On October 5, 1997, a Hiller UH-12C (registration N49983) was involved in an aviation accident near Bennington, VT. Investigators recorded the probable cause as: The failure of the cyclic control due to an improper modification by the pilot/owner. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter rolled right and struck the ground after the cyclic stick detached from the pilot's controls during a hover demonstration. The stick had been modified by attaching a military-style cyclic via a repaired joint, but maintenance records did not indicate who performed the modification.
Incident Overview
A certificated flight instructor (CFI), who also owned the helicopter, was demonstrating hovering techniques to a student pilot. During the demonstration, the student pilot attempted to hover the helicopter, at which point the helicopter began to roll to the right. The CFI reached for his controls, but the top of the cyclic stick detached. Consequently, the helicopter continued to roll right and collided with the ground.
Examination Findings
Post-accident examination revealed that the cyclic stick had been replaced with a military-style cyclic. The owner reported that the stick had been cut down by removing a section, and the cyclic separated at the repaired joint. A review of maintenance records did not disclose who performed the modification or when it occurred.