What happened
On August 24, 2009, at approximately 17:15, a towing operation at Räyskälä aerodrome resulted in a significant accident involving a Piper PA-25-235 Pawnee (registration OH-PDW) and a Rollanden-Schneider LS 1-f glider (registration OH-959).
During the takeoff roll on runway 30, the glider experienced several bounces and drifted slightly to the side. Once airborne, the glider's upward movement increased significantly, causing its nose to pitch up and the aircraft to climb well above the level of the tug. The tension on the tow rope pulled the tail of the Piper PA-25-235 Pawnee sharply upward. Before either pilot could release the tow rope, the release mechanism on the glider side failed, causing the rope to break at an altitude of approximately 110 meters.
Following the separation, the tug aircraft entered a steep dive toward the ground. The pilot managed to recover the aircraft's attitude just moments before impact. The Piper PA-25-235 Pawnee struck the ground belly-first, causing the landing gear to collapse and the propeller blades to bend. The aircraft slid approximately 20 meters across a grassy area. The pilot of the tug sustained minor injuries, including a head injury caused by striking the door handle after the seatbelts detached from their mounting wires during the impact. The glider, meanwhile, completed a normal landing on the grass.
The investigation
The investigation examined flight data recorders from both aircraft, which recorded altitude and ground speed. Investigators analyzed the aircraft's configuration, specifically the placement of the tow release mechanism, and the experience levels of both pilots. The investigation also reviewed the structural integrity of the seatbelt mounting in the tug aircraft.
Findings
- The primary cause of the accident was the glider climbing too high during the tow, which forced the tug's nose into a sharp downward pitch.
- The glider's tendency to pitch up was exacerbated by the position of the tow release mechanism, located in front of the landing gear, which creates an upward force.
- The pilot of the tug had not trimmed the aircraft sufficiently nose-down to counteract this upward pull.
- A delay in releasing the tow rope by either pilot allowed the tension to reach a point where the glider's release mechanism broke.
- The pilot of the glider was performing his first flight in this specific aircraft type.
- The seatbelt mounting wires in the tug aircraft failed under the impact loads, which is a concern noted in previous investigations.