KAMUELA, HI, USA
N12NT
Aerospatiale AS350BA
A hard autorotation landing resulted from a loss of engine power in the takeoff initial climb. Inspection of the engine after the accident revealed that the engine gas generator compressor/turbine shaft was seized. The engine was overhauled 61 hours prior to the accident. The gas generator turbine aft support bearing was found dislodged from the bearing support cage. A circlip used to retain the bearing in the cage was not present and there was no evidence of the circlip having been installed during overhaul. The autorotation was made to an area of dirt and rocks that had a slight upslope.
On October 22, 2000, at 0807 hours Hawaiian standard time, an Aerospatiale AS350BA, N12NT, was substantially damaged during an autorotative emergency landing following loss of engine power about 1 mile west-southwest of the Waimea-Kohala airport at Kamuela, Hawaii. The commercial certificated pilot, the sole occupant, received serious injuries. Visual meteorological conditions prevailed for the positioning flight that was operated by Mauna Kea Helicopters, under 14 CFR Part 91. The helicopter was departing from the airport at the time of the engine failure, destined for a nearby resort hotel. No flight plan was filed. The autorotation was performed to an upsloping area of dirt and rocks. Inspection of the engine after the accident revealed that the engine compressor was seized. The engine was overhauled 61 hours prior to the accident. The engine is comprised of five modules. Module 1 is overhauled on-condition and was not serviced at the overhaul. Turbomeca Engine Corporation of Grand Prairie, Texas, overhauled modules 2 and 3, and Acro Aerospace, Inc., of Richmond, BC, Canada, overhauled modules 4 and 5. The five modules were assembled together and installed in the helicopter by the operator. The engine was examined by Safety Board investigators at the facilities of Turbomeca Engine Corporation on December 7, 2000. The rotating assembly (compressor and turbine) of the gas generator section (N1, modules 1, 2 and 3) of the engine was seized and the power turbine assembly and output gearbox (N2, modules 4 and 5) was free to rotate. When modules 2 and 3 were separated, the compressor and accessory case (modules 1 and 2) rotated freely and the combustion section and turbine (module 3) remained seized. Module 3 was difficult to disassemble due to damage at the rear bearing area. Further examination revealed the turbine rear support bearing (bearing, Turbomeca part number 9609000153) was backed out of the bearing support housing (cage, part number 0292502630). Ordinarily the bearing is retained in the housing by a circlip (part number 9560119360), however, no evidence of presence of the circlip was found. The circlip retaining groove in the support housing was visibly undamaged. An additional party to the investigation was Mr. Joe Braz of Acro Aerospace, Inc, Richmond, BC, Canada. The wreckage was released to the owner on December 22, 2000.
A total loss of engine power due to the failure of the engine manufacturer's repair station personnel to install a circlip during engine overhaul, which resulted in the turbine assembly aft support bearing becoming dislodged and seized on the shaft. A factor in the accident was the rough and uneven nature of the landing site terrain.
Source: NTSB Aviation Accident Database
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