ROUGH AND READY, CA, USA
N8351F
Boeing 369D
The helicopter collided with trees in a mountainous area during an attempted forced landing on a ridge line following a total loss of engine power. The pilot stated that he had been airborne approximately 25 minutes when the engine began to run erratically, and a chip detector light illuminated. He was only a few feet above the trees as he maneuvered to land when the engine stopped producing power. A quick scan of the instruments revealed that there was no oil pressure or torque. The helicopter struck a tree, and fell to the ground. Examination of the engine revealed dark, cloudy oil in the gear case sump. The upper chip detector contained debris. The No. 8 bearing cavity was dry, the shaft end nut was split and off the shaft, and the bearing was destroyed. The rotor shaft exhibited scoring at the bearing race, and was dark brown in color. The No. 6/7 bearing exhibited a similar appearance. The No. 2 shaft separated forward of the No. 6/7 bearing and exhibited a dry, deep red appearance. The Nos. 6/7 and 8 bearing oil delivery tubes were clear and dry. The oil supply line to the oil delivery tubes contained no residual oil. The oil screen in the Nos. 6/7 - 8 bearing oil supply T-fitting was clear and dry. Oil analysis discovered dark oxides that were indicative of engine lubricant starvation, and friction polymers that indicated excessive internal engine stress loads. The 3-stage oil pump was disassembled. The first (pressure) and second (gear case and No. 1 scavenge) stages were intact, visibly undamaged, turned freely, and the pump drive shaft through the two stages was intact. The pump drive shaft to the third stage was sheared. An area between the second and the third (6/7 and 8 bearing scavenge) stage of the pump and the third stage gear cavity contained small chunks of metallic debris that was determined to be bearing material. The third stage gear assembly bound when turned by finger rotation. Oil supply distribution passages in the gear case casting were clear. The check valve in the Nos. 6/7 - 8 bearing oil supply line was properly assembled and pressurized air flowed through the valve in the direction of the flow arrow on the body, and the flow checked in the reverse direction. The oil pressure relief valve was also properly assembled. The relief valve spring and poppet were visibly undamaged, and the poppet seat was smooth to the fingertip. A metallurgical analysis of the oil pump gear shaft assembly found that it conformed to the requirements and specifications of the engineering drawing and that it failed in torsional overload.
HISTORY OF FLIGHT On March 10, 2000, about 1515 Pacific standard time, a Boeing 369D helicopter, N8351F, collided with trees during a forced landing following a total loss of engine power near Rough And Ready, California. A & P Helicopters, Inc., was operating the helicopter under the provisions of 14 CFR Part 91. The commercial pilot sustained serious injuries; the helicopter sustained substantial damage. The personal cross-country flight departed Reno, Nevada, about 1445, en route to Marysville, California. Visual meteorological conditions prevailed, and no flight plan had been filed. A logbook entry dated March 10, 2000, returned the helicopter to service after the exterior had been painted, a new interior had been installed, and new avionics had been installed. The company that did this work also removed and reinstalled the engine, and performed an oil and filter change. Another maintenance facility overhauled the engine compressor while the helicopter was undergoing service. The pilot spent several days at the maintenance facility as they made final adjustments. He started the engine 10-12 times a day over that time frame while maintenance technicians completed system checks. He noted no problems. On the last day, they completed tracking and balancing. They adjusted the tail rotor, checked oil, and then completed tracking and balancing of the main rotor. During preflight, the pilot noticed that the poppet valve on the secondary bypass oil filter was not out, and that area appeared dry with no leaks. He said that start was normal. It took 18 seconds to start and reached a peak temperature around 780 degrees Celsius (C). He completed a run up and departed. The pilot stated that he had been airborne approximately 25 minutes, and was in cruise at 115 knots and about 500 feet above ground level (agl). The engine was at 70 percent torque and 700 degrees Celsius. The engine began to run erratically, and a chip detector light illuminated. He noted that torque, oil temperature, and oil pressure were within their normal ranges. He decided to land on a road on a ridgeline about 1 mile ahead. He was about 75 feet from the landing area, and a couple of feet above trees when he heard terrible grinding and squealing sounds. The low rotor speed warning light illuminated, and the helicopter turned to the left. A quick scan of the instruments revealed that there was no oil pressure or torque. The helicopter struck a tree, and fell to the ground. The front of the helicopter was gone and the pilot smelled fuel, so he rolled away from the helicopter. He had a punctured lung before, and felt that this had occurred again. He said that he learned that a woman heard the helicopter enter the valley, but she called local law enforcement when she did not hear it leave. He later saw a California Highway Patrol (CHP) helicopter come across the end of the valley and then leave. Feeling that they did not see him, he rolled back to the helicopter, and called his wife from his cell phone. The CHP helicopter returned and found him about the same time as a man on a four-wheeler. He saw a flashing emergency locator transmitter (ELT) light, realized that it was still transmitting, and instructed the man on how to disconnect the battery. PERSONNEL INFORMATION A review of Federal Aviation Administration (FAA) airman records revealed that the pilot held a commercial pilot certificate with an airplane single engine land, instrument airplane, and rotorcraft-helicopter ratings. He held type ratings in the SK-58, SK-61, and SK-64 (VFR only). He held a flight instructor certificate with ratings in airplane single engine land and rotorcraft-helicopter. The pilot reported a total flight time of 17,350 hours; 16,550 were in rotorcraft. He logged 46 hours in this make and model in the last 90 days. He held a second-class medical issued on June 8, 1999, with the limitation that reading glasses must be on board, and he had a waiver for color vision. AIRCRAFT INFORMATION The helicopter was an MD 369D, serial number 170008D. A review of the helicopter's logbooks revealed a total airframe time of 15,540 hours. An annual inspection was completed on March 10, 2000, at a total time of 15,540 hours. The engine was an Allison 250-C20B, serial number CAE 830396. Total time on the engine was 13,903 hours. METEOROLOGICAL INFORMATION An aviation routine weather report (METAR) for Beale Air force Base was issued at 1455. It stated that skies were scattered at 5,000 feet, broken at 8,000 feet; visibility was 25 miles; the wind was from 220 degrees at 6 knots; the temperature was 59 degrees Fahrenheit; the dew point was 46 degrees Fahrenheit; and the altimeter was 30.32 inches of mercury. TESTS AND RESEARCH During an examination of the helicopter, the poppet valve on the secondary oil bypass filter was in the extended position. The Pilot's Operating Handbook specifies that this item should be visually checked on preflight. The pilot stated it was not extended on preflight. Investigators disassembled the filter, and retained the residual oil. The oil tank was empty, but investigators recovered approximately 1 ounce of oil from the oil tank drain. They recovered 8 ounces of oil from the oil cooler drain. The oil sample from the tank was clear while the oil samples from the filter and oil cooler were cloudy. Herguth Laboratories, Inc., examined the oil samples. They commented that the sample from the oil filter bypass was almost completely friction polymer. This indicated excessive load or stress, and they noted that this was not detrimental unless the polymer became so numerous that they blocked filters. The sample from the filter housing consisted of ferrous debris and severe sliding wear particles of a nonferrous material. The oil cooler drain sample contained a larger copper alloy sliding wear particle. There was a large percentage of dark oxides and friction polymers. They said that the dark oxides were indicative of lubricant starvation; the friction polymers indicated excessive stress loads. The oil tank drain sample had ferrous particles; the largest particle was 40 by 33 microns. There was a high percentage of inorganic crystalline contaminants. Technicians at Rolls-Royce Engine Services, Oakland, California, disassembled and examined the engine under the supervision of a National Transportation Safety Board investigator on March 16, 2000. The engine exhibited impact damage to the burner can assembly, the compressor discharge tubes, and the exhaust nozzles. The starter-generator was not shipped with the engine. The fuel, oil, and electrical interfaces to the helicopter had been disconnected at their normal service disconnects, except the power control lever. It broke at the adjacent bellcrank, and the recovery agent shipped it with the bellcrank bracket attached. Data plates attached to the engine indicated overhauls of the compressor section on January 3, 2000; the gear case assembly on March 31, 1999; and the turbine assembly October 19, 1999. The compressor shaft did not rotate by hand. The technicians drained approximately 1 pint of oil from the gear case sump. The oil exhibited a cloudy, brown appearance. The bottom magnetic plug was free of debris. However, debris covered the tip of the upper plug; flecks of brown material adhered to it. Oil in the adjacent cavity contained small flecks of visible, shiny metal. The oil screen on the top of the gear case was clean and free of debris. The No. 6/7 bearing scavenge chamber contained approximately 1 teaspoon of cloudy, brown oil. A fluid resembling jet fuel was in the lines to the fuel control unit during removal. The freewheeling clutch rotated freely when turned by hand in the counterclockwise direction, and locked when turned in the clockwise direction. With the burner can assembly removed, the No. 8 bearing cover was clean and dry with a slight greenish tint. When technicians applied air pressure to the bearing cavity, air leaked past the cover. With the cover removed, the No. 8 bearing cavity was dry, the shaft end nut was split and off the shaft, and the bearing was destroyed. The rotor shaft exhibited scoring at the bearing race, and was dark brown in color. The No. 6/7 bearing exhibited a similar appearance. The No. 2 shaft separated forward of the No. 6/7 bearing and exhibited a dry, deep red appearance. The Nos. 6/7 and 8 bearing oil delivery tubes were clear and dry. The oil supply line to the oil delivery tubes contained no residual oil. The oil screen in the Nos. 6/7 - 8 bearing oil supply T-fitting was clear and dry. The turbine and stator blades had a uniform dark brown appearance and were visibly undamaged. When technicians removed the compressor section from the gear case, there was residual oil in the No. 1 bearing supply line and scavenge line. The No. 1 bearing was clean, oil covered, and spun freely. The compressor assembly spun freely by hand after separation from the gear case, and the compressor blades appeared undamaged externally. In the gear case, the No. 3 bearing exhibited a dry appearance with areas of dark brown/bluish appearance. The inside of the gear case was moist with oil, but not fully wet as the Rolls-Royce technician said he would expect to see. When he opened the gear case, the gear trains were intact and visibly undamaged, although the input shaft of the oil pump turned with difficulty. With the oil pump removed from the gear train, the remainder of the gears turned freely. The oil spray bar (piccolo tube) orifices were open, and the inlet screen was free of debris. When the technician disassembled the (3-stage) oil pump, the first (pressure) and second (gear case and No. 1 scavenge) stages were intact, visibly undamaged, turned freely, and the pump drive shaft through the two stages was intact. However, the pump drive shaft sheared. An area between the second and the third (6/7 and 8 bearing scavenge) stage of the pump and the third stage gear cavity contained small chunks of metallic debris similar to that found on the upper magnetic particle plug. The third stage gear assembly bound when turned by finger rotation. Oil supply distribution passages in the gear case casting were clear. The technician opened the check valve in the Nos. 6/7 - 8 bearing oil supply line, and it was properly assembled. Pressurized air flowed through the valve in the direction of the flow arrow on the body, and the flow checked in the reverse direction. The oil pressure relief valve was also properly assembled. The relief valve spring and poppet were visibly undamaged, and the poppet seat was smooth to the fingertip. The Rolls-Royce Materials Process Department performed a metallurgical analysis of the oil pump gear shaft assembly. They determined that the assembly conformed to the requirements of the engineering drawing. They identified a piece of foreign material that was in the pump as a piece of steel that was typical of bearing alloy. They determined that the assembly failed in torsional overload. Technicians at MD Helicopters, Inc., Engineering, completed a visual, nondestructive examination of 10 warning and caution lights. Each light contained four bulbs. The filament of bulb No. 1 of the Generator Out light fractured and was displaced from one post, but not significantly stretched. The filament of bulb No. 2 of the Generator out light completely fractured and was lose in the bulb. It exhibited numerous loops and bends in the pieces. Bulb No. 4 was similar to bulb No. 2. The filament of bulb No. 3 burned out. The filaments of bulbs No. 2 and 3 of the Xmsn Oil Press (transmission oil pressure) completely fractured and were loose in the bulb. They had numerous loops and bends in the pieces. The filament of bulb No. 4 in the Engine Chips light did not fractured, but was displaced from one of its posts. The filament in the Press to Test light was straight with no loops or bends. ADDITIONAL INFORMATION The Safety Board investigator released the wreckage to the owner's representative.
a loss of engine power due to oil starvation. The oil starvation was due to the seizure and failure of the turbine element oil pump shaft, which was caused by debris from a failed bearing seizing the pump. A factor in the accident was the lack of a suitable place to land following the loss of engine power.
Source: NTSB Aviation Accident Database
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