On June 24, 1989, a Bell 47G-2 (registration N1161N) was involved in an aviation accident near Centralia, WA. Investigators recorded the probable cause as: THE PILOT MISJUDGED HIS CLEARANCE OVER TREES, WHICH RESULTED IN AN IN-FLIGHT TAIL ROTOR STRIKE WITH THE TREES AND LOSS OF TAIL ROTOR CONTROL. THE TREES WERE A RELATED FACTOR. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter lost tail rotor control after a loud pop during a turnaround maneuver over trees, impacting and rolling over during autorotation. Examination found torsional drive shaft failure but no preimpact part failure.
Incident Details
During aerial application operations, the pilot was performing a turnaround maneuver over trees between swath runs. While executing the turn, the pilot heard a loud 'pop' and subsequently lost tail rotor control. The helicopter began rotating, and the pilot initiated an autorotation. However, the helicopter impacted the ground while still rotating and then rolled over.
Examination Findings
An examination of the tail rotor drive system revealed damage to the tail rotor blades as well as torsional failure of the tail rotor drive shaft. No preimpact part failure was found in the examined components.