What happened
Following takeoff, the pilot experienced an audible "pop" from the engine, which was immediately followed by a total loss of engine power. This failure necessitated a forced landing into a group of trees.
The investigation
Investigators examined the engine and discovered that a recently installed, factory remanufactured single-drive dual magneto had separated from the engine. At the time of the accident, this component had accumulated only 17.9 hours of use.
Detailed examination of the magneto and the installed clamping blocks revealed fatigue beach marks on the mounting flanges on both sides of the distributor housing. The investigation identified two distinct sets of contact marks on these flanges:
- An inboard set of smaller, more linear marks that matched the contour of the installed clamping blocks.
- A second, wider set of marks with curved ends that did not correspond to any feature of the installed older-style clamping blocks.
A small step was observed at the edge of the larger contact area, suggesting the displacement or removal of material from the flange surface. These larger marks matched the configuration and shape of newer-style clamping blocks introduced by the engine manufacturer for engines produced after March 1985.
While the engine manufacturer had introduced these newer blocks as a production improvement, their use was not mandatory for the engine installed in this aircraft. Additionally, the magneto manufacturer noted that during the remanufacturing process, housings are stripped of paint and dipped in a dichromate bath for corrosion prevention; while these components underwent inspection for cracks, the process was limited to a visual examination.