SMA PLT HAS ENG VIBRATION JUST AFTER TKOF. PRECAUTIONARY LNDG STRAIGHT AHEAD.

Narrative

HAD JUST RETURNED ACFT TO HOME BASE (07C) FOLLOWING MAJOR OVERHAUL. WAS TEST FLOWN OVER MECH'S AIRSTRIP FOR 45 MINS; LANDED TO CHK FOR LEAKS AND EXAMINE OIL FILTER FOR METAL. NO LEAKS; NO METAL DETECTED. NEW FILTER. ACFT RELEASED FOR FLT. 10 MIN FLT FROM THERE TO HOME BASE. ALL RUN-UPS WERE NORMAL AND FLT OPS NORMAL. LEFT ACFT AT HOME BASE TO RETURN TO MECH'S TO PICK UP MY CAR. UPON RETURN TO HOME BASE I WANTED TO FLY SOME MORE AND ASKED A PLT FRIEND IF HE WANTED TO GO ALONG. HE DID. RUN-UP WAS NORMAL; ENG SMOOTH. PLT FRIEND COMMENTED THAT ENG 'SOUNDS REAL GOOD.' ROLLOUT NORMAL; NO INDICATIONS OF ANYTHING WRONG. ROTATION NORMAL AND SMOOTH. UPON REACHING APPROX 400 FT AGL NOTICED A MILD VIBRATION COMING FROM UP FRONT. THOUGHT IT MIGHT BE FROM NOSEWHEEL STILL SPINNING. SUDDENLY BECAME A SEVERE VIBRATION AND INSTANT LOSS OF PWR AND ALT. STARTED EMER CHKLIST; BUT LOSING ALT TOO RAPIDLY TO CONTINUE CHKING THINGS OUT. HAD SET PLANE UP FOR 70 MPH GLIDE SPD. I DECIDED TO MAKE A PRECAUTIONARY LNDG STRAIGHT AHEAD TO A FARM FIELD RATHER THAN TRYING TO SOLVE A DETERIORATING PROB IN THE AIR. ONLY OTHER PROB -- HIGH VOLTAGE PWR LINE AHEAD. IMPOSSIBLE TO GAIN ALT TO GO OVER SO DECIDED TO LOWER NOSE AND GO UNDER; RAISING THE NOSE AND DIPPING THE TAIL JUST AS PASSING UNDER THE WIRES TO AVOID CATCHING THE TAIL ON THE WIRES. THIS RESULTED IN A FASTER THAN DESIRED TOUCHDOWN AND ROLLOUT ON A VERY UNEVEN; GRASSY FIELD. UPON COMING TO A STOP WE DETERMINED NO INJURY TO OURSELVES. GOT OUT AND CHKED PLANE AND FOUND NO INJURY TO GEAR; PROP OR ANY OTHER PARTS. CALLED ARPT ON RADIO AS TO WHAT HAPPENED AND MADE ARRANGEMENTS FOR ACFT TO BE TOWED OUT OF FIELD AND DOWN THE ROAD BACK TO THE ARPT. LANDOWNERS ARRIVED AND NOT UPSET. MECH WAS CALLED AND CAME TO SCENE; CHKED ACFT AND SUPERVISED TOWING. RUN-UP WAS DONE BY MECH AT THE ARPT AND FOUND THE R MAGNETO HAD FAILED. EXAMINATION OF MAGNETO AT SHOP REVEALED A SECTION OF 6-8 TEETH MISSING ON NYLON GEAR. SHAFT SPUN FREELY. NO EXPLANATION OF HOW IT COULD HAVE HAPPENED. LESSON AND ACTIONS TO BE LEARNED: EVEN WHEN RUN-UPS SEEM FINE IT IS NO GUARANTEE OF A TROUBLE FREE TKOF OR FLT. ALWAYS; ALWAYS STAY ALERT FOR SOMETHING TO HAPPEN AND HAVE A PLAN OF ACTION. AND REMEMBER THE INSTRUCTION TO FLY THE AIRPLANE FIRST AND LAND STRAIGHT AHEAD. IF I HAD TRIED A RETURN TO THE RWY THE RESULTS WOULD HAVE BEEN FATAL I'M SURE. AND ADD TO YOUR PRELNDG CHKLIST TO CHK OUT THE AREA PAST THE DEP END OF THE RWY AT EVERY ARPT FOR JUST SUCH AN EVENT WHEN YOU LEAVE. YOU CAN DO THIS AS YOU ARE APCHING THE ARPT. I HAD PRACTICED OFF ARPT LNDGS WITH MY INSTRUCTOR EVERY YR ON THE WINGS PROGRAM (NOW HAVE PHASE XI). IT CERTAINLY PAID OFF WHEN THE REAL THING HAPPENED. MAY IT NEVER HAPPEN AGAIN.