What happened
On July 14, 2007, at approximately 14:30 local time, a Fournier RF 4 Mod engine glider, registration OH-381X, was involved in an accident during a takeoff attempt at Nummela Aerodrome (EFNU), Finland. The pilot intended to conduct a local flight to the west of the aerodrome.
Upon beginning the takeoff roll on the gravel runway 27, the aircraft experienced several intermittent liftoffs, or "bouncing," before reaching the required rotation speed. As the aircraft continued down the runway, the pilot observed that the airspeed was not accelerating sufficiently to maintain flight. After passing the threshold of runway 22, the pilot decided to abort the takeoff while the aircraft was airborne at an altitude of a few meters.
During the aborted takeoff, the pilot applied the wheel brakes but did not use the aerodynamic brakes. The aircraft struck the runway surface with significant force, causing the pilot to sustain injuries and resulting in extensive damage to the aircraft, including the propeller, carburetor, engine cowling, landing gear, and wing structure. The aircraft eventually came to a stop on its nose.
The investigation
The investigation examined the pilot's recent flying experience, the condition of the aircraft, and the state of the aerodrome. It was established that the pilot had not flown this specific aircraft type for approximately seven months prior to the accident. While the pilot held valid licenses, the investigation noted that the pilot had not reviewed the aircraft's flight manual before the flight.
Investigators also assessed the runway conditions. Runway 27 was a gravel surface and was noted to be uneven. The investigation found that the lack of threshold and edge markings may have affected the pilot's assessment of the remaining runway length. Additionally, the investigation noted that the regulatory framework for aerodrome maintenance (AGA M1-2) was partially outdated.
Findings
- The primary cause of the accident was that the pilot failed to abort the takeoff in a timely manner despite the aircraft bouncing repeatedly during the takeoff roll.
- Contributing factors included the pilot's lack of recent experience with the Fournier RF 4 Mod.
- The uneven surface of the gravel runway likely contributed to the aircraft's instability and bouncing during the takeoff roll.
- The pilot performed the takeoff with the tailwheel off the ground, a technique that may have exacerbated the instability on the uneven surface.