What happened
On 12 May 2000, a Slingsby T61F Venture T Mk 2, registration G-BUFP, was performing an instructional flight from Dunstable Downs Airfield. The aircraft was utilizing the 'north east run', a takeoff direction characterized by an initial uphill climb followed by a downhill section.
During the takeoff roll, the aircraft experienced several bounces on the grass surface. As the aircraft approached the airfield boundary, it became airborne but was at a very low altitude. The aircraft struck the upper branches of a large tree located near the airfield's entrance road. This impact caused the left wing to be largely destroyed, forcing the aircraft into a nose-down, inverted, and yawed attitude. The aircraft then struck the B 489 road in a near-vertical manner before sliding across the tarmac. A fire broke out in the engine area following the impact, and both the instructor and student sustained serious injuries.
The investigation
Investigators examined the wreckage and the engine, which had been overhauled only 50 hours prior to the accident. The examination of the engine and its components revealed no mechanical failures or power reductions that could have contributed to the accident. All flight control surfaces and systems were found to be in working order and properly connected.
Environmental and operational factors were also scrutinized. The investigation noted that light rain had occurred shortly before takeoff. While the instructor believed the aircraft was lighter than a previous flight, the takeoff run was conducted on mown grass that varied in length, with taller grass present toward the end of the run. Furthermore, local topography and wind conditions were noted to potentially cause sink or turbulence immediately after departure.
Findings
- The aircraft's failure to achieve a safe takeoff altitude was caused by the adverse combination of moisture on the wings, the length of the grass on the takeoff run, and the prevailing wind conditions.
- Moisture on the wings can significantly degrade takeoff performance, potentially doubling the required runway length and impairing the initial climb.
- The aircraft struck a tree at a low altitude, leading to the subsequent impact with the road and the resulting fire.