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ASN Wikibase Occurrence # 218695
Last updated: 2 December 2021
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Type:Silhouette image of generic CH75 model; specific model in this crash may look slightly different
Zenith CH 750 Cruzer
Registration: N956GM
MSN: C75-10359
Fatalities:Fatalities: 0 / Occupants: 1
Other fatalities:0
Aircraft damage: Substantial
Location:Louviers, CO -   United States of America
Phase: Unknown
Departure airport:Broomfield, CO (BJC)
Destination airport:Broomfield, CO (BJC)
Investigating agency: NTSB
The commercial pilot was conducting a flight in an experimental airplane to assess engine performance after installing a replacement engine control unit (ECU) with updated programming. During the flight, the engine monitor provided an alert regarding a high engine coolant temperature. Shortly afterward, the engine seized. The pilot attempted two engine restarts, including a complete reboot of the ECU, without success. The pilot made a forced landing in an open field. The airplane struck a barbed wire fence, causing damage to the nose landing gear, engine cowling, right wing strut, and right wing skin. Also, the pilot noticed that the coolant expansion tank had overfilled due to overheating.
A postaccident examination revealed that the ECU had caused the engine fuel-air mixture to be too lean, resulting in excessive cylinder head temperatures, which caused the engine to seize. The excessive cylinder head temperatures also resulted in the unseating of the head gasket, which pressurized the coolant jacket and evacuated engine coolant overboard. Coolant was found in three of the four cylinders, and oil was mixed in the coolant under the thermostat, resulting in the rapid rise of coolant temperature.

Probable Cause: The engine’s excessive cylinder head temperatures and the subsequent seizing of the engine, which resulted from an engine control unit that caused the engine’s fuel-air mixture to be too lean.



Accident investigation:
Investigating agency: NTSB
Status: Investigation completed
Duration: 1 year
Download report: Final report

Revision history:

28-Nov-2018 14:46 ASN Update Bot Added

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