WPR24LA084

Bearing degradation that increased clearances between the bearing and crankshaft journal surfaces, resulting in fatigue cracks and the subsequent failure of the No. 3 connecting rod and a total loss of engine power. Contributing to the accident was the mechanics and owner/operator’s continued operation of an engine that exceeded the manufacturers’ recommended overhaul.

The flight instructor reported that, shortly after departing the airport, the engine oil pressure indication dropped to near zero. The instructor intended to turn back to the departure airport, but the engine exhibited an uncommanded reduction of power. The instructor then attempted to land at another airport but the engine lost all power. The instructor initiated a forced landing in a residential area, striking a tree and colliding with an unoccupied vehicle, which caused substantial damage to the airplane. Postaccident examination of the engine revealed that the Nos. 3 and 4 connecting rods had separated from the crankshaft. The No. 3 connecting rod fractured at two locations on the strap due to multiple fatigue cracks that initiated at the outer surface next to the connecting rod bolt heads. The fracture of the No. 4 connecting rod strap and all four connecting rod bolts from the Nos. 3 and 4 connecting rods was secondary to the failure of the No. 3 connecting rod, which likely encountered elevated cyclic stress due to degradation of the No. 3 bearing. Heat tinting on the interior surfaces of the No. 3 connecting rod strap pieces and heat damage and circumferential scoring on the No. 3 connecting rod journal indicate bearing issues preceding the fatigue failure of the connecting rod. As the No. 3 bearing degraded, higher stresses likely developed in the connecting rod strap and cap due to increased clearances between the bearing and the crankshaft journal surfaces, leading to fatigue crack initiation and growth in the connecting rod strap. Fracture surfaces on the No. 3 connecting rod cap also showed signs of high cyclic stress, likely associated with the No. 3 bearing issues. The No. 4 bearing also showed signs of excessive wear. The worn bearing condition was likely associated with excessive service time. Similarly, the No. 3 bearing failure was likely associated with the excessive engine operating time since new. Maintenance records revealed that the engine total time since new was 3,745.6 hours since it was installed on the airplane about 44 years prior to the accident. No records of an engine overhaul were found in the supplied maintenance records. Lycoming Service Instruction No. 1009BE recommends that the accident engine model should be overhauled within 12 calendar years of the date it first entered service or the date of its last overhaul, or after 2,000 operating hours from the last overhaul.

On February 10, 2024, at 0745 mountain standard time, a Cessna 172P airplane, N52436, was substantially damaged when it was involved in an accident near Goodyear, Arizona. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor reported that, shortly after departing Glendale Airport (GEU), Glendale, Arizona, and during their climb to the practice area, she noticed the engine oil pressure indication had dropped to near zero. The flight instructor took control of the airplane and requested to return to GEU for a precautionary landing. Before making the 180° turn back to GEU, an uncommanded reduction of power occurred and she decided to land at Phoenix Goodyear Airport (GYR), Goodyear, Arizona. About 2 miles from GYR and about 1,000 ft above ground level, the engine lost total power. The instructor searched for an alternative place to land, put the airplane in a slip, and force-landed on a street in a residential area, clipping a tree and colliding with an unoccupied truck in the process. The airplane sustained substantial damage to the fuselage and both wings. Postaccident examination of the wreckage revealed that the engine remained attached to the engine mounting assembly. The crankcase had a crack near the No. 4 cylinder mount at the 12 o’clock position. The cylinder rocker covers were removed, and the cylinder overhead components were dark in color and covered with residual oil. The cylinders were examined with a lighted borescope, which revealed that the combustion chambers were undamaged and had a normal amount of combustion deposits. The crankshaft had limited rotation and cylinder overhead components moved normally during the limited rotation. Piston Nos. 3 and 4 did not move during the crankshaft rotation. The accessory tachometer drive and both magnetos rotated during the crankshaft rotation. Magneto to engine timing was found at 25° before top dead center of the No. 1 cylinder. Both magnetos remained secure on their respective mounting pads. The No. 4 cylinder was removed to facilitate further examination. It revealed that the No. 4 connecting rod was separated from the crankshaft with mechanical damage to the yoke (strap) end. The lower yoke portion was separated from the connecting rod. The crankshaft No. 4 connecting rod journal surface showed normal operating signatures. The No. 3 connecting rod was separated from the crankshaft journal and had mechanical damage to the yoke end. Both yoke end portions separated from the connecting rod. The No. 3 connecting rod journal surface showed thermal distress and mechanical damage. The separated connecting rod parts were found in the crankcase bay area between cylinder Nos. 3 and 4. The No. 4 bearing was found with deformation and no thermal distress. Four connecting rod cap bolt ends separated about mid-length and all 4 nuts remained attached to the bolts. The No. 2 cylinder was removed and the connecting rod was found loose on the crankshaft. The connecting rod showed thermal distress at the yoke and cap end. The majority of the bearing separated from the connecting rod. The No. 2 connecting rod journal showed thermal distress. The No. 1 cylinder and connecting rod were removed and the connecting rod journal surface showed normal operating signatures. The connecting rod nuts were found tightly secured on the Nos.1 and 2 rod caps before removal. The Nos. 3 and 4 connecting rod parts were sent to the NTSB Materials Laboratory for further examination. The four connecting rod bolts for the two connecting rods had irregular fractures on slant planes with deformation consistent with ductile overstress fracture. The strap fracture on the No. 4 connecting rod showed matte gray fracture features on a portion of the fracture surface and smearing damage on the remainder, also consistent with ductile overstress fracture. Fracture surfaces on the cap pieces were examined and generally showed rough features consistent with ductile overstress fracture. Portions of the fracture had somewhat smoother features with curving boundaries, consistent with progressive fracture. However, the surfaces were relatively rough and represented a small portion of the cross-section consistent with relatively high cyclic stress levels. The No. 3 connecting rod strap undamaged portions of the fracture surface had relatively smooth fractures with curving crack arrest lines, features consistent with fatigue. Radially-oriented ratchet marks were also observed, consistent with multiple fatigue origins. The oil filter was removed from the engine and disassembled. Metal contamination consistent with bearing material was noted in the pleats of the filter. The oil suction screen was removed and contained metal contamination. The screen was about half full of metal consistent with bearing material. The oil sump was removed and contained bearing material fragments. The maintenance records revealed that the last annual inspection was performed January 26, 2024, with a total airframe time of 3,764.1 hours. The engine total time since new read 3,745.6 hours. The airplane had 55.2 hours of operation since the last inspection. On August 18, 2023, about 589 hours before the accident flight, the No. 4 cylinder assembly was replaced with a new cylinder assembly kit. The engine was shipped from Lycoming’s factory in November 1980, and installed on the airplane, which was manufactured in 1980. The supplied maintenance records did not indicate any evidence of a subsequent overhaul. Lycoming Service Instruction No. 1009BE recommends the following: CALENDAR TIME PERIOD TBO All engine models are to be overhauled within twelve (12) calendar years of the date they first entered service or of last overhaul. This calendar year time period TBO is to mitigate engine deterioration that occurs with age, including corrosion of metallic components and degradation of non-metallic components such as gaskets, seals, flexible hoses and fuel pump diaphragms. OPERATING HOUR TIME PERIOD TBO For the accident engine, the instruction recommends an operating hour time between overhaul period of 2,000 hours. It states, “These TBOs are to mitigate engine deterioration that occurs during normal operation such as wear and high cycle fatigue of metallic components.”