Warren, AR, USA
N9414Y
BEECH N35
The pilot reported that the engine lost power during the initial climb. He then established a glide in an attempt to return to the airport; however, due to "strong" wind, the airplane landed "abruptly short of the runway." A postaccident engine examination revealed that the crankshaft had fractured due to fatigue through the No. 3 cheek immediately aft of the No. 2 main bearing journal. Portions of the saddle bore diameter at the nose of the crankshaft were oversized. The crankcase No. 2 main bearing saddle exhibited longitudinal deformation adjacent to the bore with fretting and galling on the saddle landings. The No. 1 main bearing shells were deformed; the No. 2 main bearing shells were worn, deformed, and partially split. The remaining bearings exhibited helical lines that matched the machining lines on the crankcase main bearing saddles. The tin coating had been worn away except around the oil transfer holes. The appearance of the main bearing shells was consistent with the bearings shifting during operation due to insufficient crush, which was likely caused by the oversized main saddle bore diameters. Maintenance records indicated that the engine was disassembled about 15 months before the accident due to a propeller strike. At that time, maintenance personnel cut the crankcase mating surfaces and resized the saddle bores. The engine had accumulated about 16.5 hours since the engine was reinstalled. It is likely that maintenance personnel improperly resized the saddle bores during the engine maintenance.
On April 15, 2013, about 0945 central daylight time, a Beech model N35 airplane, N9414Y, was substantially damaged during a forced landing following a loss of engine power after takeoff from the Warren Municipal Airport (3M9), Warren, Arkansas. The pilot and passenger sustained minor injuries. The aircraft was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight. An instrument flight rules flight plan had been filed, but not yet activated. The flight was originating at the time of the accident. The intended destination was the Mena Intermountain Municipal Airport (MEZ), Mena, Arkansas.The pilot reported that he had departed from runway 21 (3,829 feet by 75 feet, asphalt) at 3M9 and climbed to 700 feet mean sea level (msl). As he started a right turn to the west, about 1,000 feet msl, the engine lost power. He established a glide in an attempted to return to the airport. However, due to "strong" winds, the airplane contacted the ground "abruptly short of the runway." A postaccident engine teardown and subsequent metallurgical examination were conducted. The crankcase was cracked starting at the number 1 cylinder head mounting stud and continuing to the top of the case. The crankcase number 2 main bearing saddle exhibited longitudinal deformation adjacent to the bore, with fretting and galling on the saddle landings. The other saddles exhibited curvilinear marks on the split plane landings and helical marks on the saddle bores, consistent with machining marks. The crankcase was re-assembled and the saddle bore diameter at the nose of the crankshaft was measured. The bore diameter was within limits in the area centered 90-degrees from the split plane. However, the bore diameter was oversized in the area centered about 20-degrees from the split plane. The bore diameter measured 2.5660 inch; the bore diameter limits were 2.5625 inch to 2.5635 inch. The crankshaft had fractured through the number 3 cheek, immediately aft of the number 2 main bearing journal. The fracture surfaces exhibited curvilinear crack propagation marks consistent with fatigue. The main bearing surface exhibited circumferential abrasion marks. The main bearing journal diameters measured within the limits for a reground crankshaft, with the exception of the number 2 journal. The number 1 main bearing shells were deformed; the number 2 main bearing shells were worn, deformed and partially split. The remaining bearings exhibited helical lines that matched the machining lines on the crankcase main bearing saddles. The tin coating on the backside of the bearings had been worn away except around the oil transfer holes. Dimensional inspection of the number 3, 4 and 5 main bearing shells were within limits. Engine maintenance records indicated that the engine was overhauled in January 2001, at 1,526.5 hours total time. According to the records, an annual inspection was completed on December 10, 2009, at 1,696.7 hours total time, with 170.4 hours since overhaul. The next entry indicated that the engine was removed from the previous airframe "for prop strike on or about 8 – 11." This entry noted the total time as 1,526.5 hours, which was the same as at overhaul about 9 years earlier. However, the time since overhaul was the same as at the December 10th annual inspection. An entry dated January 10, 2012, noted that the engine had been disassembled due to a propeller strike. At that time, the crankshaft was magnetic particle inspected with negative findings. The crankcase mating surfaces were cut and the bores were resized to the manufacturer's limits. It was subsequently installed on the accident airplane on March 5, 2013. An annual inspection was completed at that time. The recording tachometer time was noted as 216.8 hours. There were no subsequent entries in the either the airframe or engine maintenance logbooks. The recording tachometer indicated 233.31 hours after recovery of the airplane. Based on the tachometer time noted at the annual inspection, about 16.5 hours had accumulated since the inspection.
The fatigue failure of the engine crankshaft due to oversized crankcase saddle bores, which resulted from maintenance personnel improperly resizing the saddle bores during engine maintenance.
Source: NTSB Aviation Accident Database
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