What happened
Following a three-point landing, the pilot of the aircraft reported that a significant vibration or shimmy began emanating from the tailwheel area. Immediately after this vibration started, the airplane began pulling to the right. Despite the pilot applying corrective actions, the aircraft continued to track toward the right and exited the runway edge.
After leaving the runway, the aircraft collided with a berm and underwent a ground loop. The pilot was not injured in the event.
The investigation
A post-accident examination of the tailwheel assembly was conducted. This inspection revealed that the left control spring had become disconnected. The pilot indicated his belief that the shimmy occurring during the landing phase caused the spring to disconnect.