ABOVE: Vertical Aerospace welcomes the report into the G-EVTL incident, strongly believing that ‘transparency and openness are fundamental to the safety of aerospace’

The Air Accidents Investigation Branch (AAIB) has released its investigation report into Vertical Aerospace’s flight test incident last August, highlighting that the primary cause of the crash was due to an adhesive bond failure of the eVTOL (electric vertical takeoff and landing craft)’s propeller blade.

At the time of the incident, the prototype VA-1X eVTOL was being flown remotely within a ‘sterile area’ of Gloucestershire’s Kemble airport on a flight test, the 22nd flight of the programme. The purpose of this specific test was to assess the impact of one engine inoperative performance during an out-of-ground-effect hover. However, with the aircraft stable at 30ft agl, a loud ‘pop’ was heard and a propellor blade became detached from electric propulsion unit (EPU) 3. The resulting ‘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,’ explains Vertical, with the eVTOL losing vertical thrust.

Despite the onboard flight control software being able to maintain a level attitude, the aircraft lost altitude and struck the ground at approximately twice the velocity it was designed for. Upon impact, the nose landing gear collapsed and the right wing sustained significant damage, remaining attached only through the wiring harnesses.

The failure of pylon 3 following the propeller blade’s release

Although Vertical was already in the process of introducing second-generation propellor blades at the time of the incident, the manufacturer has since identified 36 product and process improvements from its own internal investigation.

However, the incident does highlight further areas for consideration regarding emergency responses for battery-powered craft, especially as eVTOL manufacturers such as Vertical move closer to type certification and intended entry into service. In this instance, rescue and firefighting services at the airfield (having confirmed no fire was present) ‘monitored the aircraft with a thermal camera in order to detect any overheating of the aircraft’s batteries’, with a high-voltage trained “hook man” required to approach the aircraft and shut down its electrical systems. Battery back voltages and temperatures were then monitored over an immediate three-hour period before recovery could proceed.

The construction of Vertical’s second prototype aircraft – using upgraded parts and new suppliers – is currently moving closer to completion, with upcoming demonstration flights scheduled to take place at this year’s Farnborough airshow.