History of Flight
On May 3, 2014, at approximately 1130 mountain daylight time, a Bell 407 helicopter, registration N407MH, experienced an engine chip detector light followed by a loss of engine power. The pilot executed a forced landing to snow-covered mountainous terrain above 10,000 feet MSL near Telluride, Colorado. The commercial pilot and two crew members were not injured. The helicopter, registered to and operated by Classic Helicopters, Inc., of Ogden, Utah, was conducting a search and rescue flight under Part 135 VFR. The flight originated from Moab, Utah.
The pilot reported conducting a search for a missing person for the San Miguel Sheriff's Department. After completing several search grid lines, the pilot made a right turn when the engine noise changed. Shortly thereafter, the engine chip detector light illuminated, followed by a FADEC degrade light. The helicopter was about 200 feet AGL. The pilot began descending toward an open snow-covered meadow, but engine RPM degraded, prompting an autorotation. The helicopter touched down with little forward airspeed, bounced, and the left skid caught on an object under the snow, causing the helicopter to roll onto its left side and come to rest. All three occupants exited without injury.
Aircraft Information
The helicopter was a Bell Helicopter Textron Model 407, serial number 53100, configured for emergency medical use. It was powered by one Rolls-Royce M250-C47B turboshaft engine, serial number 847016, rated at 650 shaft horsepower. The helicopter had a 150-hour engine inspection on April 30, 2014, at an airframe time of 10,724.6 hours. Total airframe time at the accident was 10,730.1 hours.
Personnel Information
The 32-year-old pilot held a commercial pilot certificate with helicopter and instrument ratings, as well as a flight instructor certificate. He reported 4,300 total flying hours, with 740 hours in the Bell 407, and 42 hours in the preceding 30 days. He held a second-class medical certificate dated April 22, 2014, with no restrictions.
Wreckage and Impact Information
The left side of the passenger compartment showed inward buckling and skin wrinkles. Inward crushing damage was also observed on the upper rear engine cowling and engine exhaust. The lower left and lower right forward Plexiglas windows were broken. The tailboom was severed just aft of the main fuselage, and the tail rotor gearbox was torn out. The main rotor system remained attached, but three of four main rotor blades were bent and broken. Flight control examination revealed no preimpact anomalies.
Post-accident engine examination showed continuity in the gas producer and power turbine drive train, but resistance to gas producer rotation and scraping of the power turbine. Ferrous debris was found in the engine scavenge oil filter. The engine was shipped to the manufacturer for further analysis.
Tests and Research
At Rolls-Royce Corporation in Indianapolis, Indiana, on June 3-4, 2014, examination revealed the power turbine thrust (No. 5) bearing was dry, gray/black, heavily worn, with no recognizable ball elements. Melted metal deposits were present. The ball separator was heavily scored with enlarged ball pockets. Other power turbine components showed rotational contact damage consistent with loss of radial and axial positioning normally provided by the No. 5 bearing.
The No. 4/5 bearing oil jet appeared unobstructed. However, the gearbox cover oil transfer passage was obstructed. Visual inspection showed light could not be observed through the passage, and alcohol did not pass. Radiographic inspection revealed a threaded insert from a repair that restricted the opening. A calibrated flow test showed less than 2 percent of design flow. Ultrasonic cleaning produced particles consistent with coked oil and scarf. Metallographic examination found deposits consistent with coked oil near a circumferential gap between the insert and cover.
The engine was manufactured in 1966. The gearbox cover, P/N 23065470, serial number 44193, was original and bore a material review board (MRB) symbol indicating a threaded insert was installed during original manufacture. The gearbox had been disassembled seven times in service, with no records of additional repairs to the oil delivery tube port.