LAX90LA066

1990-01-06 · SANTA ANA, California, United States · Minor · 1 aircraft · Status: Completed

Airport SNA

Aircraft involved

N74520 Mooney M20B Minor

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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