What happened
On August 10, 2007, a Maule M-5-235C seaplane, registration OH-MAI, capsized on the border of Leppävesi and Laukaa, Finland. The aircraft, operated by Keski-Suomen Ilmailijat ry, was attempting to take off from a calm water surface.
The pilot attempted three separate takeoffs. During the first two attempts, the aircraft failed to reach takeoff speed and failed to rotate properly. The pilot noted that the aircraft's nose did not rise to the expected angle. Following the second attempt, the pilot decided to abort the flight and return to the departure pier. While taxiing back, the pilot executed a left turn. During this maneuver, the aircraft tilted sharply to the right, the right float tip submerged, and the aircraft capsized. The pilot and passenger were able to escape onto the floats and were rescued by passing boats.
The investigation
The investigation focused on why the aircraft became unstable during the taxiing maneuver. Investigators examined the condition of the floats, the aircraft's configuration, and the pilot's technique.
It was established that the aircraft's floats were in poor condition and had been subject to leaks. Specifically, the maintenance access covers were not properly sealing due to worn or incompatible screws and mounting hardware. During the taxiing and the failed takeoff attempts, water entered the floats through these insufficient seals. Additionally, the investigation found that the aircraft's elevator trim was set forward of the takeoff position, and the flaps were incorrectly configured during the first attempt. The aircraft also lacked a valid weighing certificate for the float equipment.
Findings
- Water ingress into the floats was the primary cause of the accident. The accumulation of water significantly increased the aircraft's mass and shifted the center of gravity forward beyond the allowable limit.
- The improper takeoff technique and high engine RPM during taxiing caused the floats to sit deeper in the water, facilitating the ingress of water through the faulty access covers.
- The pilot's limited experience with seaplane operations in calm water conditions contributed to the failure to recognize the developing instability.
- The aircraft's configuration, including incorrect trim and flap settings, contributed to the failed takeoff attempts and the increased duration of the taxiing period.
- The lack of use of checklists resulted in the pilot overlooking critical configuration checks, such as the position of the trim, flaps, and water rudder.