What happened
On February 17, 2021, a Tecnam P2008 JC, registration HB-KML, was performing a training flight at Biel-Kappelen (LSZP) under Visual Flight Rules. The aircraft, operated by Swiss Aircrafts AG, was being piloted by a flight instructor accompanied by a student.
Prior to the flight, the instructor noted that the grass runway surface was soft and slippery due to a freeze-thaw cycle overnight. During taxiing, the aircraft's nosewheel became stuck in the soft grass, requiring assistance from another instructor to move the plane onto the runway. Despite these indications of high rolling resistance, the instructor decided to proceed with the takeoff based on anecdotal information that a similar situation had occurred the previous day without issue.
During the takeoff roll on runway 23, the pilot observed that acceleration was significantly lower than normal. At the point where a road crosses the runway, the indicated airspeed was only 45 knots, whereas the aircraft would typically be airborne by that stage. Attempting to reach the required rotation speed of 50 knots, the pilot continued the roll, but the aircraft failed to accelerate further. The pilot then initiated an aborted takeoff, applying brakes intermittently to prevent the wheels from locking on the wet surface. Consequently, the aircraft overran the end of the runway and came to a stop in an adjacent field approximately 130 meters beyond the runway threshold. There were no injuries to the two occupants, and the aircraft sustained no damage.
The investigation
The SUST investigation examined the runway conditions, the aircraft's performance, and the pilot's decision-making process. The investigation established that the aircraft's weight was 580 kg, well within the maximum allowable limit of 650 kg. While the engine produced the expected power, the soft, saturated state of the grass significantly increased rolling resistance. The investigation also reviewed the pilot's reliance on outdated information regarding the runway's condition from the previous day, which did not reflect the current state of the surface.
Findings
- The primary cause of the incident was that the takeoff roll was continued despite recognized low acceleration, leading to a late decision to abort.
- The soft and saturated grass runway significantly increased the required takeoff distance beyond standard calculations.
- The pilot's decision-making was influenced by misleading information that the runway conditions were similar to the previous day, which was not accurate.
- The pilot lacked a pre-established, clear criterion for when to initiate an immediate takeoff abort during the roll.