A report stated that an electrically powered aircraft had to perform a forced landing after its battery was disconnected as part of a flight testing.
Modified Piper PA-46-350P was undergoing "experimental" testing when it "suffered from a loss in power to the electric motors", according to the Air Accidents Investigation Branch, (AAIB).
It had to land at Cranfield Airport, Bedfordshire, on the 29th of April 2021.
According to the AAIB, the aircraft suffered "severe damage" during landing.
This plane was built as part of an experimental program to develop aircraft propulsion systems that emit less noise and produce zero emissions.
Two electrical motors were installed to replace the piston engine. They are powered by a high voltage lithium (HV), and a hydrogen fuel cells (HFC) battery.
The report stated that the battery was turned off as part of the testing procedure with the intent of leaving the electric motors powered solely by the hydrogen fuel cells.
"During the interruption, the windmilling propeller of the aircraft generated enough voltage to power the inverter protection device.
"This caused the motors to stop working and pilot and observer couldn't reset the system to restore power."
Pilot responded by saying "the voltage is too high" when power was lost. The report stated that the pilot had to respond quickly.
Forced landing was performed and the aircraft touched down on a field. It passed through a hedge as the left wing gave way.
According to the report, both pilot and observer were not injured.
The accident was caused by a variety of factors, including an ineffective emergency procedure and insufficient ground testing. It also revealed that the risk assessment for the two flights in which propulsion was lost on the previous flights had not been reviewed.
According to the report, the experiment team had a heavy workload and was under pressure to complete a long-lasting demonstration flight by May 2021.
"The operator's investigation revealed that certain staff showed signs of pressure to make decisions based on expediency." The report stated.
Following its report, the AAIB provided five safety recommendations to the Civil Aviation Authority regarding the project and the aircraft.
The operator took a variety of safety measures to address the findings of the report, including managing "commercial pressure" so that safety was not compromised.
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