WPR18LA004

The pilot and mechanic reported that, before the accident, the mechanic had adjusted the helicopter’s main rotor track and balance. After the mechanic made the final adjustments, the pilot hovered the helicopter to a wash rack for cleaning. Subsequently, while the pilot was repositioning the helicopter to a nearby landing cart and just as the front portions of the skids were over the cart, the collective began to oscillate, followed by the skids striking the cart. The pilot attempted to land the helicopter as it continued to oscillate, but the right skid slid off the cart. The helicopter then rolled onto its right side and impacted the ground. The mechanic reported that all components prior to the accident were in good working order and that the track and balance adjustments had resulted in satisfactory monitoring equipment readings prior to the accident. Examination of the helicopter did not reveal evidence of any preaccident malfunctions or failures that would have precluded normal operation. The reason for the oscillations could not be determined based on the available information.

On October 13, 2017, about 1015 Pacific standard time, a Williams Helicopter Corporation UH-1H helicopter, N247PV, was substantially damaged when it was involved in an accident near Arbuckle, California. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 repositioning flight. The pilot and mechanic reported that, before the accident, the mechanic had adjusted the main rotor track and balance. After the mechanic made the final adjustments, the pilot hovered the helicopter to a wash rack for cleaning. Subsequently, while the pilot was repositioning the helicopter to a nearby landing cart, the collective began an uncommanded surge up and down just as the front portion of the landing skids were over the cart. The skids struck the cart causing damage to the front tips. The pilot attempted to land the helicopter on the cart as the collective continued to oscillate. The right skid slid off the cart and the helicopter rolled onto its right side and impacted the ground. The mechanic reported that all components prior to the accident were in good working order and that the track and balance adjustments had resulted in satisfactory monitoring equipment readings prior to the accident. Examination of the helicopter revealed that the airframe was substantially damaged, and that the main transmission, tail rotor, and right horizontal stabilizer had fracture separated. The pitch change links were all bent, and the main rotor blades were destroyed. Examination of the helicopter did not reveal evidence of any preaccident mechanical malfunctions or failures that would have precluded normal operation. The pilot did not submit a National Transportation Safety Board Pilot/Operator Aircraft Accident Report Form 6120.1.