SEDONA, AZ, USA
N4113R
PIPER PA-32-300
THE PLT & 4 FARE-PAYING PAX WERE ENROUTE TO THE GRAND CANYON NATIONAL PARK FOR AERIAL SIGHTSEEING. AN INTERNAL FAILURE OF THE LEFT MAGNETO (MAG) RESULTED IN A TOTAL LOSS OF ENGINE PWR. THE ACFT COLLIDED WITH TERRAIN & WAS DESTROYED BY GROUND FIRE. THE MAG WAS SUBJECT TO AD 78-09-07 R3 WHICH ADDRESSED IMPULSE COUPLING FAILURE. UPON EXAM IT WAS NOT FOUND TO HAVE BEEN IN COMPLIANCE WITH THE AD. THE AIR TAXI COMPANY HAD TWO EMPLOYEES; AN OWNER/PRESIDENT/PILOT AND A DIRECTOR OF MAINTENANCE/MECHANIC. THE MECHANIC ACKNOWLEDEGED HE FAILED TO FOLLOW THE CURRECT GUIDELINE IN THE CORRECT AD. AS A RESULT, THE IMPULSE COUPLING JAMMED WHEN THE FLYWEIGHT TO STOP PIN CLEARANCE BECAME ZERO. THIS ACTION SHEARED OFF TEETH ON THE ENGINE'S CRANKSHAFT GEAR & DOWEL PIN.
TOTAL FAILURE OF THE MAGNETO'S IMPULSE COUPLING WHICH RESULTED IN A SHEARING OF THE CRANKSHAFT'S IDLER GEAR TEETH AND THE CRANKSHAFT DOWEL PIN.
Source: NTSB Aviation Accident Database
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