What happened
On 10 June 2006, a Flight Design CT2K, registration G-CBUF, was conducting a private photographic flight near Sawbridgeworth, Hertfordshire. After departing Hunsdon and receiving clearance to enter the Stansted Control Zone, the pilot maintained a height of approximately 750 ft agl. During the flight, the pilot entered a sustained, 40-degree banked left turn consisting of several orbits.
While performing these continuous left turns, the engine stopped suddenly. Due to the low altitude, the pilot had very little time to react before the aircraft impacted a field of standing corn. The impact caused the aircraft to pitch over onto its back. Despite the impact, the two occupants sustained no injuries and were able to exit the aircraft through the doors.
The investigation
Investigators examined the aircraft's fuel system and noted that the UK-registered Flight Design CT2K was equipped with a fuel selector that allowed the engine to be fed from either the left or right tank, but not both simultaneously. Prior to the flight, the pilot had noted a significant fuel imbalance, with the left tank nearly empty and the right tank containing approximately 40 litres.
An examination of the aircraft following the accident revealed approximately 10 litres of fuel remaining in the right tank, along with evidence of a slow fuel seepage that had occurred while the aircraft was inverted. The investigation focused on whether the fuel movement during the steep left turn caused the fuel outlet to become uncovered.
Findings
- The engine stoppage was caused by fuel starvation.
- During the sustained left turn, the aircraft's lateral weight distribution and centrifugal forces likely caused the fuel in the right tank to move outboard, away from the fuel outlet.
- The fuel system design on UK-registered Flight Design CT2K aircraft prevented the engine from drawing fuel from both tanks at once, which could have mitigated the imbalance.
Safety action
- The AAIB made a safety recommendation to the CAA to review the Section S Fuel System design requirements to ensure consistent application of regulations to UK-registered aircraft.
- A recommendation was also made to the manufacturer's UK agent to review the fuel system design to ensure reliable fuel flow under all operating conditions.