What happened
On 22 October 2004, a Reims Cessna F406 Caravan II, registration G-TWIG, was performing a routine freight delivery flight near Inverness. The aircraft was completing its fifth sector of the day, flying from Stornoway to Inverness. After climbing to Flight Level 95, the pilot requested a descent to Flight Level 75. During this descent, the aircraft's rate of descent became unstable, and it entered a steep, left-hand spiral dive. The aircraft struck the ground at high speed on a mountain ridge known as Meall Feith na Slataich, approximately 37 miles northwest of Inverness. The impact was so severe that the airframe was extensively fragmented. The pilot, the sole occupant of the aircraft, was killed in the crash.
The investigation
Investigators examined the wreckage and analyzed air traffic control recordings. The pilot had been communicating clearly and calmly with controllers until the final transmission, showing no signs of distress or emergency. Radar data showed the aircraft's descent rate became abnormal shortly before contact was lost. The investigation looked into several potential causes, including mechanical failure, environmental factors, and pilot incapacitation. While the wreckage was widely scattered, there was no evidence of major engine or airframe failure, nor any evidence of a collision with birds or other foreign objects. The investigation also considered the possibility of an electric trim runaway, noting that the elevator trim had moved to a near full nose-down position.
Findings
- The aircraft entered a sustained, high-speed spiral dive during a descent from FL95 to FL75.
- The pilot's last radio contact was calm and indicated no known difficulties.
- The exact cause of the sudden deviation from controlled flight could not be determined due to insufficient evidence.
- Potential contributing factors included sudden physical or mental incapacitation of the pilot, or an encounter with localized turbulence or windshear.
- There was no evidence of any attempt by the pilot to recover from the dive.
Safety action
- The AAIB reiterated recommendations for EASA to develop standards for inexpensive, lightweight flight data and voice recording equipment suitable for small aircraft.
- The investigation supported the promotion of cockpit voice recorders for all aircraft used in commercial air transport, regardless of their weight or age.