Bonifay, FL, USA
N425LS
GULFSTREAM-SCHWEIZER A/C CORP G-164B
The commercial pilot was conducting a cross-country positioning flight in the turboprop airplane. The pilot reported that, while on approach to the destination airport, the propeller began wind-milling, and "pieces of metal" began coming out of the right engine exhaust duct. The pilot subsequently conducted a forced landing, during which the airplane struck trees. Postaccident examination of the engine revealed that the No. 2 bearing oil nozzle jet was partially blocked, which resulted in oil starvation and the subsequent disintegration of the No. 2 roller bearing. The material blocking the oil nozzle jet was consistent with material used in the composition of the bearing races and rollers. A review of maintenance records revealed that the No. 1 engine bearing had failed about 1,000 flight hours before the accident and was replaced along with the No. 2 bearing. In addition, the Nos. 1 through 5 bearings were replaced about 300 flight hours before the accident. The investigation could not determine if the No. 2 bearing oil nozzle jet was blocked by bearing material as a result of the previous bearing failure or if the blockage developed during the engine's subsequent operation.
On July 25, 2014, about 0823 central daylight time, a Gulfstream-Schweizer G-164B, N425LS, collided with trees and the ground during a forced landing near Bonifay, Florida. The commercial pilot was not injured, and the airplane was substantially damaged. The airplane was registered to a private individual and operated by Croom Aviation, under the provisions of 14 Code of Federal Regulations as a Part 91 positioning flight. Visual meteorological conditions prevailed for the flight that originated at Donalsonville Municipal Airport, Donalsonville, Georgia, about 0800, and was destined for Tri-County Airport, Bonifay, Florida.According to Federal Aviation Administration (FAA) records, the airplane was manufactured in 1979, and operated with restricted category airworthiness certificate for agriculture and pest control purposes. It was originally equipped with a Pratt & Whitney R985-AN-14B radial engine, but was subsequently changed with the installation of a Pratt & Whitney Canada PT6A-27 turboprop engine. The pilot stated that before departure he added 1 quart of oil to the engine, and then departed with about 60 to 70 gallons of fuel on-board. The flight proceeded towards the destination airport and with it in sight, as he reached to reduce power, the propeller began wind milling and the engine, "went to screaming, pieces of metal [were] coming out [of the] right exhaust [duct] and down [the] right side of [the] aircraft." He immediately added, "full power, [propeller] and fuel trying to get a response and nothing." The airplane struck trees during the ensuing forced landing, and came to rest on the ground. Following recovery of the airplane, the engine was sent to the manufacturer's facility in Montreal, Canada, for disassembly examination with oversight from a representative of the Transportation Safety Board of Canada. Examination of the engine revealed the gas generator case housing interior contained two holes of varying sizes and numerous outward dimples and pockmarks around the housing interior. The 1st and 2nd stage compressor blades exhibited circumferential rubbing at the blade tips, while the 3rd stage blades exhibited heavy rubbing and tearing due to contact with the shroud and adjacent stator. Nine blades and root sections were displaced from the disk; two of which were not recovered. Examination of the Nos. 1 and 2 bearings which supported the compressor rotor revealed no indications of operational distress to the No. 1 ball bearing; however, the No. 2 roller bearing elements and cage were disintegrated; the cage was fractured into multiple sections and displayed severe oxidation, mechanical damage, and deformation. Twelve of the sixteen rolling elements of the bearing were recovered and displayed severe heat oxidation and mechanical damage. The bearing air seal rotors displayed heavy circumferential scoring and machining due to radial contact with the air seal rotors knife edges. The No. 2 bearing inner and outer races were coated with heat fused melted material. The No. 2 bearing oil nozzle was removed and flow tested, which revealed it was obstructed. Subsequent x-ray inspection of the nozzle revealed material build-up to the top of the nozzle jet. Components of the No. 2 bearing and the blockage from the No. 2 bearing oil nozzle were submitted to the Pratt and Whitney Canada Materials Engineering Laboratory for analysis. The examination of the bearing components revealed the bearing races and cage material was consistent with drawing requirements; however, the hardness of the outer race and rolling elements could not be determined due to heat damage. The analysis of the blocked material indicated it was consistent with the material used in the composition of the bearing races and rollers. Further examination of the engine revealed the compressor turbine displayed circumferential rubbing with frictional heat discoloration and material transfer due to contact with the shroud. The disk downstream side displayed circumferential rubbing due to contact with the power turbine guide vane ring. The oil filter and reduction gearbox chip detector were clean. According to maintenance records, the Pratt & Whitney Canada PT6A-27 engine, serial number PCE-40160, that was installed at the time of the accident, was installed in accordance with FAA supplemental type certificate SA1377GL. On April 6, 2012, at an engine total time of approximately 18,045 hours, the engine was removed due to a report of failure of the No. 1 bearing. The engine repair consisted in part of installing a new No. 1 bearing and main oil filter, replacement of the No. 2 bearing, cleaning of all oil wetted passages, and replacement of the oil cooler. The engine was reassembled, ground run with no discrepancies noted, and was approved by an airframe and powerplant mechanic for return to service. The engine was installed on the accident airplane on April 13, 2012. A subsequent 100-hour inspection was performed on August 27, 2012, in which the oil filter was cleaned, and a check of the oil strainers and chip detectors revealed no metal was found. Further review of the maintenance records revealed that on March 7, 2013, at an engine total time of approximately 18,773 hours, the engine was disassembled due to a report of vibration and unusual noise. As part of the repair, the Nos. 1 thru 5 bearings were removed and replaced with overhauled bearings, and the No. 6 bearing was inspected and found to be serviceable. Following repair, the engine was installed in the accident airplane on June 14, 2013; the maintenance record entry did not indicate whether the oil strainers, oil filter, or chip detectors were checked. The engine was removed and reinstalled about 2 months later, after replacement of the compressor turbine blades. Following installation, routine maintenance, as well as a hot section inspection was noted; the hot section inspection occurred on July 9, 2014. There was no record that any metal was detected in any of the checks of the oil strainers or chip detector at that time. As of the last hot section inspection, the engine had accrued approximately 287 hours since the overhauled No. 2 bearing was installed. The engine total time at the last hot section inspection was 19,059 hours. According to the engine maintenance manual, if oil system contamination is suspected, a reverse flush of the oil system including the oil-to-fuel heater must be performed, and the oil cooler must be rejected. The maintenance manual also indicated that identification of the contaminated material by analysis determined the steps to perform, which may require overhaul of the engine.
A partial blockage of the No. 2 bearing oil nozzle jet by bearing material, which resulted in oil starvation and the subsequent failure of the No. 2 bearing and total loss of engine power.
Source: NTSB Aviation Accident Database
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