History of Flight
On January 8, 2010, about 1220 mountain standard time, a Hughes 369D helicopter, registration N500LW, experienced a loss of engine power and landed hard in the wilderness near Kooskia, Idaho. The helicopter was being operated by Quicksilver Air, Inc., under contract to the Idaho Department of Fish and Game for a wolf capturing mission. The pilot and two passengers sustained serious injuries; the helicopter sustained substantial damage. The flight originated from a ranger station about 25 minutes prior to the accident. Visual meteorological conditions prevailed, and no flight plan was filed.
According to passenger statements, the helicopter was maneuvering near the intersection of Kelly Creek and Moose Creek when several wolves were spotted. As the pilot maneuvered closer, a loud "bang" emitted from the engine compartment, followed by a loss of engine power and slight vibration. The rugged terrain was densely populated with trees. With the low rotor rpm light illuminated, the pilot attempted to fly toward an opening and the helicopter landed hard on ice.
The pilot reported that prior to the accident, he was maneuvering in a hover about 300 to 400 feet above the ground. He heard a "bang," immediately followed by the nose yawing to the left and the engine out light illuminating. He lowered the collective and entered an autorotation. He also reported a transient chip light illumination for several seconds about one hour prior to the accident. He performed a check on the enunciator panel at that time; all lights were operational, and no other lights illuminated until the loss of power.
Aircraft Information
The Hughes 369D, serial number 470120D, was manufactured in 1977 and had accrued about 13,197 total hours. The owner procured the helicopter in April 2005. The last airframe inspection occurred on December 31, 2009, about 30 flight hours prior to the accident. The helicopter was equipped with a Rolls-Royce 250-C20B turboshaft engine, serial number CAE-833319, rated at 420 shaft horsepower. The engine had accumulated 7,241.9 hours and had undergone a gearbox repair in October 2009, with reinstallation on November 2, 2009. The engine's compressor assembly, part number 6890550, had accumulated 301.9 hours since overhaul and was installed in June 2009. During the overhaul, a new No. 2 bearing (P/N 6889093AL, S/N TA 36-0510763) was installed, which was believed to be on the helicopter at the time of the accident. The operator stated no welding or high-energy maintenance had been performed on the helicopter, and it was not used for hot line powerline work.
Examination
Postaccident examination revealed substantial damage to the fuselage, particularly on the left side. The flight control system showed no evidence of mechanical malfunction or failure. No burn marks, arcing, pitting, or signs of high-temperature stress associated with electrical arcing were detected on the fuselage or airframe components.
Engine examination found crush damage to the combustor case. Rotational continuity was established for the N2 gear train, which rotated freely. Heavy binding was felt during attempted rotation of the N1 gear train. Engine chip detectors contained many metal particles. Disassembly revealed that the No. 2 bearing was fractured; the ball bearing retainer was separated in two locations, and numerous balls were gouged and deformed. The compressor case halves were intact, but the diffuser scroll exhibited circumferential rubbing consistent with impeller blade contact. The accessory gearbox contained metallic chips, and binding was noted during rotation of the pump gear train.
The turbine section had molten metal deposits throughout. The fractured No. 2 bearing was an FAA-Parts Manufacture Approval replacement part manufactured by Timken Alcor Aerospace Technologies, Inc.
Examination at the NTSB Materials Laboratory showed the ball retainer fractured, with damage preventing determination of fracture mode. The outer raceway had scoring, plastic deformation, and adhesive wear. Balls had flat spots consistent with adhesive wear, and some were reduced in diameter. Crater-like pitting and deposition of material were observed on the side of the No. 2 bearing's outer race and on the mating diffuser bearing housing shoulder. Energy dispersive spectroscopy revealed deposits of chromium consistent with material transfer. The features were consistent with damage produced by electrical arcing. Metallic splatter deposits were found on the oil slinger, consistent with fused metal ejected from the gap between the oil slinger and oil seal.
Caution/Warning System
The caution and warning light system was examined. The "Engine Chips" modular unit did not illuminate when the PRESS TO TEST switch was depressed, but illuminated when the actual modular unit was depressed. Disassembly revealed that the grounding contact collar was pulled back and wedged, preventing the indicator module ground from making contact with the switch housing ground unless the module face was pushed and held in. This condition would prevent the engine chip detector caution light from illuminating if metallic chips grounded either of the two engine chip detector plugs.
Additional Information
The Rotorcraft Flight Manual states that if an Engine Chips light illuminates, the pilot is to land as soon as possible and inspect the chip detectors. The Maintenance Manual recommends cleaning the magnetic drain plugs and performing a 30-minute ground run at power with rotor turning, observing engine operating limits and chip warning lights. The helicopter manufacturer noted that the 369D model's FAA certification basis does not include requirements for protection from lightning strikes. The engine Maintenance Manual specifies that in the event of a lightning strike in the immediate vicinity of the engine, the engine should be removed prior to further flight, and inspections for binding, abnormal noise, oil filter, and magnetic plugs should be performed.