HOPE, ID, USA
N98NW
Garlick UH-1H
The pilot reported that he had dropped off a load of chokers and was maneuvering to hook up to a load of logs when the engine began to make 'a weird squealing noise, followed by a constant series of compressor stalls, occurring about twice per second.' The airplane then lost all engine power, and the pilot performed a forced landing in a clearing. Post Crash Examination revealed that the No. 1 bearing (P/N:1-300-015-04; S/N:127AC) was heavily damaged. From observations of damage on the bearing raceways and the inner ring split faces, evidence indicated that both thrust and non-thrust sides of the inner ring had been misaligned, based upon ball path indications. Military records for the engine included an Unserviceable Tag. No evidence was found of specifics related to that failure code, nor was evidence found recording related corrective maintenance action
HISTORY OF FLIGHT On May 19, 1998, approximately 1015 Pacific daylight time, a Garlick UH-1H, N98NW, was substantially damaged during an emergency landing in a clearing during a logging operation near Hope, Idaho. The commercial pilot-in-command, who was the helicopter's sole occupant, was not injured. The 14 CFR Part 133 commercial flight operation was operating in visual meteorological conditions at the time of the accident, and no flight plan had been filed for the local flight which originated at a point near the accident scene. The pilot reported that he had dropped off a load of chokers and was maneuvering to hook up to a load of logs when the engine began to make "a weird squealing noise, followed by a constant series of compressor stalls, occurring about twice per second." The pilot also reported that at the time that the compressor stalls began, the master caution light illuminated. The ground crew reported that smoke and flames were emitted from the tailpipe and the pilot turned towards a clearing approximately 100 yards away. The pilot then lost all engine power, but managed to land in the clearing. Examination of the engine revealed no obvious problems. There was evidence of oil in the engine inlet. In a written statement, the pilot noted that he heard a loud noise from the engine, followed by an engine chip light. At that time, the engine was having a series of compressor stalls and it was losing engine RPM. He stated he then jettisoned the long line and headed for a clear landing area. Before reaching the clear-cut, the engine quit totally. He pushed the nose forward to gain airspeed and to attempt an autorotation. Finding a flat place to land the aircraft, he impacted approximately 100 feet from the timberline, causing substantial damage to the aircraft. AIRCRAFT INFORMATION The engine, an AlliedSignal (formerly Lycoming) T53-L-13B, serial number LE-18249B, was given a hot-section inspection by Northwest Helicopters on April 13, 1998, at 5,678 hours since new, according to records provided by the operator. The engine was then installed in N98NW. Total time since new at the time of the accident was 5,820.2 hours. Military records from Army Aviation Support Facility, Boone, Iowa, which were available to the operator included an Unserviceable Tag, dated March 18, 1994. Total time since new on that date was 5,678 hours, with time since overhaul recorded as 4,026 hours. The removal tag cites failure code SF1 (part removed for safety of flight analysis). No evidence was found of specifics related to that failure code, nor was evidence found recording related corrective maintenance action. A Northwest Helicopters work order with an April 10,1998 entry noted that the engine time since overhaul was calculated in accordance with U.S. Army Technical Manual (TM) 55-1520-210-23 as 1,561 hours. WRECKAGE AND IMPACT INFORMATION On scene investigation was conducted by FAA inspectors. A diagram provided by FAA on-scene inspectors is attached. TESTS AND RESEARCH Disassembly and inspection of the engine were performed at AlliedSignal facilities in Phoenix, Arizona. During the course of disassembly, it was found that the front nut, which clamps the bevel gear, No. 1 bearing, and the face seal, was loose on the shaft. The nut could be easily turned by hand. The locking cup was still attached and engaged with the nut. The No. 1 bearing (P/N:1-300-015-04; S/N:127AC) was found to be heavily damaged. This bearing was evaluated by metallurgists at AlliedSignal (excerpts of the complete report are attached). From observations of damage on the bearing raceways and the inner ring split faces, evidence indicated that both thrust and non-thrust sides of the inner ring had been misaligned, based upon ball path indications. The cage was broken in pieces; the outer ring raceway was heavily damaged and covered with bronze material transferred from the cage. The lower part of the face seal runner was melted into the bearing thrust-side inner ring. Both the thrust inner ring and the seal runner were completely discolored. The non-thrust side of the bearing inner ring did not turn blue, indicating (according to AlliedSignal) that the bearing was still receiving cooling from the oil. All ball surfaces were heavily deformed and discolored dark blue. AlliedSignal metallurgists noted that: 1) The exact cause of damage could not be determined. 2) It appeared that the No. 1 bearing was misassembled, allowing inner ring misalignment, which resulted in severe ball excursion and ultimate cage fracture. 3) The engine continued to operate, resulting in bearing overheating and melting of the aft inner ring into the seal runner. 4) The loss of nut clamping load appeared to be due to the reduction in length of the clamp stack members resulting from the melting of the bearing inner race into the seal runner. ADDITIONAL INFORMATION The wreckage was released to the owner's representative, on February 5, 1999. The wreckage remained in storage at Northwest Helicopters' facility in Olympia, Washington.
Failure of a misaligned main bearing in the engine. Factors include returning a previously unairworthy-tagged engine to service by the operator's maintenance personnel without sufficient information to identify and correct an unknown engine deficiency.
Source: NTSB Aviation Accident Database
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