The commercial pilot was conducting a flight in the Zenith CH750 Cruzer 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.
He then made a forced landing in an open field in Louviers, Colorado. The airplane hit 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 post-accident 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.
NTSB Identification: CEN18LA042
This November 2017 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Don’t Need No Stinkin’ ECU!
Way too many pilots have absolutely NO IDEA of what is going in forward of the fire wall.
I’m no Internal combustion engine mechanic but I understand Suck, squeeze, bang , blow.
It doesn’t make them a bad person. They very likely know stuff about some other topic that I know NOTHING about.
But when your life depends on the big fan up front having power it really pays to have a better, at least BASIC understanding of what ‘s going on under the cowl.
In addition to your comments, how many folks know anything about their car engines and what to do when the ECU detects a fault ?
Do they know about the OBD2 connector and that using a scanner, it will display the fault.
Most repairs are usually fairly simple to do.
The only experimental engine that has demonstrated reliability is the Rotax 900 series.
An experimental engine in an experimental aircraft doubles the risk of problems.
From the docket, the engine had coolant in 3 of the cylinders, so my thoughts are that the overheating warped the head the allowed coolant into the engine and caused it to stop. The viking engine has had a number of cooling/ blown head gasket issues.
My preference is to use a Continental or Lycoming engine so that I’ll know that the engine will be reliable.
Auto engine conversions won’t be as reliable as a certified aircraft engine, with their psru and the idea that auto engines spend most of their life running at 15-20% power vs aircraft needing 60-75% power.
I’ll take a mixture control and a good EDM any day.
Given that you can lean anywhere relative to peak below 60-65% power and not harm the engine, I wonder why the pilot didn’t notice the overheat condition, reduce the power accordingly and land at the nearest airport?
Having the automation of engine control doesn’t eliminate the operator’s understanding of the internal combustion process. That’s the problem with automation dependency in all areas of mechanical operation in today’s world and dependency in general. Understanding the basics is always a good thing.