What happened
On 5 October 2023, a Cagatable CGT-50 was conducting a demonstration flight at Radnor Range, Powys. The aircraft, a vertical takeoff and landing (VTOL) unmanned system, was performing a scheduled flight as part of a week-long technology event. After taking off vertically and transitioning into a forward climb, the aircraft reached a speed of approximately 53 KTAS. During steady, 1 g straight and level flight, the right wing began to bend upwards at the root before completely detaching from the fuselage. The remaining portion of the aircraft entered a rapid, uncontrolled tumble and struck the ground near pyrotechnic operatives who were working in the area. The impact resulted in the destruction of the aircraft.
The investigation
The AAIB examined the wreckage and identified significant structural failures within the wing assembly. Investigators found that the wing joiners—the cylindrical carbon fibre tubes acting as spars—had fractured due to static overload. Measurements revealed that the joiners installed in the accident aircraft were shorter than the required design specification. Specifically, the forward joiner was found to be 2.0 cm longer than the standard, but the installation was asymmetrical, causing an uneven distribution of bending loads.
Further examination of the wing root rib revealed poor surface preparation and inadequate adhesive bonding between the composite layers. The investigation also noted that the wing design allowed for movement in the joiner position and that assembly instructions lacked requirements to ensure the joiners were centered symmetrically within the fuselage. The investigation also looked into the proximity of personnel, noting that a change in the flight schedule had placed pyrotechnic workers under the flight path at the time of the accident.
Findings
- The wing assembly lacked the necessary structural strength to withstand standard bending loads encountered during level flight.
- The use of undersized wing joiners from an earlier aircraft model created an uneven load distribution on the forward wing joiner.
- The wing design permitted the joiner position to shift, which, combined with a lack of symmetrical installation procedures, contributed to the failure.
- Poor manufacturing quality, including inadequate surface preparation and bonding at the wing root rib, compromised the structural integrity of the attachment point.
- A schedule change brought the flight forward, resulting in personnel being positioned within the flight path during the accident.