What happened
During a scheduled flight test of the G-HYZA, an aircraft utilizing a hydrogen fuel cell (HFC) and a high voltage (HV) battery, the crew experienced a sudden loss of propulsion. The flight was intended to test the ability of the HFC to maintain electrical power alone after the HV battery was deactivated during the downwind leg of the circuit.
After taking off from Runway 03, the pilot climbed to 1,000 ft agl. While flying the downwind leg, the crew adjusted power and propeller settings to assess performance. As the aircraft approached the runway threshold at approximately 940 ft agl, the pilot reduced power to 90 kW and switched the HV battery to the off position. At this moment, all electrical drive to the propeller ceased.
The crew attempted several system resets and tried to reconnect the HV battery, but electrical power could not be restored. As the aircraft descended to 320 ft aal, the observer noted critically high voltage levels. Realizing they lacked the altitude to complete a standard landing maneuver, the pilot declared a MAYDAY and prepared for a forced landing in a nearby field.
The aircraft type touched down on a level grass field at approximately 87 kt. During the landing roll, the aircraft struck a hedge, causing the left wing to separate, and the landing gear entered a ditch, bringing the aircraft to a halt. There were 0 fatalities and 0 injuries among the crew.
Findings
- The loss of propulsion occurred immediately upon the deactivation of the HV battery, indicating the HFC failed to provide sufficient electrical power to the motors.
- The crew attempted to restore power through multiple reset procedures and by re-engaging the HV battery, but these efforts were unsuccessful.
- The flight test parameters were being flown at power and airspeed settings that differed from the original flight test card.