What happened
On 6 May 2017, a Zenair CH70 1UL, registration G-CBMW, was conducting a private flight from Rossall Field Airfield in Lancashire. Shortly after departing the airfield, while the aircraft was at an altitude of approximately 200 ft agl, the pilot noticed a reduction in engine power.
In response to the power loss, the pilot initiated a 90-degree turn to attempt a forced landing into the wind. However, the pilot identified obstructions on the ground directly ahead. As the aircraft continued the turn toward the reciprocal runway, the engine ceased functioning entirely at an altitude of 100 ft agl. The aircraft was unable to reach the runway and instead came down in an unprepared area adjacent to the airfield. Upon touchdown, the nose landing gear collapsed, causing damage to the propeller, engine cowlings, and the left wing. There were no injuries to the pilot.
The investigation
The investigation focused on the sudden loss of engine power and the mechanical state of the fuel system. The pilot reported that the aircraft had recently been fitted with new wing-mounted fuel tanks. The investigation established that the engine power loss was caused by the formation of an air lock within the fuel lines. This air lock, stemming from the recent installation of the new tanks, restricted the flow of fuel to the engine. It was determined that the risk of such an air lock occurring had not been identified during the installation or the subsequent inspection of the new fuel system.