What happened
On 15 September 2007, a Eurocopter AS350B2 helicopter, registration G-CBHL, crashed in a heavily wooded valley near Lanark, Scotland. The flight was a private operation, and the pilot was returning to a home helipad after a short trip to a nearby farm.
During the return leg, witnesses observed the aircraft flying at a high speed and a low altitude. The helicopter was seen performing a sharp right turn before banking steeply to the left and descending into the Mouse Water valley. The aircraft struck trees in the valley, causing the main rotor blade to detach and the tail boom to separate. A severe post-crash fire destroyed much of the cabin structure. There were four fatalities in total, including the pilot and three passengers.
The investigation
The AAIB investigation examined the wreckage, radar data, and witness accounts. Evidence from the impact site showed the aircraft struck a fir tree with a level trajectory, suggesting the helicopter was intact and the engine was producing power at the moment of impact. The investigation also reviewed the pilot's licensing history, noting that the pilot's flying licence and type rating had expired.
Meteorological data indicated brisk to strong winds in the area, with some turbulence. While no specific technical failure was confirmed, investigators considered the possibility of a 'servo transparency' phenomenon, which can cause uncommanded movements during certain manoeuvres.
Findings
- The helicopter struck trees while performing a high-speed, low-altitude manoeuvre.
- The pilot was attempting a demanding turn in a heavily wooded area, which likely led to a deviation from the intended flight path.
- The pilot's flying licence and type rating were invalid at the time of the accident.
- Environmental factors, including a strong tailwind and the complexity of the terrain, contributed to the difficulty of the manoeuvre.