Forced Landing of the First Hydrogen Fuel Cell Powered Test Aircraft
A hydrogen and batteries driven aircraft was forced to land after a flight incident. According to the aircraft company the aircraft was forced to an emergency landing, but landed normally on its wheels in a flat grass field and almost came to a stop, but was damaged as it caught the left main gear and wing in the uneven terrain at the end of the field at low speed.According to the sources, the flight conformed to the approved test route over the airport, and that the aircraft structural integrity was maintained throughout the incident sequence. The plan was to reach an altitude of 1,000 ft (305 m) with both the battery and fuel cell active, then switch the plane to fuel cell only, and fly three or more circuits. But as soon as the battery was switched off, the plane lost all drive to the propeller, and after several unsuccessful system reset attempts, the pilot made a forced landing. There were no unintended hydrogen or electrical releases and no fire. After the landing, the crew were able to safeguard the battery and safely release hydrogen from the on-board tanks. No fluid leaks were observed at the time and full data logs were preserved for use in an investigation.
Event Date
April 29, 2021
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The immediate cause was due to an expected sequence of events when performing airborne tests. When the battery system was switched off and power to the propeller was cut, the airflow through the propeller begun to drive it, causing the electric motors to begin acting as generators. The same situation had already occurred on two previous occasions, without the need of a forced landing; the first time prompted ZeroAvia to install a fault clear button, which was used successfully the second time power was lost. Thinking the problem was solved, the team continued the tests, but were caught out at the higher airspeed.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Fuel cell piper, on-board batteries, hydrogen storage
Storage/Process Medium
Location Type
Location description
Airport and/or Airborne
Pre-event Summary
The aircraft flew its first successful test flight in September 2020, completing taxi, take-off, a full pattern circuit, and landing. The test which caused Th incident, had already been performed in several previous flights, including one earlier that day, but at slower airspeeds. As ZeroAvia expanded the flight envelope to test higher speeds, the voltage generated by the free-wheeling propeller increased to a point where it triggered the overvoltage protection on the inverter, shutting the system down.
Currency
Lessons Learned
Lessons Learned
The result of the investigation is summarised in the reference. This event was related to a airplane prototype, and occurred when testing it. It served the manufacturer to improve the design and develop better operative and emergency procedures.
Event Nature
Emergency Action
Unknown
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Print out of the NEW ATLAS webnews of 3 May 2021 reporting the investigation results
https://newatlas.com/aircraft/zeroavia-hydrogen-crash-investigation-rep…