History of the Flight
The pilot of Flight Design CT2K G-CBUF, a microlight aircraft, departed Hunsdon, Hertfordshire, for a private photographic flight with a passenger. After receiving clearance from Stansted tower to enter the control zone below 1,000 ft QNH (approximately 750 ft agl), the pilot initiated a sustained 40° banked turn to the left. After about three orbits, the engine stopped suddenly. With limited height available, the pilot could only level the wings and prepare for a forced landing in a field of standing corn. The aircraft touched down and pitched over onto its back. The occupants were uninjured and exited through the doors.
Examination of the Aircraft
Returning the following day to recover the aircraft, the pilot found approximately 10 litres of fuel remaining in the right tank and evidence of slow fuel seepage during the inverted attitude. The flight duration was about one hour; based on a consumption of 12 litres/hour, the pilot estimated about 25 litres remained at the time of the accident, well above the three litres considered unusable. An examination by the manufacturer’s representative found no evidence of a mechanical problem; the most likely cause of the engine stoppage was considered fuel starvation.
Fuel System Design
The CT2K has fuel tanks in the inboard wing sections. UK-registered aircraft are fitted with a fuel selector that supplies fuel from either the left or right tank, but not both simultaneously, to comply with British Civil Airworthiness Requirements (BCAR) Section S. Non-UK registered CT2Ks and the later CTSW model allow simultaneous feed. The UK representative noted that this arrangement had led to several fuel starvation incidents.
In a left turn, fuel in the right tank may move outboard, away from the outlet located in the aft inboard region. The pilot commented that he chose a left turn to avoid uncovering the right tank outlet in a right turn. During an imbalanced turn, the fuel could shift, potentially uncovering the outlet.
Safety Recommendations
Two safety recommendations were issued: 2006-105 to the CAA to review BCAR Section S fuel system requirements for consistency, and 2006-106 to P&M Aviation, the UK agent, to consider modifying CT2K fuel systems to allow both-tank feed similar to the CTSW.
The CAA commented that regardless of tank selection, fuel flow should be uninterrupted under normal conditions, and questioned whether a “both” selection would have helped given one tank was nearly empty. The BMAA noted that the Section S working group was addressing the issue.