUTING TO THE PROB WERE THE FOLLOWING FACTORS (AS DETERMINED BY THE ENG). BADLY FOULED SPARK PLUGS, 2 OUT OF 8 VERY BADLY FOULED. COIL IN R MAGNETO BREAKING DOWN WHEN HOT. FAILURE TO CREATE PROPER SPARKING VOLTAGES/POTENTIALS. CORRECTIVE ACTIONS ATTEMPTED IN FLT (DURING EMER) WERE PREVIOUSLY DESCRIBED. CORRECTIVE ACTION. CORRECTIVE ACTION ON THE GND CONSISTED OF RECONDITIONING THE SPARK PLUGS AND PERFORMING A RUN UP. ALL RUN UP INDICATIONS WERE NORMAL, EXCEPT WHEN THE R MAGNETO WAS SELECTED, THE ENG WAS VERY ROUGH. THE R MAGNETO WAS REMOVED AND VISLY INSPECTED. NO VISIBLE DEFECT COULD BE FOUND. THE R MAGNETO WAS REPLACED, AND ENG RUN UP WAS PERFORMED. ALL INDICATIONS WERE NORMAL. HUMAN PERFORMANCE CONSIDERATIONS. MY PERCEPTION AT THE TIME OF THE PROB WAS THAT A SERIOUS ENG PROB HAD DEVELOPED SUDDENLY. I HAD ALREADY FLOWN A LONG LEG FLT FROM BED-BDL EARLIER IN THE MORNING W/O INDICATION OF ANY PROB. THE SUDDENNESS OF THE PROB LED ME TO BELIEVE THAT THINGS WERE HAPPENING QUICKLY. I DECIDED THAT THE BEST AND SAFEST ACTION WAS TO LAND IMMEDIATELY. I HAD BEEN RECIEVING VFR RADAR ADVISORIES FROM MY APCH AT THE TIME THE PROB OCCURRED, AND I ADVISED THEM THAT I WAS DECLARING AN EMER DUE TO SUBSTANTIAL ENG ROUGHNESS. THE REASON THAT I DECLARED AN EMER WAS THAT A FIRST ENG FAILURE WAS EMMINENT, AND I WANTED TO AVAIL MYSELF OF ALL AVAILABLE ATC SVCS AND ASSISTANCE, AS WELL AS CONFORM TO THE MAX THAT IF THE SAFETY OF THE FLT IS IN DOUBT, DECLARE FIRST, EXPLAIN LATER. MY INACTION IN FLT DURING THE EMER AS TO CHK THE MAGNETOS BY SELECTING EACH ONE IN TURN TO SEE IF THE ENG SMOOTHED OUT. I WAS CONCERNED THAT I MIGHT LOSE THE ENG ALL TOGETHER IF I SWITCHED MAGNETOS, SO I DECIDED NOT TO, AND ELECTED TO EXPEDITE LNDG. THE DECISION NOT TO SWITCH MAGS WAS BASED PRIMARILY ON MY HAVING READ ACCIDENT RPTS WHEREIN ONE MAG WAS ALREADY PERFORMING MARGINALLY, AND WHEN THE OTHER MAG WAS SELECTED (THE REALLY BAD ONE), THE ENG QUIT.

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.