What happened
On 5 March 2000, a Jodel D112, registration G-BHHX, was returning to Dunkeswell after visiting a private airstrip in the Mendip hills. While cruising at approximately 1,500 feet, the pilot and passenger were suddenly subjected to intense airframe vibrations. This was accompanied by significant fore and aft movement of both control sticks.
In an attempt to mitigate the shaking, the pilot reduced the aircraft's airspeed, which lessened the intensity of the vibration, though the movement remained very pronounced. The occupants held the control sticks firmly to try and dampen the motion. The pilot notified Dunkeswell air traffic control of the situation and declared an intention to perform a precautionary landing in a field at Kingston-St-Mary. A nearby YAK 52 aircraft observed the Jodel from above and later confirmed to controllers that the aircraft had completed a successful landing in the grass field.
The investigation
Following the landing, an inspection of the aircraft's control surfaces was conducted. The investigation established that the elevator trim tab cable had broken at the connection point to the tab input arm. This mechanical failure caused the trim tab to flutter, which in turn induced a flutter-displacement of the elevator itself.
To facilitate the aircraft's departure from the field, the trim tab was removed from the elevator. The aircraft was subsequently able to fly back to Dunkeswell without further incident.