What happened
On August 27, 2019, a privately owned Scheibe SF-25C Falke was conducting a ferry flight from Kohnan Aerodrome in Okayama Prefecture to Makabe Gliderport in Ibarki Prefecture. During the flight, the pilot encountered inclement weather and low fuel, prompting a decision to land for refueling. While attempting to locate Okazaki Gliderport, the pilot misidentified a wide riverbed along the Yahagi River in Nishio-city, Aichi Prefecture, as the intended destination and landed there to use portable gasoline cans.
Following the refueling, the pilot attempted a takeoff from the riverbed. During the takeoff roll, the aircraft's heading deflected to the left, causing the left wing and left outrigger to become entangled in dense, tall grass. The aircraft subsequently fell approximately 3 meters from the riverbed level. The impact resulted in damage to the main wings and propellers, though the pilot and passenger escaped without injury.
The investigation
The Japan Transport Safety Board (JTSB) examined the aircraft's performance capabilities, the environmental conditions at the site, and the pilot's flight planning. The investigation focused on the available takeoff distance on the riverbed, the impact of the recent rain on the aircraft's aerodynamics, and the total weight of the aircraft at the time of the accident. Investigators also reviewed the flight manual's warnings regarding "wet wings" and the specific takeoff requirements for the aircraft type.
Findings
- The aircraft's weight at the time of the accident was approximately 589 kg, which exceeded the maximum takeoff weight of 580 kg.
- The pilot did not verify the surface conditions of the riverbed or calculate the necessary takeoff distance required for the current weight and environmental conditions.
- Because it was raining, the aircraft's wings were wet, which the flight manual notes can reduce lift and necessitate a higher takeoff speed.
- The available clear takeoff distance on the riverbed was approximately 135 meters, which was insufficient given the increased drag from the wet ground and the reduced lift from the wet wings.
- The flight plan was unrealistic, as the estimated duration exceeded the aircraft's actual fuel endurance under the planned cruising speed.
- The aircraft failed to accelerate sufficiently within the available riverbed length, leading to the collision with tall grass.