Silence Twister, G-TWST
The newly built aircraft was on a local test flight when the engine started to run roughly and reduce in power so the pilot made a precautionary landing at Aylesbury airfield. After inspecting the engine and carrying out power checks the problem cleared so he departed again. The aircraft climbed to approximately 400 feet agl before the engine started to run roughly again. As there was insufficient runway remaining to land straight ahead, he elected to carry out a short circuit. On the downwind leg the engine ceased producing all power so he landed in a field causing the gear to collapse. The pilot was able to exit unassisted. An examination of the aircraft revealed resin particles in the fuel system that could have restricted or blocked the fuel flow. The manufacturing process of the fibreglass fuel tanks was not ensuring adequate removal of all wax releasing agent from inside the tank. When the ribs were bonded to the tank using the resin, some resin was bonding inadequately to residual wax deposits inside the tank. The pilot had flushed his tanks out using water but when the tanks were subsequently filled with fuel, the fuel probably helped to remove the poorly bonded resin from the wax, leaving the resin free to enter the fuel lines. The manufacturing process has since been improved and the build manual has been revised to include instructions to clean the fuel tanks with fuel.
Published 10 December 2014