WPR24LA159

The partial loss of engine power during cruise flight due to the improper installation of the master connecting rod main bushing set screws, which backed off and allowed the main bushing to shift, resulting in scoring damage on the crankshaft that led to the initiation of a fatigue crack and separation of the forward crankshaft.

The pilot reported that he was conducting a formation flight with another airplane when the engine began making “clicking” and “banging” sounds, surging in speed, and losing power. The pilot attempted to troubleshoot the partial loss of engine power but was unsuccessful. Unable to maintain altitude, the pilot performed a forced landing at a closed gliderport but was unable to stop the airplane on the runway. During the landing sequence, the airplane subsequently crossed over a road and struck an unoccupied camper and the ground, sustaining substantial damage to the left wing and engine mount.  A postaccident examination of the engine revealed that the crankshaft front section was separated (fractured through) at the master connecting rod journal and crankpin areas. The crankshaft fracture surfaces showed features consistent with a fatigue fracture initiating from an area of substantial scoring damage on the journal radius. The master rod main bushing (bearing) was found rotated within its pressed fitting about 90° from its original position and also showed substantial scoring damage and wear. The two main bushing set screws (which held the master rod main bearing in place) were not present and were not identified during the examination. Based on the mechanical damage and deformation observed on the main bushing set screw holes, the forward side of the main bushing edge (positioned nearest to the journal radius), and the connecting rod ends near the set screw areas, the set screws likely loosened and backed out, then remained in the small cavity between the connecting rod ends and the master rod until they sustained enough mechanical deformation to exit the area. The main bushing set screw holes showed three installation chiseled strike marks each, indicating that the main bushing was likely previously replaced two times on the master rod. It is likely that the set screws were not properly installed with the appropriate strike marks, which allowed them to loosen.

On May 21, 2024, about 1220 mountain standard time, a Nanchang China CJ-6A airplane, N4182C, sustained substantial damage when it was involved in an accident near Peoria, Arizona. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed Deer Valley Airport (DVT), Phoenix, Arizona, and flew northwest toward Lake Pleasant to practice formation flying with another airplane. While in cruise flight, the engine began making “clicking” and “banging” sounds, surging in speed, and losing power. The pilot attempted to troubleshoot the partial loss of engine power but was unsuccessful. Unable to maintain altitude, he located a closed gliderport with a turf runway, extended the landing gear and flaps, and performed a few S-turns to lose altitude and align with the runway. The pilot stated that the airplane touched down about halfway down the runway, bounced on the uneven terrain, then became airborne again as he pulled up to avoid a road at the end of the runway. The airplane subsequently struck an unoccupied camper and the ground, collapsing the nosewheel landing gear and sustaining substantial damage to the left wing and engine mount.  Postaccident examination of the engine revealed evidence of mechanical damage on various engine interior surfaces, and metal debris was present in the oil pump signaling filter. The crankshaft front section was separated (fractured through) at the master connecting rod journal and crankpin areas. The crankshaft fracture surface showed ratcheting and beach marks consistent with a fatigue fracture originating from an area of substantial scoring damage on the journal radius and extending over most of the surface area. The master rod main bushing was found rotated within its pressed fitting about 90° from its original position and showed wear and scoring on its interior surface. The two main bushing set screws were not present in the set screw holes and were not identified during the examination. The forward side of the main bushing edge (positioned nearest to the adjacent journal radius) and the connecting rod ends near the set screw holes had mechanical damage and deformation. The set screw holes were mechanically damaged and deformed, and each hole showed three chiseled installation strike marks (see figures 1 and 2). (Typically, during assembly of this type of engine, the master rod main bushing is pressed into the large end of the rod and is kept in place by two set screws. The set screws are locked in place on the master rod by chiseled strike marks near the set screw heads to prevent the screws from loosening.) Figure 1. Master rod main bushing set screw hole and installation strike marks. Figure 2. Master rod main bushing set screw hole and installation strike marks. The airplane’s maintenance records revealed that the engine was installed on the airplane on January 13, 2019, with 300 hours of time in service. The last airframe and engine condition inspections were performed April 5, 2024, at an engine time of 568.51 hours and a total airframe time of 2,100.2 hours. At the time of the accident, the airplane had accrued about 6 hours since the inspection.