On June 26, 1996, a Hughes 369D (registration N5125Q) operated by U.s. Forest Service was involved in an aviation accident near Ketchikan, AK. Investigators recorded the probable cause as: The pilot's failure to maintain clearance between the tail rotor and ground obstacles while the helicopter was at full operating RPM, resulting in a rock strike. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 8 related events involving the same aircraft type or operator are linked below.
A helicopter sustained significant structural damage after its tail rotor struck a rock while at full operating RPM during post-landing operations in a remote area.
What happened
The pilot landed the aircraft in a remote location to facilitate the transport of three U.S. Forest Service employees into a national forest. Upon landing, the employees exited the helicopter and began walking away from the aircraft.
While the helicopter remained at full operating RPM, it rocked backwards. This movement caused the tail rotor to strike a rock on the ground. The impact resulted in substantial damage to several critical components of the tail assembly.
The investigation
Examination of the aircraft revealed specific mechanical failures resulting from the tail rotor contact with the rock. The damage was extensive and affected multiple systems within the tail section.
Tail rotor blades sustained visible damage
The gearbox incurred structural harm
The tail boom showed signs of impact
The drive shaft was compromised
Probable cause
The pilot's failure to maintain clearance between the tail rotor and ground obstacles while the helicopter was at full operating RPM, resulting in a rock strike.