What happened
On May 9, 2008, a Beechcraft 35-C33, registration HB-EHB, was conducting a technical test flight near the Neuchâtel airfield in Switzerland. The flight, which included a pilot and a mechanic, was intended to verify the performance of a newly installed engine. After a normal takeoff, the crew began reducing power during the climb. At this stage, the mechanic noticed a drop in fuel flow and, suspecting a mechanical pump failure, activated the electric auxiliary fuel pump.
As the aircraft approached runway 23 for a return to the airfield, the pilot found the aircraft too high and too fast for a landing. Despite deploying the landing gear and flaps, the aircraft passed the midpoint of the runway. The pilot attempted a go-around; however, during this maneuver, the aircraft lost sufficient power to climb. The aircraft subsequently performed a low-altitude turn, struck tree branches, and impacted a field. The left wing hit the ground first, and the aircraft came to rest approximately 30 meters from the initial impact point. Both occupants escaped the wreckage without injury, and no fire occurred.
The investigation
Investigators examined the engine, the cockpit controls, and the flight sequence. The engine was tested on a test bench and found to be in good working order, with no installation defects or mechanical failures identified. The investigation focused on the cockpit configuration, noting that the three engine control levers—throttle, propeller, and mixture—were all the same color but had different shapes and were arranged in a specific layout.
Findings
- The primary cause of the accident was a loss of control resulting from a chain of incorrect manipulations.
- The reduction in fuel flow was not caused by a mechanical failure but by the pilot accidentally pulling the mixture lever instead of the throttle lever.
- The activation of the auxiliary fuel pump by the mechanic did not resolve the issue because the fuel supply was being restricted by the incorrect mixture setting.
- The pilot's approach to runway 23 was late and poorly configured, as the aircraft was too high and too fast for a safe landing.
- During the go-around, the pilot failed to retract the flaps, which, combined with the engine power deficit caused by the mixture setting, prevented the aircraft from gaining necessary altitude.