What happened
On 30 January 2022, a Kolb Twinstar Mk III (registration G-MZZT) was performing a private flight from a grass runway near St Albans. Shortly after departing Runway 30, the aircraft veered sharply to the right and struggled to gain altitude. The aircraft flew at a very low altitude, passing near a hangar, farm buildings, and power cables.
As the aircraft reached approximately 100 ft agl, the engine ceased operation. The aircraft then descended steeply and struck the ground in a fallow field between runways. The pilot, who was the sole occupant, sustained minor injuries but was able to exit the wreckage without assistance. The aircraft was destroyed in the impact.
The investigation
The AAIB examined the wreckage and the engine to determine the cause of the flight instability and the engine failure. While the pilot initially reported a control restriction, investigators found no mechanical evidence of such a blockage in the control cables or rods. However, they noted several loose items within the cockpit area that could potentially obstruct controls.
Regarding the engine, a borescope inspection of the Rotax 582 engine revealed heavy scoring and evidence of overheating in the rear cylinder. Investigators also found that the propeller pitch had been adjusted to a lower setting than recommended by the manufacturer to achieve higher engine RPMs during ground testing. Additionally, the investigation noted several maintenance concerns, including improper electrical wiring, an undersized engine mounting bolt, and the use of non-standard sealant in the gearbox.