What happened
On August 19, 2015, a Sikorsky S-61A helicopter, registration N1043T, was performing a Part 133 firefighting flight near Ironside, Oregon. The flight, operated by Croman Corp, began at Baker City Municipal Airport (BKE).
While performing a climbing left turn approximately 20 feet above the ground after picking up 4,000 pounds of water, the aircraft experienced a power loss and a drop in RPM in the No. 2 (right) engine. The pilot dumped the water from the bucket and attempted to gain altitude and airspeed while entering a small valley. During the maneuver, the pilot attempted to release the longline, but the equipment failed to fully release from the helicopter fuselage.
Despite the second pilot using the emergency throttle, the engine and rotor RPM continued to decline. As the terrain rose, the pilot identified the flattest available spot and began slowing the aircraft. Before the helicopter touched down, the bucket struck trees and brush and became entangled in a wire fence. The helicopter landed as level as possible but subsequently rolled onto its right side. The accident resulted in 1 minor injury and 0 fatalities.
The investigation
An examination of the longline revealed that while the fuselage hook released the line as intended, one of the two hydraulic quick-disconnect (QD) couplings failed to release. Investigators found that a safety wire used on the fitting prevented the mechanism from functioning correctly.
Engine inspections focused on the No. 2 engine. While the No. 1 engine functioned normally during testing, the No. 2 engine showed metal debris on all four magnetic plugs. Investigators found wear marks on the radial driveshaft and the pinion gear assembly, indicating gear disengagement. Specifically, the pinion and bevel gears showed excessive wear and metal smutting at the tooth tips.
Further disassembly of the pinion support assembly revealed damage to the upper support bearing, including damage to the roller balls, bearing cage, and race. Notably, investigators found aluminum oxide particles embedded in the bearing components. Because aluminum oxide is not a component of the engine's lubrication system, its presence indicated it was likely introduced as an abrasive contaminant during the engine's overhaul or repair process.