What happened
On 16 November 2007, a Kolb Twinstar Mk3 (registration G-BTYA) was conducting a private flight near Kilke and County Down, Northern Ireland. Approximately 10 to 15 minutes after departing, the pilot observed the left exhaust gas temperature gauge dropping toward zero.
Upon realizing the engine had failed, the pilot transferred control of the aircraft to the passenger, who possessed greater recent flying experience. The pilot directed the aircraft toward the airfield and notified the passenger. The aircraft flew toward the airfield for roughly 15 seconds before the crew attempted a forced landing in a large field identified as being free of livestock.
While the glide toward the field was initially successful, the aircraft encountered a localized area of sinking air approximately 20 to 30 feet above the field boundary. This sudden loss of lift caused the aircraft to strike a hedgerow situated on a raised bank, which contained a barbed wire fence. Both the pilot and the passenger sustained minor injuries.
The investigation
Investigators examined the aircraft following its removal from the accident site. An inspection of the engine revealed that it was free to rotate and contained a sufficient quantity of fuel. Subsequent testing by the pilot, after being discharged from the hospital, demonstrated that the engine could be started and operated without any detectable faults.
Meteorological data from the Met Office, including radiosonde ascent data from earlier that day, was analyzed. The data indicated a south-westerly flow with temperatures and humidity levels consistent with conditions where carburettor icing could occur.
Findings
- The engine failure was likely caused by the accumulation of ice within the carburettor.
- Meteorological analysis confirmed conditions that presented a possibility of serious icing at any power setting.
- The aircraft struck a hedgerow containing a barbed wire fence due to an encounter with sinking air during the final stages of the forced landing.