What happened
On 11 May 2011, a Piper PA-25-235 Pawnee, registration G-BSTH, was performing glider aero-tows at Portmoak Airfield in Kinross. The pilot had successfully completed six previous tow operations that day, reaching altitudes of 2,500 ft despite some turbulence. During the seventh tow, the aircraft encountered rain at approximately 2,000 ft.
Due to the difficulty of seeing through a windscreen covered in rainwater, the pilot decided to terminate the tow and land immediately. The pilot successfully released the glider from the cable. However, as the aircraft turned onto final approach, the combination of a low sun position and the rain-affected windscreen significantly restricted the pilot's vision.
While flying a crabbed approach to compensate for a left-hand crosswind, the aircraft drifted right of the centerline. The aircraft stalled at a height of roughly 5 ft and impacted rough ground to the right of the prepared runway strip. The impact was severe enough to cause the landing gear shock struts to fail. The pilot shut down the engine and safely exited the aircraft without injury.
The investigation
The investigation was based on the aircraft accident report form provided by the pilot. Investigators examined the circumstances surrounding the visibility issues and the aircraft's flight path during the final approach. The investigation established that the pilot had previously operated in similar conditions, but the specific combination of environmental factors on this occasion led to the loss of visual clarity.