What happened
On June 5, 2014, a Piper PA-38-112 Tomahawk, registration HB-PGU, was conducting a training flight at the Grenchen Regional Aerodrome. The flight, intended for flight student instruction on grass runway operations, initially experienced a rejected takeoff attempt due to the pilot's assessment of an excessive angle of attack. Following this, a second takeoff attempt was initiated on grass runway 25L.
During the second departure, the aircraft accelerated but failed to gain sufficient altitude. The aircraft lifted off just before the end of the runway at a low airspeed. Despite attempts by the flight instructor to take control and increase speed, the aircraft was unable to climb out of ground effect and crossed a nearby road at a very low altitude. To avoid more significant obstacles, the instructor performed an emergency landing in a nearby field. During the impact, the left main landing gear was severed from the fuselage, and the aircraft sustained heavy damage, though the crew escaped without injury.
The investigation
SUST examined the aircraft's performance, weight, and mechanical condition. The investigation focused on why the aircraft was unable to maintain a climb after liftoff. Investigators reviewed the takeoff procedures being practiced, the aircraft's weight at the time of departure, and the engine's operational state. The investigation also reviewed the crew's decision-making regarding the takeoff roll and the management of the aircraft's pitch during the acceleration phase.
Findings
- The aircraft's takeoff mass was 808 kg, which exceeded the maximum allowable takeoff weight of 758 kg by 50 kg.
- The engine's performance was compromised due to fouled spark plugs, which placed the engine's output at the lower limit of its capability.
- The crew's method of monitoring acceleration progress was focused on a specific point in the middle of the runway, which led them to proceed with the takeoff despite insufficient acceleration later in the roll.
- The use of the elevator during the takeoff roll contributed to the performance issues.
- The aircraft lifted off at an insufficient speed to sustain a climb given the increased weight and reduced engine performance.