ERA23FA025

The airplane was in cruise flight about 5,400 ft when the pilot declared an emergency due to a partial loss of engine power. The pilot and controller discussed options for the forced landing, but ultimately the pilot announced that the engine was “stopped,” and that the airplane was “heading down.” A witness described the airplane maneuvering about 75 ft above the ground before it impacted wires, crossed the road on which he was driving, and came to rest in trees on the opposite side of the road. He reported that there was no engine noise and that the airplane made only a “whistling” sound. After the airplane came to rest suspended in trees, the witness watched as it caught fire, “shifted,” then fell from the trees before it exploded and became engulfed in flames. Examination of the engine at the accident site revealed that the crankshaft could not be rotated by hand, and the oil suction screen was completely occluded with debris that comprised metallic particles and pieces of rubber material consistent in appearance with pieces of rubber magneto drive cushion (bumper). Further examination revealed that the crankshaft was fractured at the rear edge of the No. 6 connecting rod journal. The No. 6 connecting rod and rod cap were damaged, and the No. 6 rod bearing was extruded. Review of maintenance records indicated that the engine underwent a field overhaul about 10 years before the accident, during which the crankshaft was replaced. At the time of the accident, the engine had accrued about 101 hours since overhaul. Examination of the crankshaft fracture revealed a fatigue crack that initiated at the surface in the fillet radius between the No. 6 connecting rod journal and the forward cheek. Similar fatigue cracks were observed at the forward end of the connecting rod journal with features consistent with excessive loads induced during contact between the connecting rods and the engine case. The No. 6 rod bearing was likely destroyed due to interruption of the oil to the bearing from fatigue crack propagation. The crankshaft was made obsolete 30 years before the engine’s most recent overhaul, and although it was still authorized for use in multiple variants within this series of engines, it was not authorized for use in the accident engine model. Additionally, the connecting rod bearings installed on the accident engine were not authorized for use in the accident engine model. It is likely that the use of a crankshaft that was not approved for use in the accident engine make and model resulted in abnormal contact between the connecting rods and their journals, imparting stress to the crankshaft and resulting in its failure. It is possible that the renitriding of the crankshaft may have affected its ability to tolerate high loading and contributed to the failure. The observed nitride layer was thicker than the original specification, and the core hardness was lower than the specification. Combined, these factors increased the potential to generatecracks. While the oil filter screen was occluded with material consistent with a magneto bumper, there was no evidence of general oil starvation elsewhere within the engine, which would be consistent with an occluded screen; therefore, it is likely that the magneto bumper dropped into the engine due to large vibrations following the crankshaft failure, and broken pieces then became trapped in the oil screen. Further examination revealed that the connecting rod in the number 4 position was labeled 3, and the one in the number 3 position was labeled 4. Although this likely did not contribute to the accident, it is another indication of improper maintenance practices.

According to FAA and maintenance records, the airplane was manufactured in 1969 and was powered by a Lycoming IO-540-K1A5, 300-horsepower engine. The airplane’s most recent annual inspection was completed October 4, 2022, at 3,623.3 total aircraft hours. The engine underwent a field overhaul on October 1, 2012, and had accrued 101.5 total hours since that date. On October 18, 2022, at 0741 central daylight time, a Piper PA-32-300, N600JG, was destroyed when it was involved in an accident near Brentwood, Tennessee. The private pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the operator of a maintenance facility at the pilot’s home airport, the purpose of the flight was to deliver the airplane to Fayetteville Municipal Airport (YFM), Fayetteville, Tennessee, for an avionics repair. Automatic dependent surveillance - broadcast (ADS-B) data revealed that the airplane departed Springfield Robertson County Airport (M91), Springfield, Tennessee, about 0717 for YFM. Air traffic control communication information revealed that, at 0733:40, the airplane was in cruise flight about 5,400 ft mean sea level (msl) heading 180° at 139 knots (kts) groundspeed when the pilot declared an emergency due to a partial loss of engine power. The pilot and controller discussed options for the forced landing and agreed that Nashville International Airport (BNA), Nashville, Tennessee, was the closest option after the controller issued the pilot a heading of 350°. The controller subsequently instructed the pilot to turn to 030°, and at 0735:50, with the airplane about 4,800 ft at 109 kts groundspeed, the pilot reported to the controller that he could maintain altitude. At 0736:45, the airplane was about 4,500 ft, at 108 kts, when the controller advised the pilot that BNA was 11 miles ahead at his 11 o’clock position and instructed him to proceed to runway 2L, which the pilot acknowledged. At 0738:25, the airplane was about 3,500 ft travelling 94 kts when the pilot announced that the engine was “stopped” and that the airplane was “heading down.” The airplane continued its northeasterly heading for about 45 seconds until it entered a left descending turn from an altitude about 2,700 ft and groundspeed of 71 kts. The final plot depicted the airplane at 800 ft heading 205° at a groundspeed of 88 kts about 1,800 ft north of the accident site, which was located at an elevation about 730 ft. During the turn, the airplane’s groundspeeds varied between 63 and 88 kts. In a written statement, a witness described the airplane maneuvering about 75 ft above the ground before it impacted wires, crossed the road on which he was driving, and came to rest in trees on the opposite side of the road. He reported to a Federal Aviation Administration (FAA) inspector that there was no engine noise and that the airplane made only a “whistling” sound. The witness said that he parked his truck and called 911. Afterhe exited the truck, he saw fire “come from the plane” before he heard it “shift” in the trees and then fall to the street, where it “exploded” and became engulfed in flames. Local emergency services personnel secured the residential street, and the wreckage was examined the following day. The autopsy was performed by the Office of the Medical Examiner, Nashville, Tennessee. The cause of death was “blunt force injuries and thermal burns.” The FAA Forensic Sciences Laboratory performed toxicological testing on the pilot. The antihistamine cetirizine (116 ng/mL, ng/g) was detected in blood and (2286 ng/mL, ng/g) was detected in urine. At 0753, the weather reported at BNA, 7 miles southwest of the accident site, included wind from 310° at 5 knots, 10 miles visibility, and few clouds at 5,000 ft above ground level. The temperature was 3°C, the dew point temperature was -6°C, and the altimeter was 30.06 inches of mercury (inHg). The pilot held a private pilot certificate with ratings for airplane single-engine land and instrument airplane. He completed the requirements for operation under BasicMed on October 21, 2021, and he declared 480 total hours of flight experience on that date. The pilot’s logbook was not recovered, but his total flight experience was estimated at 505 hours based on the time accrued on the airplane in the year before the accident. The crankshaft, connecting rod assemblies, No. 6 piston and cylinder assemblies, main and connecting rod bearings, bags of debris collected from the oil sump, and the oil screen, front oil seal, and exemplar magneto bumpers were all examined by the NTSB Chief Technical Advisor-Materials, in Washington, DC. Examination revealed that the crankshaft was fractured through the No. 6 connecting rod journal adjacent to the forward cheek. The No. 6 connecting rod was fractured in the beam section near the small end. The big end of the No. 6 connecting rod was separated from the crankshaft but remained intact. The remaining connecting rods were intact and were attached to the crankshaft, rotating freely on their respective journals. Markings on the side of the crankshaft flange read “LW 10842 M06M 03P S166505-2,” indicating that it was Lycoming part number LW-10842, serial number S166505-2, with main journal diameters that had been ground 0.006-inch undersize and connecting rod journal diameters that had been ground 0.003-inch undersize. According to engine manufacturer representatives, crankshaft LW-10842 was made obsolete in 1979. Crankshaft LW-10842 and crankshafts that superseded part number LW-10842 were certified for use in multiple variants of the IO-540 series engines, including the -AA1A5, -K1C5, -K1F5, -K1J5, and -S1A5, but the list of certified variants did not include the accident engine model, IO-540-K1A5. The interior and exterior surfaces of the main bearings are shown in figure 1, labeled M1 through M5. The bearings were marked as FAA parts manufacturer approval (PMA) bearings with a partnumber that was consistent with the accident engine using a crankshaft with 0.006-inch undersize main journal diameters. The babbitt material on the interior surfaces of the bearings was intact with isolated debris and circumferential drag marks (comet tails). Coked oil deposits were present on the engine case contact surfaces on the back face of bearing M5 and on the oil channel surfaces on the back face of bearing M4. The edges of the oil channel holes were deformed on bearings M4 and M5, as indicated with arrows in the lower image in figure 3, consistent with contact with corresponding dowels in the engine case. The deformation was located at the aft sides of the holes on bearing M4 and the forward sides of the holes in bearing M5. Figure 1. Views of the main bearing interior (upper image) and exterior (lower image) surfaces. Arrows in the lower image indicate elongation at the edges of the oil supply holes. The crankshaft fracture surface revealed a fatigue crack that initiated at the surface in the fillet radius between the No. 6 connecting rod journal and the forward cheek. Similar cracks were observed at the forward end of the connecting rod journal with features consistent with excessive loads induced during contact between the connecting rods and the engine case. Evidence of sliding contact damage was observed on each of the cheeks at the forward and aft sides of the connecting rod journals. Corresponding rub marks were observed on the sides of the connecting rod assemblies. On the crankshaft, the heaviest contact damage was generally located where the cheek transitioned to the adjacent connecting rod or main journal. On the connecting rod assemblies, the heaviest rub contact was generally located at the middle of the arc for the cap and was associated with local heat tinting. Local heat tinting and sliding contact damage was also observed on the No. 1 connecting rod cap that remained assembled on the crankshaft. Sliding contact damage was also observed on the outer surfaces of the connecting rod caps. Although the No. 6 connecting rod cap exhibited more extensive contact damage, similar areas of sliding contact damage were observed on the No. 3 connecting rod cap. The damaged areas were stained dark with coked oil, which generally appeared darker in these areas relative to other areas of contact damage. While the oil filter screen was occluded with material consistent with a magneto bumper, there was no evidence of general oil starvation consistent with an occluded screen. The signatures of localized oil starvation at the No. 6 connecting rod bearing were consistent with oil interruption from fatigue crack propagation. During the field engine overhaul in October 2012, the crankshaft was replaced, and the replacement crankshaft installed in the engine had been renitrided. Examination revealed that the case depth was greater and the core hardness lower than that specified in the engineering drawings for that crankshaft. Furtherexamination revealed that, while the connecting rod bearings were eligible for use in multiple variants of Lycoming IO-540 series engines, the list did not include the accident engine, and that the connecting rod in the No. 4 position was labeled 3, and the one in the No. 3 position was labeled 4. The outer surfaces of the connecting rods showed evidence of contact with the engine case. The initial impact point was in power lines about 50 ft above the ground. The wreckage path was oriented on a magnetic heading about 180° and was about 60 ft in length; all major components of the airplane were accounted for at the scene. The fuselage came to rest upright in the street, rolled partially onto its right side, with the engine and propeller still attached. The propeller blades were largely intact. One blade displayed bending consistent with impact damage. The cockpit, cabin area, and the tailcone were consumed by post-crash fire. The empennage was fire-damaged but mostly intact. The tail section remained largely intact and was suspended in a tree about 45 ft above the fuselage, along with the left wing and left main landing gear. The components in the trees also displayed fire damage. The wings displayed impact damage consistent with collision with trees and terrain. Flight control cable continuity was confirmed from the cockpit to the flight control surfaces through several breaks consistent with impact and thermal damage. The engine displayed thermal damage, but only minor impact damage. It was separated from the airframe and examined at the scene. Attempts to rotate the propeller to establish continuity through the powertrain to the valvetrain and the accessory section were unsuccessful. The rear-mounted engine accessories were removed, then the engine accessory case was removed, and the crankshaft still could not be rotated by hand. The oil suction screen was removed and completely occluded with debris. The debris comprised metallic particles and pieces of rubber material consistent in appearance with pieces of rubber magneto drive cushion. Cylinder Nos. 1, 2, 3, 4, and 5 were removed. The pistons bore markings consistent with an aftermarket manufacturer. Damage to the No. 6 cylinder connecting rod and the No. 6 crankshaft rod journal was observed. The No. 6 cylinder was removed using a heavy hammer and prybars. The No. 6 piston remained in the No. 6 cylinder, which was not removed due to cylinder barrel skirt damage. The engine crankcase halves were separated. The crankshaft was fractured at the rear edge of the No. 6 rod journal. The No. 6 rod and rod cap were damaged, and the No. 6 rod bearing was extruded. The crankshaft main bearings bore markings consistent with bearings from an aftermarket manufacturer. No damage to the camshaft or cam followers was observed. No damage to the pistons or valves of cylinder Nos. 1, 2, 3, 4 and 5 was observed. Rusted areas were observed on the interior cylinder walls of all six cylinders.