Accident Overview
On 9 August 2023 at 0715 UTC, an experimental test flight of VA-1X, registration G-EVTL, ended with a hard landing at Cotswold Airport (Kemble), Gloucestershire. The aircraft, an eight-motor electric vertical takeoff and landing (eVTOL) prototype, was being flown remotely at 30 ft above ground level when a propeller blade detached from the forward electric propulsion unit (EPU) 3. The blade release resulted from a failure of the adhesive bond between the propeller blade sheath and spar. Subsequent out-of-balance loads caused structural failure of the right inboard pylon (pylon 3), damaging wiring harnesses and leading to a loss of thrust from motors 4 and 7. The flight control system maintained a level attitude, but the high rate of descent caused substantial damage upon ground impact.
History of the Flight
The aircraft was in its second test phase, having completed initial tethered flights. The accident flight was the twenty-second of the programme, intended to assess one-engine-inoperative performance during out-of-ground-effect hover. After routine checks, the aircraft lifted off vertically at 0714:25 hrs with all EPUs idling. The remote pilot shut down EPU1 per the test card, then climbed to 30 ft and accelerated to approximately 2-4 kt ground speed. At 0715:47 hrs, a loud 'pop' was heard as a propeller blade released from EPU3. The resulting imbalance caused pylon 3 to fail. Despite EPU1 restarting automatically, the aircraft could not maintain height and struck the ground three seconds later with a vertical descent rate of 19.45 ft/sec. There were no injuries and no third-party damage.
Aircraft Information
G-EVTL is an eVTOL prototype with a carbon fibre composite structure, fixed tricycle landing gear, V-tail, and high wing. For this test, its maximum takeoff mass was 3,737 kg. It could be flown with a pilot onboard or remotely. The aircraft had eight EPUs: four forward (driving five-bladed fixed-pitch propellers with tilt mechanisms) and four rear (fixed vertical, four-bladed). The forward propeller blades comprised an external sheath adhesively bonded to a carbon fibre spar. The propulsion system was powered by lithium-ion battery subpacks.
Accident Site and Examination
The aircraft struck the southern edge of Runway 26 in a level attitude, with the right mainwheel on pavement and left mainwheel and nosewheel on grass. The right wing failed at the inboard pylon but remained attached by wiring. The released blade sheath came to rest 50 m from the aircraft. Examination found that the blade sheath showed poor bonding: most adhesive remained on the internal sheath surface with little on the blade spar. Pylon 3 failed in overload due to high out-of-balance loads. Wiring damage included severed CAN bus wires and open circuits, leading to loss of thrust from motors 4 and 7.
Operator Response
The operator activated its emergency response plan. Airport fire services monitored the aircraft with a thermal camera; no fire occurred. A remote pilot and a high-voltage-trained technician shut down the electrical systems. The high voltage system was disconnected, and an insulation fault was isolated. Battery voltages and temperatures remained normal over three hours, allowing recovery.
Aerodrome Information
Testing was conducted at Cotswold Airport with special safety arrangements, including a sterile area. The aircraft and released blade remained well within this area throughout the flight and accident.