RIFLE, CO, USA
N617DE
Bell 206 L-3
While on a cross-country positioning flight in cruise flight, the helicopter's engine lost partial power, and the pilot conducted an autorotation to a field, which was rough and uneven. During the landing sequence, the lower wire cutter dug into the uneven ground, the helicopter rocked forward and the skid support cross tubes buckled aft. As the helicopter settled, a main rotor blade struck the left winglet of the horizontal stabilizer, and the tail boom was wrinkled. Examination of the engine revealed that the angular contact ball bearing on the power takeoff shaft had failed. The balls from the bearing had fallen into the gearbox oil sump, and a ball had lodged in the oil exit port, blocking the flow of oil out of the gearbox. The gearbox filled with oil, the oil tank emptied, and power section components began to overheat due to lubricating oil starvation. Engine records provided evidence that during maintenance performed 28.7 hours prior to the engine failure, repair station personnel had removed, inspected and reinstalled the failed bearing. Examination of the bearing provided evidence that it had been pressed apart and reassembled with the outer race reversed. The manufacturer authorizes no disassembly of the bearing. According to the manufacturer, with the outer race reversed, the bearing will immediately start to deteriorate when placed in service.
On November 24, 1999, at 1230 mountain standard time, a Bell 206 L-3 helicopter, N617DE, owned by the Department of Energy and operated by Western Area Power Administration, sustained substantial damage during an emergency landing approximately 8 miles south of Rifle, Colorado. The airline transport certificated pilot and sole occupant was not injured. Visual meteorological conditions prevailed for this public use positioning flight operating under Title 14 CFR Part 91 and a company VFR flight plan was on file. The flight departed Montrose, Colorado, at approximately 1200 on a positioning flight to Craig, Colorado. While in cruise flight at 12,000 feet above mean sea level (MSL), a partial loss of engine power occurred, which necessitated an autorotation to landing in rough terrain approximately 2 miles from the Rifle airport. According to the pilot, his first indication of a problem was a yaw to the right and the illumination of the engine chip light on the annunciator panel. He said he entered autorotation, made a "mayday" call and assessed the situation. In progressing through the emergency evaluation, the pilot determined that he had complete control and had some power, which he utilized to pass over mountainous terrain that was beneath the helicopter's flight path. When smoke emanating from the engine compartment appeared in the rear view mirror, the pilot secured the engine and did a full autorotative landing to a field. Although overgrown with vegetation, the field had been plowed at some point in the past and contained a furrowed surface. The helicopter landed perpendicular to the furrows and slid forward about one skid length. Due to the terrain surface, the lower wire cutter dug in resulting in a forward rocking movement of the helicopter. The skid support cross tubes buckled aft, and as the helicopter settled, a main rotor blade flexed downward and contacted the left winglet of the horizontal stabilizer resulting in damage to the winglet and buckling of the tail boom just aft of the fuselage attach point. External examination of the engine, an Allison 250-C30P, serial number CAE 890136, provided evidence of a catastrophic internal failure. After the helicopter was recovered, the engine was removed and, along with the engine records, was shipped to the Rolls Royce Allison factory in Indianapolis, Indiana, for detailed internal examination. Present at the examination were the NTSB Investigator-In-Charge, and representatives from the Department of Energy, Allison Engines, and Dallas Airmotive. A review of the engine records provided information that the engine was a rental from Dallas Airmotive. It was a temporary installation due to the original engine being at Dallas Airmotive for a 2,000-hour overhaul. The initial inspection focused on the oil line from the accessory gearbox since examination provided evidence that this line had oil dripping from its lowest point and the oil tank was empty. Both main oil lines were tested and their fireproof coverings were removed. They were found to be intact. Both chip detectors were removed and inspected. The lower plug had a 1/32 of an inch piece of metal on it. The upper plug was covered with metal particles. The generator was removed and oil flowed from the splined drive. The lower chip detector port was inspected and a ball bearing was observed obstructing the port. The ball was displaced from the port and 5.75 quarts of oil were drained from the gearbox. The oil was dark colored and had a burned aroma. The engine oil filter was free of debris. The airframe scavenge oil filter button was not popped, but the filter contained shiny metal slivers and metal fragments. N1 was found to be free and shafting was continuous. N2 rotation was rough and noisy and shafting was continuous to the main gearbox. Continuing examination of the accessory gearbox produced the following information. * The double lip seal on the forward end of the power takeoff shaft (PTO) was displaced forward. * The double lip seal on the aft end of the PTO was damaged and displaced. * The seal on the fuel pump drive shaft was displaced from its race. * All accessory component drive shafts were in place; however, the drive splines for the power turbine governor did not rotate when the 4th stage turbine wheel was hand rotated. * There was oil dripping from the pressure oil lines to the numbers 6, 7 and 8 bearings. The oil was dark in color and had a burned aroma. * The number 6, 7 and 8 oil sumps contained only small amounts of oil, which was dark in color and had a burned aroma. * The turbine to compressor coupling was dry and contained coking at the middle section of the coupling. * When the accessory gearbox was opened, 4 ball bearings were observed loose on the cover side. * When the helical PTO shaft was lifted, the outer race of the angular contact ball bearing, part number 6889326, was dislodged from the bore on the cover side. * The bearing separator remained in the bore and the inner race remained on the PTO shaft. There were no ball bearings in the bore. * All 13 ball bearings were recovered from the cover side of the accessory gearbox. * The inner race was correctly installed on the PTO shaft; however, the bearing was assembled incorrectly with the outer race reversed. Tests and research provided the following information: * The gearbox assembly service record from the engine logbook provided information that the gearbox was split and had work performed on November 1, 1999, 28.7 hours prior to the accident. During this maintenance action, the failed bearing was reportedly removed from the PTO shaft, inspected, and re-installed. * According to Allison, there are no provisions to disassemble this bearing for inspection. It is a "remove and replace" item. * Allison provided information that, in normal service, this bearing receives thrust loading of approximately 470 pounds of force during engine operation at 650 horsepower and 6,016 revolutions per minute. In addition, the manufacturer stated that they have not tested the load bearing capability of the bearing with either race reversed; however, by design, such a fabrication would start to deteriorate immediately upon being placed in service.
a forced landing on rough, unsuitable terrain. A contributing factor was the partial loss of engine power, which resulted from improper maintenance by repair station personnel.
Source: NTSB Aviation Accident Database
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