LUCERNE VALLEY, CA, USA
N5016G
Bell 206B
The pilot had been flying for about 25 minutes when he noticed that the oil pressure gauge and torque gauge were fluctuating. He initiated an approach to a precautionary landing spot on an asphalt pad. About 150 feet agl, the engine quit and the pilot autorotated to touch down on a paved road. The main rotor blades severed the tail boom aft of the horizontal stabilizer. The engine had received some maintenance work and had been reinstalled in the helicopter the night before the accident, at which time the pilot performed a test run and leak check of the engine, with no noted discrepancies. The pilot further stated that the engine had been running normally until the fluctuation of the oil pressure and torque gauges. During an examination of the engine, the oil output line was connected, but loose, and oil was seen dripping from the fitting area. Oil was observed over most of the fuselage and underneath the engine. There was approximately 1 pint of oil found in the sump. Further teardown of the engine revealed that the number 8 bearing was destroyed and no oil was found throughout the lubrication system. The Bell Helicopter maintenance manual specifies a torque value for the fitting on the oil output line; however, the mechanic who installed the engine reported that he did not use a torque wrench to tighten the line because he would have had to remove some other lines to get to it and he was in a hurry.
On August 4, 1998, about 0745 hours Pacific daylight time, a Bell 206B, N5016G, experienced a loss of engine power near Lucerne Valley, California. The aircraft sustained substantial damage in the ensuing forced landing, and the commercial pilot, the sole occupant, was not injured. The helicopter departed the Riverside, California, airport at 0720, and was en route to Flagstaff, Arizona, with a final destination in Oklahoma to fulfill a government work contract. The aircraft was being operated by Rainbow Helicopters, Inc., Redmond, Oregon, and the flight was conducted as a positioning flight under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed along the route of flight and a VFR flight plan was filed. The pilot reported that he had been flying for about 25 minutes when he noticed that the oil pressure gauge and torque gauge were fluctuating. He initiated an approach to a precautionary landing spot on an asphalt pad. About 150 feet agl, the engine quit. The pilot autorotated and touched down on a paved road. The main rotor blades severed the tail boom aft of the horizontal stabilizer. Review of the aircraft maintenance records disclosed that the engine had been accumulating metal on the top and bottom magnetic plugs. The pilot had been in Riverside on two recent occasions to have repairs done to the engine. The engine was reinstalled in the helicopter the night before the accident, and the pilot and a mechanic performed a test run and leak check of the engine. No discrepancies were reported. The pilot further stated that the engine had been running normally until the fluctuation of the oil pressure and torque gauges. The helicopter and engine were examined following recovery of the aircraft. Fuel was present in the lines, fuel pump, and fuel control. The fuel filter was clean and the fuel bowl contained fuel. The fuel control to fuel nozzle line contained fuel. No damage was observed to the engine deck or engine mounts. Oil was noted on the bottom pan, as well as over the fuselage and tail cone. The engine oil tank was intact and approximately 4 ounces of oil were visible in the bottom. There was no evidence of oil spillage from the tank, and all fluid line connections were secure except for the tank oil output line, which was loose. Oil was observed dripping from the fitting area. The Safety Board conducted a teardown examination of the engine on August 19, 1998. The Nos. 6, 7, and 8 bearings were without lubrication, with balls that were flattened and out of round. Heat distress was evident in the bearings. The power turbine labyrinth seal, portions of the power turbine inner shaft, portions of the compressor to turbine shaft, and portions of the hub of the third stage power turbine wheel displayed signs of heat distress. According to the representative from Rolls-Royce Allison Engines, the oil starvation was the result of the loose scavenge engine oil output line which allowed oil to pump overboard, emptying the oil tank. This event involved the nonpressure side of the oil system, therefore, he opined that it was possible that the engine pressure indicating instruments (oil pressure and torque) would not have provided indications at the onset. Indications would have shown after the problem progressed. A copy of his report is appended to this file. In a written statement, the mechanic who installed the engine stated that he used the Bell Helicopter Textron - 206B3 Maintenance Manual to install the engine. He reported to the Federal Aviation Administration inspector who interviewed him that he did not use a torque wrench to tighten the oil output line because he would have had to remove some other lines to get to it, and he was in a hurry. The Bell Helicopter Standard Practices Manual, which is applicable to all Bell Helicopter models, lists the torque values for all basic dash-numbered fittings or nuts. The manual also lists formulas to obtain the correct indicated torque value when using nonconcentric attachments. Furthermore, the mechanic said he did not sign off his work in the airframe logbook, reporting that he thought the repair facility would do that. He wrote that he felt that ". . . the lack of communication and sense of urgency in completing the job was an attributing factor in this accident." A copy of his written statement is appended to this file.
The failure of the mechanic who installed the engine to follow proper procedures by insuring the proper torque to the oil output line, resulting in a loose fitting, oil loss and subsequent bearing failure.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
