A Cozy Mk IV made an emergency landing on 18 March 2025 at Gloucestershire Airport (UK), leaving the pilot in light condition with some injuries.
During the final approach, the pilot applied power to stabilize the descent, but the engine did not respond. Within seconds, the plane completely lost power and ended up landing short of the runway, hitting and destroying the system’s antenna. Instrument landing system (ILS), a navigation aid that allows aircraft to line up on the runway and descend with precision, even in fog, heavy rain or very low visibility.
Up to that point, the facts pointed to another light aviation accident. However, a few months later the event was investigated by the Air Accident Investigation Branch (AAIB), the UK’s official body responsible for investigating aviation accidents and incidents. AAIB has just published its official report: The cause of the engine failure was not a conventional mechanical failure, but the collapse of a 3D printed part. installed in the intake system.
The Cozy Mk IV is a well-known amateur-built model airplane Between the private drivers and the component involved was an intake elbow responsible for channeling air to the engine.
Based on the official design of the Cozy Mk IV, This part must be manufactured with sheets of fiberglass reinforced with epoxy resin and must incorporate an aluminum tube at the inlet to resist high temperatures and vibrations in the engine compartment. But the part found after the accident was 3D printed in plastic and did not include the expected metal reinforcement. The owner bought it at an airfield in the United States, convinced that it was made of CF-ABS, a material supposed to withstand more than 100°C.
The AAIB carried out thermal tests on the material of the damaged part. The measurements revealed that the glass transition temperature, the point at which plastic begins to soften, was approximately 53°C. This value is much lower than typical temperatures inside the engine compartment during flight.. According to the official report, the component softened in mid-flight, lost its rigidity, became deformed and eventually collapsed on itself, blocking the engine’s air intake. Without enough air, the mixture could not be maintained and the engine completely lost power.
This Cozy Mk IV operated under the regime of Light Aircraft Association (LAA), which requires any significant modification to the fuel or intake system to be declared and evaluated by designated engineers. The investigation revealed that this 3D printed intake elbow was never included in the modification documentation presented, therefore, having not been declared, it was not evaluated nor subjected to the thermal or structural checks which would have detected that it was not suitable for installation on an aircraft.
The AAIB emphasizes that, if properly documented, the part would not have been approved.
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