What happened
On 12 May 2012, a Pegasus Quik microlight, registration G-CWIK, was being flown on a private flight from Perth to Glenforsa. The aircraft was carrying the pilot and one passenger. While transiting the area, the aircraft was flying at approximately 6,000 ft above scattered cloud.
As the aircraft approached the summit of Ben More in Stirlingshire, it descended below the cloud base to roughly 100 ft above the mountain peak. Video footage recovered from the aircraft shows that the flight path remained stable until approximately 300 metres from the summit. At this point, the aircraft encountered intense turbulence in the lee of the mountain, causing it to roll rapidly and pitch nose-down. The engine speed increased significantly, suggesting the pilot was attempting to arrest a descent and climb out of the turbulent air. The aircraft subsequently struck the south-eastern side of the mountain, 100 ft below the summit. Both occupants sustained fatal injuries.
The investigation
The AAIB investigation utilized several sources of evidence, including wreckage examination, radar data, and footage from a GoPro camera attached to the aircraft. The examination of the wreckage found no evidence of mechanical failure or structural issues prior to the impact. The damage to the propeller and the state of the engine indicated that the engine was producing power at the time of the crash.
Radar data from NATS and secondary radar from a nearby helicopter helped reconstruct the flight path and confirmed that no other aircraft were involved in the accident. Meteorological analysis revealed that while surface winds were moderate, the wind speed at the summit was significantly higher due to the Venturi effect. A witness on the summit described very strong winds, which was consistent with the aircraft's track being downwind of the peak.
Findings
- The aircraft encountered severe turbulence created by the wind flowing over the summit of Ben More.
- The intensity of the turbulence in the lee of the mountain exceeded the safe operating limits for the microlight.
- A lack of awareness regarding the specific wind conditions and the severity of turbulence downwind of high ground contributed to the accident.
- The impact forces were far beyond human tolerance, making the accident unsurvivable.