Report: Structural Failure of Cagatay CGT-50 at Radnor Range

Incident overview At 11.15am on 5 October 2023, a Cagatay CGT-50 unmanned aircraft was conducting a demonstration flight at Radnor Range, Powys. Weighed to its maximum takeoff weight of 55kg, the aircraft took off vertically and transitioned into a forward climb. Around 12 seconds later, at an altitude of 235ft, the right wing bent upwards at the root and detached. The aircraft descended rapidly, tumbling to the ground at about 60mph and coming to rest more than 100m away from pyrotechnic operatives who had been standing directly under the flight path. There were no injuries.

Structural failures and production errors An investigation by the Air Accidents Investigation Branch (AAIB) concluded that the wing assembly on the accident aircraft did not have sufficient structural strength to carry the bending loads encountered in 1 g straight and level flight. The primary cause of the failure was the use of wing joiners – cylindrical carbon fibre tubes that act as wing spars – that were significantly shorter than the design specification. The forward joiner measured 226cm, whereas the required length was 2.48m. The operator’s internal investigation determined that old stock wing joiners from a previous product, the CGT-45, were likely inadvertently fitted at the production facility in Turkey.

The structural weakness was exacerbated by an asymmetric installation of the wing joiners. A missing end cap in the left wing’s joiner guide tube, combined with an absence of assembly procedures instructing technicians to centralise the joiners on the fuselage, allowed the forward joiner to be biased towards the right wing. This created an uneven bending load distribution.

Detailed component examinations also revealed poor manufacturing quality. The glass fibre reinforced polymer (GFRP) root rib reinforcement exhibited a lack of surface preparation and a poor adhesive bond to the wing root skin, which promoted peeling fractures under wing bending loads.

Operational context and hazard management The flight was operating in the specific category under a Civil Aviation Authority (CAA) operational authorisation. The aircraft was not required to be built or tested to any recognised safety standards; instead, the safety case relied heavily on operational procedures to separate hazards from uninvolved persons.

The demonstration was originally scheduled for 1pm but was brought forward because of a favourable weather window. As a result, pyrotechnic operatives were still present in the operating area. Although the flight team called for takeoff permission over the radio, unclear communications with the range and a lack of direct radio contact with the pyrotechnic operatives severely reduced situational awareness.

Safety actions In response to the incident, the operator implemented several measures to improve component control and manufacturing quality. These included introducing dimensional tolerances and individual serial numbers for wing joiners, performing quality control checks upon receipt of components, and modifying the aircraft design to use standard supplied joiner lengths without the need for shortening. The joiner guide end caps were also redesigned to increase their adhesive surface area.

The range subsequently reviewed its safety plan. It stated its intention to ensure robust radio communications, mandate that the location of every person on the range is accounted for before takeoff, and introduce standard phraseology, including a ‘stop stop stop’ call for anyone identifying a hazard

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