CEN20LA123

The pilot and passenger were conducting a personal flight when the engine experienced a partial loss of power. The pilot was unable to maintain altitude and made a forced landing to a road. During the forced landing, while turning right to stay on the road, the airplane ground looped and collided with trees, sustaining substantial damage. Examination of the engine revealed that a portion of the No. 1 cylinder valve head was fractured due to the inward propagation of a radial rim fracture, and the initiation and propagation of a chordal fracture in the filet area perpendicular to the axis of the stem. The initial crack developed at the rim and propagated inward toward the center of the valve head as a radial rim crack. When the crack front reached the fillet region of the head, a second crack initiated and propagated in fatigue as a chordal fracture. A final overstress fracture occurred near the rim. This type of failure is likely due to cyclic uneven expansion and contraction stress cracks that propagate inward, as a result of inadequate valve seating. The engine maintenance records showed that a repaired No. 1 cylinder was installed on May 9, 2014. The partial maintenance release stated that the cylinder repair process included refaced valves and three angle cut valve seats. There were no other entries related to the No. 1 cylinder. The engine had accumulated about 598 hours since the cylinder was installed. Annual inspections were completed every year after this cylinder installation.

On March 14, 2020, about 1315 central daylight time, a Cessna 182 airplane, N20847, was substantially damaged when it was involved in an accident near Baxterville, Mississippi. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that about 10 minutes after departure and about 1,500 ft mean sea level, the engine experienced a “sudden reduction in power.” He reported that all instrument gauges appeared normal, and the engine was running smoothly, but it had a “different sound and didn’t have enough power to maintain altitude. While troubleshooting, he turned on the electric fuel pump and selected both the PRIME and ON positions; there was no change in engine performance. He completed a magneto check with only “a slight drop” per side. Since he was unable to maintain altitude, he attempted to divert to IH Bass Jr Memorial Airport (4R1), Lumberton, Mississippi, but continued to lose altitude. The pilot noted that the terrain in the area consisted of rolling hills and forest land. He selected a dirt road, which veered right, and was adjacent to a clear-cut field, for a forced landing. After landing and while trying to make the right turn to follow the road, the airplane ground looped and went backwards into a tree line. The airplane collided with numerous trees during the accident sequence and sustained substantial damage to the fuselage, empennage, and both wings. The tachometer time was 5,182.1 hours at the time of the accident. A postaccident examination of the engine revealed that a portion of the No. 1 cylinder intake valve head was missing, and the inside of the cylinder sustained impact damage. Figure 1 shows the inside of the cylinder and missing valve piece. The cylinder was removed from the engine and the intake valve was sent to the NTSB Materials Laboratory for metallographic examination. Figure 1. Inside of No. 1 Cylinder The metallographic examination revealed that the combustion face of the valve exhibited impact marks uniformly across the face. A portion of the valve head was fractured due to the inward propagation of a radial rim fracture, and the initiation and propagation of a chordal fracture in the filet area perpendicular to the axis of the stem. The initial crack developed at the rim and propagated inward toward the center of the valve head as a radial rim crack. When the crack front reached the fillet region of the head, a second crack initiated and propagated in fatigue as a chordal fracture. A final overstress fracture occurred near the rim. Adjacent to the keeper/collet groove, there were chafe marks around the circumference of the valve stem, which could be indicative of valve floating. Impact marks and rim damage on the valve seat were consistent with foreign object damage. The seat revealed impact wear scars and deformed machining marks. No indications of seat erosion were noted. A review of the engine maintenancerecords showed that a repaired No. 1 cylinder was installed on May 9, 2014, at tachometer time 4,584.1 hours. The partial maintenance release stated that the cylinder repair process included refaced valves and three angle cut valve seats. There were no other entries related to the No. 1 cylinder. Annual inspections were completed every year after this cylinder installation. Also, Nos. 2, 3, and 4 repaired cylinders were installed in 2015.