What happened
On 21 August 2014, a Kolb Twinstar MKIII (registration G-MYPC) was performing circuit training near Shifnal Airfield in Shropshire. The pilot, who had recently completed a run-in period for a newly installed crankshaft, was executing approaches to Runway 18. After climbing to approximately 500 feet and retracting the flaps, the pilot reduced power to cruise RPM. At this stage, a loud, rough noise emerged from the engine area, accompanied by intense vibrations throughout the airframe.
Faced with the necessity of an immediate landing and constrained by overhead power cables, the pilot selected a nearby field for a forced landing. During the landing roll, the aircraft's speed was too high to avoid a wooden fence at the edge of the field. An attempt to climb over the obstacle failed, resulting in the main landing gear striking the fence before the aircraft came to rest in a hedge. There were no injuries to the pilot.
The investigation
The investigation examined the mechanical condition of the engine and propeller following the impact. The aircraft sustained significant damage to the wings, landing gear, propeller, and the fuselage pod and boom. Post-accident inspections of the propeller revealed that two of the three blades had sustained damage, including tip delamination and a missing section of a blade tip. Additionally, a portion of the starter motor mounting flange was found to be missing.
Findings
- The primary cause of the incident was severe engine or propeller vibration encountered during the climb.
- The damage to the propeller blades may have been the source of the vibration, though it was unclear if this damage occurred during flight or upon impact.
- The pilot's landing options were restricted by the presence of several sets of power cables in the vicinity of the airfield.