What happened
On 12 August 2009, a Flight Design CTSW, registration G-VINH, was conducting a private flight from Barrow-on-Furness to Kinloss. During the flight, the pilot climbed to various altitudes, reaching a peak of approximately 9,935 ft. While crossing the Firth of Tay, the pilot observed that the right wing fuel tank was empty and only 10 litres remained in the left tank.
Realising there was insufficient fuel to reach the destination, the pilot turned south toward Dundee Airport. Shortly before the engine lost power, the pilot noted that the left tank contained approximately 5 litres of fuel. The engine subsequently failed, and the pilot attempted a forced landing. After evaluating nearby areas, the pilot determined that playing fields were occupied by children and that the adjacent golf course fairways were too congested. Consequently, the pilot opted to land in a tree. The impact resulted in the aircraft destroyed and the pilot sustained minor injuries.
The investigation
The AAIB examined the wreckage and recovered a GPS unit and a multi-function display. Data from the GPS confirmed the flight path and altitude changes. Investigation of the engine components showed no evidence of pre-impact failure or lubrication issues, and the cylinders were in good condition.
Testing of the fuel tank was conducted to understand the fuel delivery. While the manufacturer's documentation suggested a very low unusable fuel quantity, tests performed with the aircraft in a nose-down attitude and a sideslip revealed that the unusable fuel could increase significantly. The investigation also noted that the aircraft's fuel tank design and the position of the sight tubes made accurate fuel gauging difficult during non-level flight.
Findings
- The engine became starved of fuel due to the low remaining quantity in the left tank.
- Flight planning was a contributing factor, as the pilot's estimated fuel consumption was lower than the actual consumption experienced during the flight, which included higher power settings and headwinds.
- The aircraft's fuel tank geometry and the position of the off-take tube meant that changes in aircraft attitude, such as sideslip or a nose-down pitch, could lead to the fuel feed being interrupted.
- The pilot's assessment of the remaining fuel was likely influenced by the difficulty of accurately reading the fuel sight tubes during flight.