Air Accidents Investigation Branch
The aircraft was being flown by a remote pilot on a test flight at 30 ft agl when a propeller blade detached from the electric propulsion unit 3 forward motor due to a failure of the adhesive bond between the propeller blade sheath and spar. Large out-of-balance loads generated by the blade release caused structural failure of the right inboard pylon, resulting in damage to the aircrafts wiring harnesses. This caused a loss of thrust from motors 4 and 7. Whilst the aircrafts flight control system was able to maintain a level attitude, the high rate of descent caused by the loss of vertical thrust resulted in substantial damage to the aircraft when it struck the ground.
The aircraft manufacturer was, at the time of the accident, in the process of introducing a blade design that, amongst other things, eliminated the bonding failure mode that caused the blade release. The manufacturers investigation identified 36 product and process improvements resulting from findings of the investigation.