Cessna 150 N7922E accident near Fayetteville, West Virginia

Probable cause

A loss of engine power due to the failure of the left magneto system’s distributor gear as a result of the improper maintenance of the magnetos by maintenance personnel.

NTSB analysis

The pilot stated that during the initial climb the airplane engine's rpm gauge indicated 1900 and the airplane would not gain altitude which resulted in a forced landing. Postaccident examination of the airplane revealed fuel in the fuel tanks and carburetor system. All cylinders had compression when checked. The right magneto developed sparks to all corresponding plugs. The left magneto produced spark to one plug only. A teardown examination of the left magneto revealed the distributor gear had 12 gear teeth sheared from the disk. Review of the engine's maintenance records showed that the ignition system had several inspections as required by airworthiness directives and service bulletins (SB) throughout its time in service. The distributor gear was required to be replaced with a redesigned gear as outlined in SB658; however, both magnetos had the old-style distributor gear, dating to before 1978. Additionally, the gear tooth separation was noted starting and ending at the magneto timing block location marker. The manufacturer of the magneto warned not to use a gear holding tool during installation, which may cause hidden damage to the distributor gear and subsequent engine failure.

Text from the NTSB. Open the NTSB docket for ERA10LA475 for the full record.