What happened
On 18 March 2025, a Cozy Mk IV, registration G-BYLZ, was performing a private flight at Gloucestershire Airport. After an uneventful local flight, the pilot was executing a Required Navigation Performance approach to Runway 09, intending to perform a go-around. During the final approach, the pilot deployed the belly airbrake. At approximately 500 feet, an attempt to advance the throttle resulted in a complete loss of engine power. The pilot managed to steer the aircraft away from a road and airfield boundary bushes, but the aircraft landed short of the runway and collided with the ILS localiser antenna array. The pilot sustained one minor injury, but the aircraft was destroyed.
The investigation
The AAIB investigation focused on the engine' and the fuel system, which had undergone a modification to include a mechanical fuel injection system. Investigators discovered that a 3D-printed plastic air induction elbow, part of this modified system, had collapsed. This collapse restricted the airflow required for the engine to function.
Further examination revealed that while the aircraft's original design called for a laminated glassfibre and epoxy resin elbow with an aluminium support tube, this 3D-printed version lacked the structural aluminium component. Although the owner believed the 3D-printed material (CF-ABS) had a high heat resistance, laboratory testing of the component showed a glass transition temperature of only approximately 53°C, significantly lower than expected. Additionally, the investigation found that the 3D-printed elbow was not listed on the parts list submitted to the Light Aircraft Association (LAA) during the modification approval process, meaning its airworthiness was never independently verified.
Findings
- The engine lost power because the 3D-printed air induction elbow softened and collapsed due to heat exposure.
- The 3D-printed material used was unsuitable for the high-temperature environment within the engine cowling.
- The lack of an aluminium reinforcement tube left the component structurally vulnerable.
- The modification approval process failed to catch the component because it was omitted from the official parts list provided to the LAA.