Pilot Debrief

MOTLEY GARY W ZENITH CH750 CRUZER near Louviers, CO — 2017-11-27

Final reportCEN18LA042
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Date
2017-11-27
Location
Louviers, CO, USA
Aircraft
MOTLEY GARY W ZENITH CH750 CRUZER
Registration
N956GM
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Climb

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.

NTSB narrative

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.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have aborted the flight after ECU installation if engine issues were evident.

NTSB coding

Evidence available

  • Photos
  • 3 docket documents
View NTSB final reportView NTSB docket

Docket documents3

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