NTSB CAROL · Event
Event LAX90LA066
Aircraft involved
Probable cause & findings
THE FAILURE OF BOLTS RETAINING THE IDLER SHAFT ALLOWING THE CAM SHIFT TIMING TO CHANGE AND BY ITS FAILURE TO DRIVE THE LEFT MAGNETO.
Factual narrative
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. Source: NTSB Aviation Accident Database (Pre-2008 Archive) Retrieved: 2026-02-12
Verbatim from NTSB's published report. Source file
NTSB_1990_LAX90LA066.txt.
Findings + structured fields enriched from FAA avall.mdb.
Full investigation docket on
data.ntsb.gov ↗.
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