St. Augustine, FL, USA
N1130T
Cessna 172S
The airplane experienced a loss of engine power due to failure of the crankshaft and separation of the propeller and propeller flange during the initial climb shortly after takeoff. The pilot reversed course and landed on a taxiway at the departure airport without further incident. At the time of the event, the airplane and engine had accumulated a total time of 399.3 hours. Metallurgical examination determined that the crankshaft separation was the result of a lubrication failure at the #2 main bearing. The lubrication failure then allowed excessive friction to overheat the bearing journal on the crankshaft producing ladder cracks in the surface and at the oil transfer hole. These cracks in turn initiated torsional fatigue cracks that ultimately lead to the separation of the crankshaft. The root cause of the lubrication failure was likely the result of intermittent oil flow to the bearing or of improper assembly (fitting) of the bearing shells to the crankshaft. Considering that the other bearings did not show distress and the short time since engine assembly, it is more likely that an assembly issue was the cause. No preexisting metallurgical or mechanical discrepancies were found with the crankshaft.
HISTORY OF FLIGHT On May 23, 2006, about 1258 eastern daylight time, a Cessna 172S, N1130T, registered to SAL Enterprises LLC and operated by Epic Aviation, experienced a failure of the crankshaft and separation of the propeller and propeller flange during the initial climb shortly after takeoff from St. Augustine Airport, St. Augustine, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 Code of Federal Regulations Part 91 ferry flight from St. Augustine to New Smyrna Beach, Florida. The airplane sustained minor damage and the commercial pilot, the sole occupant, was not injured. The flight was originating at the time of the incident. Prior to the incident flight, there had been two reported occurrences of engine roughness on this aircraft; the first report on May 21, 2006, and the second report on May 22, 2006. On May 21, approximately 45 minutes into a flight lesson, a student and instructor experienced engine roughness and an RPM drop. The flight ended with a precautionary landing at New Smyrna Beach Municipal Airport. The event was reported to the operator's maintenance personnel, and according to the operator's director of maintenance, a mechanic performed an engine run up with no discrepancies noted. On May 22, a flight student experienced a similar event with engine roughness and RPM drop, resulting in a precautionary landing at St. Augustine Airport. The intended purpose of the incident flight was to return the airplane from St. Augustine to its home base at New Smyrna Beach. The incident pilot reported that he performed a preflight inspection of the airplane and noted that the engine oil quantity was 6 quarts. He also performed several engine run-ups which included a magneto check and full rpm check and no discrepancies were noted. The flight departed and during the initial climb at 500 feet, the engine rpm decreased from 2,390 to 2,200. The pilot advised the tower controller of the power loss and had started a turn to return to the airport when he heard a "loud bang." This was followed by strong vibration of the engine and the loss of all power. He performed an uneventful forced landing on taxiway "B." Examination of the airplane by the operator's director of maintenance revealed the crankshaft was fractured inside the crankcase at the oil transfer tube location, approximately 6 inches aft of the propeller flange. The separated forward section of the crankshaft with the propeller attached was found on a runway at the airport. AIRCRAFT INFORMATION The 2005 model Cessna 172S, S/N 172S9874, was delivered new to its current owner on July 15, 2005. The airplane was used for flight training. It was powered by a Lycoming IO-360-L2A engine, S/N L-32000-51A. At the time of the incident, the airplane and engine had accumulated a total time of 399.3 hours. The most recent inspection, a Phase 1 inspection, was performed on April 21, 2006, at a total time of 350.2 hours. AIRFRAME AND POWERPLANT EXAMINATION The airplane was examined on May 25, 2006, under the supervision of an FAA inspector, by representatives from Epic Aviation, Cessna Aircraft Company, and Lycoming. Damage to the airframe was minor. The upper and lower engine cowls were damaged due to severe vibration, and the nose wheel fairing was damaged due to contact with the lower engine cowl. The fuselage skin lip, just forward of the firewall and near the lower engine mount firewall attach points, exhibited a bent area on the left side, and a small cut area on the right side. Prior to removal from the airframe, the engine was observed to have oil in the sump. The engine was removed, crated and shipped to the facilities of Lycoming in Williamsport, Pennsylvania for teardown. On June 12, 2006, the engine was disassembled under the supervision of an FAA inspector with participation of representatives from Epic Aviation, Cessna Aircraft Company and Lycoming. During engine disassembly, the engine oil filter was cut open and copper/aluminum bearing material was found. The section of the crankshaft that remained in the case, the engine case halves, and the main bearings were shipped to the NTSB Materials Laboratory in Washington, DC. Previously, the forward section of the crankshaft had been shipped to the NTSB laboratory. TESTS AND RESEARCH The crankshaft, case halves, and main bearings were examined at the NTSB Materials Laboratory in Washington, DC. The crankshaft was separated by roughly 45-degree oriented fracture planes spiraling right and left around the journal area between the #1 and #2 main bearing locations. The fractures intersected one side of the cross-hole between the main bearings. The left fracture initiated at the oil hole and propagated by very high stress fatigue. The right fracture was a series of steps and longitudinal cracks; the fracture features showed arrest marks indicating fatigue progression in multiple directions without clear origin areas. Both the #1 and #2 crankshaft main bearing journal surfaces were heavily damaged with circumferential abrasions, wear, heat tinting and galling. The #2 bearing area was most heavily damaged and contained multiple large visible cracks at the oil transfer hole. The #3 and #4 main bearing journal surfaces were not damaged and appeared to be in serviceable condition, as were all the connecting rod journals. In areas away from the journal surfaces, the crankshaft microstructure appeared typical of a quenched and tempered alloy steel with a fine tempered martensite core and a nitrided case at the surfaces. At the #1 and #2 main bearing journal surfaces, the crankshaft's microstructure was heavily disturbed and altered by localized heating and mechanical damage. The #1 and #2 main bearings, which are combined into one pair of bearing shells, were severely distorted, fractured and cracked. In comparison, no damage and very little wear was noted on the #3 and #4 bearing shells. Large areas of the bearing material layers were missing from the #1 and #2 shells and the bearing surfaces were deeply gouged in places. Both halves were cracked or fractured through the steel outer shell at the #2 journal area or between the bearing surfaces. Examination of the case halves revealed that the bearing seats for the #1 and #2 bearings displayed mechanical and thermal damage. The case surfaces were dented and marked consistent with the damage found on the bearings. The bearing seats for the #3 and #4 bearings were undamaged. The main bearing seat diameters were measured with the case halves bolted together. All diameters measured at bearings #1 and #2 were out of tolerance and this may reflect the noted damage. All oil passages through the case were checked and found open. For further details of the examination, see the Materials Laboratory Factual Report in the public docket for this investigation.
The loss of engine power due to separation of the crankshaft as a result of lack of adequate oil lubrication to the #2 main bearing. The lack of oil lubrication was most likely the result of improper assembly (fitting) of the bearing shells to the crankshaft.
Source: NTSB Aviation Accident Database
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