Western International Avia Inc UH 1H N247PV accident near Arbuckle, California

Probable cause

A collective control malfunction for reasons that could not be determined.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for WPR18LA004 for the full record.