A recently published accident report from the U.K.’s Air Accidents Investigation Branch (AAIB) has confirmed previously released details by Vertical Aerospace on its August 2023 eVTOL accident.
According to the May 2 investigation report, the accident was caused by a failure of the adhesive bond between the propeller blade sheath and spar, causing a propeller blade to detach from an electric propulsion unit.
“Large out-of-balance loads generated by the blade release caused structural failure of the right inboard pylon, resulting in damage to the aircraft’s wiring harnesses,” the report stated.
This caused the aircraft to lose thrust from two motors, and while the aircraft was able to maintain a level attitude, the loss of vertical thrust resulted in “substantial damage” to the eVTOL when it hit the ground.
The Aug. 9, 2023, crash took place during the company’s flight program at Cotswold Airport — home to Vertical’s flight test center. The full-scale experimental prototype was remotely piloted at the time and there were no injuries during the accident.
“The manufacturer identified the propeller blade’s structural design, the manufacturing controls, quality assurance processes and verification programme as contributory factors to the blade failure,” the report stated.
Vertical claims that at the time of the accident, the company had already redesigned the early generation propeller that would eliminate the bonding failure that caused the blade release. Vertical said it is no longer using the first-generation propeller blades, and following its own internal accident investigation, the company said it has identified 36 product and process improvements that it intends to implement.
At the time of the accident, Vertical founder Stephen Fitzpatrick said that “while a fault of any sort is disappointing, it is not wholly unexpected at this stage of testing a novel aircraft.”
Vertical is currently completing the final assembly of its second full-scale VX4 prototype, telling shareholders in March 2024 that it expects to begin its flight test program with that second prototype ahead of its planned public demonstrations at Farnborough and Heathrow.
The second prototype will comprise 70% new components compared to the previous model, which includes the company’s “more advanced” propellers, as well as its proprietary battery technology.
“This aircraft will be faster and quieter than our first prototype, and is a big step forward toward certification,” Fitzpatrick told shareholders.
