What happened
On 25 May 2005, a Slingsby T67C Firefly, registration G-FORS, was conducting a training flight near Potterspury, approximately 6 miles northwest of Milton Keynes. The flight was being conducted by an experienced instructor and a student with no prior flying experience. The aircraft departed from Turweston Aerodrome at 1545 hrs.
During the flight, the aircraft was observed by witnesses to be flying at a low altitude and low speed. The aircraft subsequently entered a spin, which witnesses described as a clockwise rotation. The aircraft continued to spin until it impacted a field containing wheat. The impact caused the destruction of the aircraft and resulted in 2 fatalities.
The investigation
The AAIB investigation examined the wreckage, radar data, and witness accounts. Radar tracking indicated the aircraft was at a minimum altitude of 2,000 ft agl before contact was lost. While there was no definitive evidence of mechanical failure, investigators looked into the possibility of engine issues or control obstructions. The engine was found to have been producing very little power at the time of impact, and the alternator warning light had illuminated, suggesting the engine might have been struggling or windmilling.
Investigators also reviewed the training syllabus. The student's logbook indicated that the instructor had been performing exercises involving oscillatory stalling. While this specific maneuver is not part of the standard UK Private Pilot’s Licence syllabus, it was a known practice for this instructor.
Findings
- The aircraft entered an unintentional spin during an exercise involving oscillatory stalling.
- The instructor was unable to recover the aircraft from the spin before it struck the ground.
- The aircraft was at its aft center of gravity limit, which may have contributed to the difficulty of recovery.
- The use of oscillatory stalling during early-stage training is considered inappropriate for ab initio students.
- There was no evidence of a mechanical failure that would have caused the spin, though a potential engine distraction or a loose article impeding controls could not be entirely ruled out.