Meridian, MS, USA
N697MA
Piper PA-32R-301
The pilot had been airborne for about 45 minutes practicing turns and instrument approaches in VFR condition. He had completed a practice instrument approach to runway 1, was following the published missed approach, and the flight had attained an altitude of about 500 to 600 feet when he reported that he heard a "...loud pop, and the engine quit immediately...[without] warning of the impending engine stoppage." He declared an emergency, was cleared to land, turned left onto a short base leg to runway 1, could not maintain altitude, and he could not make it to the runway. The pilot elected to land in a field, and impacted with trees short of the runway threshold. An engine disassembly revealed that the engine failure was due a broken crankshaft gear bolt, and the separation of the crankshaft gear from the rear of the crankshaft. A laboratory examination of the failed crankshaft gear bolt, revealed that crankshaft bolt part number STD-2209, had failed due to hydrogen embrittlement. The NTSB Materials Laboratory's analysis found that the preponderance of evidence and reference information indicated that the manufacturing cycle (plating/bake delay/bake itself) was the most likely source of hydrogen embrittlement.
On June 7, 2002, about 1348 central daylight time, a Piper PA-32R-301, N697MA, registered to a private individual, impacted with the ground during a forced landing near Key Field Airport, Meridian, Mississippi. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 local personal flight. The airplane was substantially damaged. The private-rated pilot reported serious injuries. The flight had originated from the same airport about 1300. The flight had been airborne for about 45 minutes, while the pilot practiced turns and instrument approaches in VFR conditions. He had completed a practice instrument approach to runway 1, was following the published missed approach, and the flight had attained an altitude of about 500 to 600 feet, when the pilot reported, that he "...heard a loud pop, and the engine quit immediately. There was no warning of the impending engine stoppage." He declared an emergency, was cleared to land, turned left onto a short base leg to runway 1, could not maintain altitude, and he could not make it to the runway. The pilot elected to land in a field, and impacted with trees about 2 miles southwest of the runway threshold. The FAA inspector's stated that he had arrived at the crash scene at 1500, on June 7, 2002. The "...aircraft was upside down with the right wing separated from the fuselage." The FAA inspector stated that he observed a "faint smell of fuel with little foliage damage." The fuel cells were found "compromised by impact, but there was fuel still in the cells." The propeller tips were "bent uniformly aft" indicating "no power at impact." One blade was separated from the hub. According to the New Piper Corporation's investigator's preliminary report, he examined the crash site, "...5 days after the accident...no evidence of internal engine failure was noted...indications of fuel spray on the foliage was inconclusive. Numerous branches were broken and the flight path was evident through the trees. No cut branches or prop strikes were noted. Aircraft fueling records were not available at the time of the investigation...further investigation by Lycoming is planned in the near future." (See the copy of the New Piper Corporation's investigator's report, an attachment to this report). According to the FAA, Airworthiness inspector's statement, he assisted an investigator from Textron Lycoming with the inspection of the engine from N697MA, on June 20, 2002. The inspector stated that "...our preliminary inspection led us [FAA and Lycoming] to the conclusion that engine model IO-540-K1GS; S/N L-25968-48A had an internal failure." (See the copies of the FAA inspector's statements, an attachment to this report). According to the Textron Lycoming investigator's field notes (no date), "...the engine was rotated...crankshaft continuity was established, but no valve train continuity could be verified. The vacuum pump was removed and the accessory housing was inspected using a lighted bore scope, and no accessory gear movement was observed. All cylinders were inspected using a lighted bore scope, all pistons were observed rotating properly. The oil measuring gauge reveled 6.5 quarts of what appeared to be engine oil, no contaminants were noted...at this point in the investigation, it was decided that the inspection should be discontinued and the engine be removed and returned to Textron/Lycoming for further teardown inspection." (See the copy of the Textron/Lycoming investigator's report, an attachment to this report). On July 15, 2002, the engine from N697MA was disassembled under the supervision of the FAA at the facilities of Lycoming Engines, Williamsport, Pennsylvania. The engine examination revealed that the engine failure was due to a broken crankshaft gear bolt, and the separation of the crankshaft gear from the rear of the crankshaft. The crankshaft, crankshaft gear, crankshaft gear bolt, and crankshaft dowel were sent to the Lycoming Materials Laboratory for further evaluation (See the copy of the Textron/Lycoming engine teardown report, an attachment to this report). The Lycoming Materials Laboratory Report, dated August 6, 2002, revealed that crankshaft bolt part number STD-2209, was "...the primary cause of engine failure." According to the Lycoming Materials Laboratory Technical Report, visual examination revealed the crankshaft gear bolt fractured through "...the second to fifth threads from the shank. Two overlapping cracks extended through approximately 270 degrees of the circumference were also observed in the twelfth and thirteenth threads from the shank." A "possible" crack was observed in the "radius" under the head, and was "confirmed" by fluorescent magnetic particle inspection. "...Intergranular separation on [all the cracks] indicated all were caused by hydrogen assisted cracking [hydrogen embrittlement]." This was based upon the observations of the fatigue on the crack in the second and fifth threads, the location of laboratory-produced overload on cracks in the twelfth and thirteen threads, and the varying depth of intergranular separation on the crack under the head. The Lycoming Materials Laboratory Report further stated, "...SEM-EDAX (energy dispersive x-ray analysis) examination revealed the plating was zinc. Zinc plating per AMS 2402 was allowed as an approved variant to the engineering drawing requirement of cadmium under Textron Lycoming SDMR 78347 approved July 19. 1995." (See the copy of the Textron/Lycoming Materials Laboratory Report, an attachment to this report.) A history of the engine revealed that the engine was shipped as a new IO-540-K1G5, L-25968-48A from Lycoming Engines, Williamsport, Pennsylvania, to The New Piper Aircraft, Vero Beach, Florida, on December 26, 1996. There were no records indicating that the accident engine was returned to Lycoming until after the accident on June 7, 2002. The aircraft was released to Mr. Dennis Krueger, on behalf of the owner's insurance company, on July 30, 2002. The engine and crankshaft bolt were released to Mr. Dennis Krueger, on April 16, 2003.
inadequate quality control of the manufacturing processes of the crankshaft gear bolt, resulting in failure of the gear bolt, due to hydrogen embrittlement, a total loss of engine power, and damage to the airplane during the subsequent forced landing.
Source: NTSB Aviation Accident Database
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