Kaman Aerospace Corp K-1200 N134WC accident near Donnelly, Idaho

Probable cause

The collision of two counter-rotating main rotor blades for undetermined reasons, which resulted in a loss of control.

NTSB analysis

While lifting a heavy external load off the ground, the leading edges of two of the logging helicopter's counter-rotating main rotor blades collided with each other. The collision resulted in the destruction of a significant portion of both of those blades and the separation of one of the two main rotor pylons. Control of the helicopter was no longer possible, and it impacted the terrain in the inverted position. Detailed postaccident examinations of the helicopter’s components, tests, and witness interviews did not reveal evidence of any pre-existing anomalies or malfunctions or of any pilot action that would have led to the blades colliding. Although the helicopter was operating at an estimated 288 pounds above its maximum certified gross weight of 12,000 pounds, there is no evidence that this played a role in causing or contributing to the blade-to-blade contact. The event that initiated the accident sequence was not determined.

Text from the NTSB. Open the NTSB docket for WPR10FA295 for the full record.