SEA94LA030

The pilot heard loud grinding sounds from the rear of the aircraft, followed by banging sounds and a loss of directional control. He jettisoned his logs, then his long line, and executed a powered autorotation into the trees, substantially damaging the aircraft. The 42 degree intermediate gearbox was examined and multiple origin fatigue cracks were found in fragments of the input pinion gear.

On November 12, 1993, at 1130 Pacific standard time, a Hawkins and Powers UH-1B, N91NW, operated by Northwest Helicopters, impacted terrain 10 miles south of North Bend, Washington, during an emergency forced landing. There was no flight plan filed for the external load flight, conducted under 14 CFR 133 in visual meteorological conditions, that was on takeoff when the accident occurred. The commercial certificated pilot suffered minor injuries in the accident. The aircraft was substantially damaged. There was no fire.

The pilot reported he heard a loud growling/grinding noise from the rear of the aircraft, followed by a slow turn to the right, then a banging sound and a violent rotation to the right. After clearing the choker setters with the load, he jettisoned his external load of logs and attempted to fly the aircraft to a nearby clearcut. Recognizing that he had neither altitude nor airspeed to make it to the clearcut, he reduced power, jettisoned his long line, and executed a powered autorotation into the trees. The aircraft was substantially damaged when it impacted the trees and rough terrain.

The 42 degree intermediate gearbox was examined at the NTSB metallurgy laboratory. Fatigue cracks and overstress fractures were found in the input geat and mating fragments.