SANTA ANA, CA, USA
N74520
MOONEY M20B
THE ENGINE ON A MOONEY M20B FAILED WHILE ON SHORT FINAL APPROACH. EXAMINATION REVEALED THAT THE BOLTS RETAINING THE IDLER SHAFT HAD SHEARED ALLOWING A CHANGE IN THE INTERNAL TIMING AND FAILURE TO DRIVE THE LEFT MAGNETO. BOTH BOLT HEADS, THE LOCKPLATE, AND THE COTTER KEYS WERE FOUND IN THE OIL SUMP. THE IGNITION SPRINGS ON THE ELECTRICAL HARNESS HAD EVIDENCE OF ARCING.
THE FAILURE OF BOLTS RETAINING THE IDLER SHAFT ALLOWING THE CAM SHIFT TIMING TO CHANGE AND BY ITS FAILURE TO DRIVE THE LEFT MAGNETO.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
