Pilot Debrief

ZENITH CH701 near Bothell, WA — 2022-07-20

Final reportWPR22LA263
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Date
2022-07-20
Location
Bothell, WA, USA
Airport
PAE
Aircraft
ZENITH CH701
Registration
N8787G
Category
Airplane
Highest injury
Serious
Fatalities
0
Phase of flight
Descent

Probable cause

A loss of engine power due to the fatigue failure of the engine’s flywheel screws that were likely overloaded when the engine was involved in a previous accident.

NTSB narrative

The pilot reported the takeoff and en route portions of the flight were uneventful. While descending to the traffic pattern altitude at the destination airport, the engine lost power and the propeller stopped. The pilot made an emergency landing on a vacant road, colliding with powerlines. A postaccident examination of the engine revealed that the flywheel screws had separated due to fatigue, resulting in an engine failure. Examination of the screws showed multiple fatigue cracks and wear consistent with low-stress bending fatigue. Maintenance records revealed that the engine had been installed in another airplane that was involved in an accident where the propeller was damaged. According to the engine manufacturer, abrupt propeller stoppage can produce a spike of torque along the crankshaft, overloading the flywheel screws and causing failure. There was no evidence that the screws were replaced after that accident.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Proper maintenance of flywheel screws could have prevented engine power loss.

NTSB coding

Evidence available

  • 6 docket documents
View NTSB final reportView NTSB docket

Docket documents6

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