Narrative:

I was assigned a heading of 340 degrees at 3000 ft until established on the ILS runway 35R and cleared for the approach when I noticed the needle swing through the HSI. As I turned to join the localizer, I heard a pop and then a spotter, and felt a slight yaw just like in training when your instructor shuts off the fuel selector to simulate an engine failure. After leveling off, I noticed the directional gyro had processed, so I reset it and turned to correct my course. Approach then instructed me to contact tower. Tower cleared me to land and worried about the reported freezing rain. I asked about the runway condition. They told me it was just wet. About that time the GS was about to center, so I lowered the landing gear and started down the ILS. I checked to make sure the fuel controls were in the on position when I noticed smoke filling the cockpit from the floor. I quickly shut the heat off, but chose to leave the master switch on, since I needed the electricity to finish shooting the approach. I decided it was better to fly the airplane and worry on the ground. The smoke had now gone and everything seemed under control. Tower then cleared me to taxi to parking, so I taxied in and never reported a problem. The aircraft had just been inspected for an airworthiness directive on a bolt on the engine accessory gear. Because of a distraction/misunderstanding, the nuts on the left magneto weren't torqued. The engine was runup and tested ok. It also checked ok during my before takeoff runup. During flight, the nuts gradually loosened, creating an oil leak and eventually allowed the magneto to fall off of the engine. Once it was dry of oil, the engine began to seize and threw a connecting rod(south). Smoke from the engine was then carried in the slipstream and into the fresh air vent in the tail, thus explaining the smoke in the cockpit.

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Original NASA ASRS Text

Title: A PA23-250 AT 3000 FT ON 10 MI FINAL HAS L ENG FAIL WITH SMOKE IN THE COCKPIT CAUSED BY A L MAGNETO MOUNT BOLT INSTALLED FINGER TIGHT.

Narrative: I WAS ASSIGNED A HDG OF 340 DEGS AT 3000 FT UNTIL ESTABLISHED ON THE ILS RWY 35R AND CLRED FOR THE APCH WHEN I NOTICED THE NEEDLE SWING THROUGH THE HSI. AS I TURNED TO JOIN THE LOC, I HEARD A POP AND THEN A SPOTTER, AND FELT A SLIGHT YAW JUST LIKE IN TRAINING WHEN YOUR INSTRUCTOR SHUTS OFF THE FUEL SELECTOR TO SIMULATE AN ENG FAILURE. AFTER LEVELING OFF, I NOTICED THE DIRECTIONAL GYRO HAD PROCESSED, SO I RESET IT AND TURNED TO CORRECT MY COURSE. APCH THEN INSTRUCTED ME TO CONTACT TWR. TWR CLRED ME TO LAND AND WORRIED ABOUT THE RPTED FREEZING RAIN. I ASKED ABOUT THE RWY CONDITION. THEY TOLD ME IT WAS JUST WET. ABOUT THAT TIME THE GS WAS ABOUT TO CTR, SO I LOWERED THE LNDG GEAR AND STARTED DOWN THE ILS. I CHKED TO MAKE SURE THE FUEL CTLS WERE IN THE ON POS WHEN I NOTICED SMOKE FILLING THE COCKPIT FROM THE FLOOR. I QUICKLY SHUT THE HEAT OFF, BUT CHOSE TO LEAVE THE MASTER SWITCH ON, SINCE I NEEDED THE ELECTRICITY TO FINISH SHOOTING THE APCH. I DECIDED IT WAS BETTER TO FLY THE AIRPLANE AND WORRY ON THE GND. THE SMOKE HAD NOW GONE AND EVERYTHING SEEMED UNDER CTL. TWR THEN CLRED ME TO TAXI TO PARKING, SO I TAXIED IN AND NEVER RPTED A PROB. THE ACFT HAD JUST BEEN INSPECTED FOR AN AIRWORTHINESS DIRECTIVE ON A BOLT ON THE ENG ACCESSORY GEAR. BECAUSE OF A DISTR/MISUNDERSTANDING, THE NUTS ON THE L MAGNETO WEREN'T TORQUED. THE ENG WAS RUNUP AND TESTED OK. IT ALSO CHKED OK DURING MY BEFORE TKOF RUNUP. DURING FLT, THE NUTS GRADUALLY LOOSENED, CREATING AN OIL LEAK AND EVENTUALLY ALLOWED THE MAGNETO TO FALL OFF OF THE ENG. ONCE IT WAS DRY OF OIL, THE ENG BEGAN TO SEIZE AND THREW A CONNECTING ROD(S). SMOKE FROM THE ENG WAS THEN CARRIED IN THE SLIPSTREAM AND INTO THE FRESH AIR VENT IN THE TAIL, THUS EXPLAINING THE SMOKE IN THE COCKPIT.

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.