BO-105S N131EH accident near Thibodaux, Louisiana

Probable cause

The pilot's inability to maintain control due to the mechanic's inadvertent switching of two cyclic control tubes of different lengths during maintenance.

NTSB analysis

While in a 3-foot hover the helicopter began an uncommanded roll to the right. The pilot unsuccessfully attempted to arrest the roll by applying full left cyclic. Moments later the right landing skid made contact with the ground, followed by the main rotor blades. The helicopter came to rest in a right-side-low, upright position and the pilot was able to exit unassisted. The purpose of the flight was to perform an operational flight check of maintenance performed to the cyclic control system. The investigation revealed that the mechanic who had performed the maintenance had inadvertently switched two cyclic control tubes, of different lengths, during reassembly. This resulted in an out-of-rig condition in the cyclic control system. No other preimpact anomalies were noted with the helicopter's flight control system.

Text from the NTSB. Open the NTSB docket for CEN09LA571 for the full record.