On November 14, 1986, a Hughes 369D (registration N1089D) was involved in an aviation accident near Winlock, WA. Investigators recorded the probable cause as: The pilot's failure to maintain adequate clearance between the long-line sling and the treetops, which resulted in the sling rebounding into the tail rotor and causing gearbox damage. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter sustained tail rotor gearbox damage after the long-line sling rebounded into the rotating blades while returning to a pickup area, leading to a hard autorotative landing.
What happened
The pilot was engaged in an aerial logging operation, specifically loading Christmas trees from a farm onto a truck. After releasing a load, the aircraft was en route back to the pickup area when the empty long-line sling made contact with the treetops below. The impact caused the sling to rebound upward, striking the tail rotor assembly and damaging the gearbox. This mechanical failure resulted in a loss of control. The pilot initiated an autorotative landing to manage the emergency, but the helicopter touched down hard.
The investigation
The primary mechanical issue identified was damage to the tail rotor gearbox caused by the rebounding long-line sling. No other mechanical failures were noted prior to the impact event.
Findings
Tail rotor gearbox damage sustained from contact with a rebounding sling
Loss of control following the mechanical failure
Hard landing during autorotation attempt
Probable cause
The pilot's failure to maintain adequate clearance between the long-line sling and the treetops, which resulted in the sling rebounding into the tail rotor and causing gearbox damage.