As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT MAG DROPPED TO ZERO ON RUN UP THE AIRCRAFT WAS SENT TO AIRCRAFT MAINTENANCE WE PULLED THE LEFT MAGNETO P/N 4371 S/N 10081489 AND FOUND ONE SIDE OF THE IMPULSE COUPLING PAWL WAS SHEARED OFF AND HAD JAMMED UNDER SIDE, THE INSIDE OF THE MAGNETO WAS DESTROYED AND METAL WAS FOUND. WE COMPLIED WITH LYCOMING SB 480F CORRECTIVE ACTION 3. THE OIL PAN WAS REMOVED AND CLEANED THE OIL FILTER WAS REPLACED AND SCREEN CLEANED. PART TOTAL TIME UNKNOWN 286.6 HRS SINCE A 500HR INSPECTION