Dekalb, IL, USA
N512JA
AUMAN JL T-51
The experimental amateur-built airplane experienced a total loss of engine power during a phase one test flight. The pilot performed a forced landing on a field where airplane nosed-over due to the rough condition of the field that precluded a normal landing rollout. Before the phase 1 test flight, the pilot had returned the engine to the kit manufacturer for repair due to leaking engine coolant. Postaccident examination of the engine revealed catastrophic damage; the engine head bolt had been tighten above the engine manufacturer's torque values, which indicated that the kit manufacturer used excessive torque on the head bolts in an attempt to repair coolant leakage through the engine head. The postaccident examination showed that the engine was assembled with cast and not forged pistons, which should be used in high performance applications. The bending and thread damage on the intact connecting rod bolt for the forward right cylinder and the mating thread damage in the connecting rod were consistent with the bolt backing out until it sheared the remaining threads. Another bolt that backed out of position was also present on the connecting rod in the middle right position. Measurements of cylinder wall carbon lines showed a variance in size, which may have been due to hydraulic lock related bending of the connecting rods.
On December 11, 2012, about 1545 central standard time, an Auman JL T-51, N512JA, experimental amateur-built airplane experienced a total loss of engine power after takeoff from De Kalb Taylor Municipal Airport (DKB), De Kalb, Illinois. The pilot performed a forced landing to a field. The airplane nosed over and impacted terrain during the landing. The airplane sustained substantial damage to the fuselage and vertical stabilizer. The airline transport pilot sustained serious injuries. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a test flight. Visual meteorological conditions prevailed and a flight plan had not been filed for the local flight that was originating at the time of the accident. The pilot, who was also the aircraft builder, stated that he installed the engine onto the airframe and noticed that it was leaking engine coolant before it had been initially run. About three weeks later, the pilot removed the engine and shipped it to Titan. The pilot stated that Titan had told him that the engine head bolts were improperly torqued. The engine was returned and was reinstalled onto the airframe. During the phase one test flight, the engine, which had accumulated about 25 hours since overhaul, began to "studder" during a departure climb from DKB. The engine oil pressure was 60-65 psi and the engine operating temperatures were in the "normal" range. The pilot performed a landing on a plowed agricultural field where the airplane nosed over after rolling about 30 feet. Post-accident examination of the engine (Honda J35 A6, serial number 1430792A3L329203Z LL53240) showed that the engine sustained catastrophic damage. There was no evidence of detonation. During the removal of the head bolts with a torque wrench, the head bolt torques values were in the range of 120-130 ft-lbs. The specified torque value for the cylinder head bolts for the engine was 72.3 ft-lbs. The examination also revealed that all of the connecting rods were bent. Black colored lines consistent with carbon lines were present around the top circumference of all the cylinder walls. The depths of these lines were as follows: right front cylinder – 2 mm, right middle – 5 mm, right rear – 5 mm, left front – 2 mm, left middle – 5 mm, left rear – 2mm. Material laboratory examination of piston pieces from the forward left and middle right cylinders revealed that all fracture features were consistent with overstress fracture. A piece of the piston from the forward left position has a microstructure consistent with a cast aluminum alloy. The examination also revealed the connecting rod from the forward right position was fractured in the "I" section. The cap was also fractured, and approximately 2/3 of the cap was missing. Fracture features and deformation in the "I" section of the connecting rod showed features consistent with overstress fracture under bending loads. The fracture features of the cap were substantially damaged by post-fracture impacts, but remaining areas of the fracture showed relatively rough features consistent with overstress fracture. One of the connecting rod bolts was fractured at a slant angle consistent with overstress fracture. The mating side of the bolt remained within the connecting rod strap. The longer connecting rod bolt appeared to be intact, but was bent. The shank was uniformly bent along most of its length, but a sharper bend occurred approximately ½ inch from the end in the threaded end of the bolt. The threads in the bolt appeared largely flattened, and impact damage was observed all around the head and shank. Thread damage was observed in the connecting rod hole corresponding to the position of the intact connecting rod bolt. The threads in the end of the hole closest to the split line had damaged thread peaks. The thread damage was observed along approximately ½ the length of the hole, and the remaining threads furthest from the split line appeared intact. Images from the engine teardown were also reviewed during the Materials Laboratory examination. A view of the connecting rod from the middle right position showed a portion of the connecting rod bolt shank is visible in the image. According to the president of Titan Aircraft, the engine on the accident airplane was a 2003 or 2006 Honda J35-A6 engine. There is "very little" that is modified on the engine. The modifications include the cooling system and governor. All of the engine parts are Honda parts. The engines are bought used and anything that exceeds new engine specifications is replaced. The engine parts that are replaced include: pistons, piston rings, valves, and bearings. Following an engine rebuilt, engine runs are "normally" not performed after an engine is built, but Titan Aircraft "occasionally" will perform an engine run of an engine that is built. The National Transportation Safety Board Investigator-In-Charge (IIC) invited Titan Aircraft to attend the engine examination. Titan Aircraft stated that they would not attend but would be available to answer questions. The IIC invited Titan Aircraft to be a party to the investigation, but Titan Aircraft did not accept the invitation. The IIC did not receive requested build records for the engine, which Titan Aircraft said were available and agreed to provide those records.
The improper engine overhaul by the airplane kit manufacturer, which resulted in a catastrophic engine failure.
Source: NTSB Aviation Accident Database
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