What happened
On 7 February 2019, a pilot employed by the manufacturer was conducting a demonstration flight using an Evolve Dynamics Sky Mantis unmanned aerial system (UAS) at Nailsea Fire Station, Somerset. The aircraft, which was operating at its maximum takeoff mass, had initially taken off with a 100% battery charge and a voltage of 25.2 V.
After reaching an altitude of approximately 50 m, the UAS maintained a steady hover for about five minutes. However, as the pilot attempted to rotate the aircraft on its yaw axis, the four electric motors ceased operation simultaneously. This sudden loss of power occurred without any prior warnings appearing on the controller, and the aircraft became unresponsive to all pilot inputs. The UAS began a rapid descent, entering autorotation at an altitude of roughly 10 to 15 m. The descent could not be arrested, resulting in a hard impact with the ground. The onboard battery subsequently ignited, causing the aircraft to be destroyed.
The investigation
The manufacturer conducted an internal investigation into the sudden loss of propulsion. The inquiry established that the electrical connection to the battery had been interrupted during flight. It was determined that the battery had not been properly secured in its housing prior to takeoff.
Findings
- The primary cause of the power failure was that the battery was not fully locked in place.
- Vibrations during flight caused the battery to lose contact with the electrical terminals, leading to the total loss of motor power.