Motley Gary W ZENITH CH750 CRUZER N956GM

Summary

On 27 November 2017 at about 22:20 local time, a Motley Gary W ZENITH CH750 CRUZER registered N956GM was involved in an accident near Louviers, Colorado, United States. One person was on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

27 November 2017 at 22:20

Classification

Accident

Location

Louviers, Colorado, United States

Coordinates

39.4622, -105.0078

Aircraft

Motley Gary W ZENITH CH750 CRUZER

Registration

N956GM

Category

Airplane

Year built

2017

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Flight Test

Phase of flight

Not recorded

Route

Broomfield → Broomfield

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN18LA042

Nobody was injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full 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.

Quoted verbatim from the NTSB record.