ERA12LA422

The pilot was conducting a formation flight when the airplane’s engine experienced a loss of power. The pilot and his instructor then conducted a forced landing to a runway and landed long, with the airplane departing the surface and coming to rest in a field. Post accident examination revealed that the number three piston connecting rod cap separated from the piston connecting rod when the hardware came loose and the connecting rod disconnected during flight. Maintenance records showed that the engine had been overhauled several years prior to the accident. It is likely that the mechanic did not properly install the connecting rod bolts and nuts, which resulted in the number three piston connecting rod disconnecting during flight, and subsequent loss of engine power.

According to the Lycoming Service Instruction No. 1458F, the stretch length for the connecting rod bolts must be 2.255/2.256 inches. Review of the maintenance records for the airplane showed that the last engine overhaul was completed on August 5, 2005, at a tachometer time of 3,266.0. The tachometer time at the accident was 3,938.0. The engine had accrued 672 hours since the overhaul. No additional maintenance requiring installation of the connecting rods was noted. On June 28, 2012, about 1147 central daylight time, a Mooney, M20J, N174JB, registered to and operated by an individual, collided with terrain during a forced landing at Houston County Airport (M93), McKinnon, Tennessee. The certified flight instructor (CFI) and private pilot received minor injuries, and the airplane sustained substantial damage. Visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 91, instructional flight. The flight originated from M93 at 1100. The CFI submitted a written statement. The purpose of the flight was to practice formation flying and the CFI was instructing the pilot in formation flying procedures. The two-airplane formation made an approach to runway 26 for a formation landing. The CFI noted they were not in a safe position to land, and elected to make a go around. The lead airplane landed and rolled to the end. As they completed the crosswind to downwind maneuver, the engine continued to run, “…at perhaps 10 percent power.” The private pilot radioed that the engine was smoking and the CFI took control of the airplane. He attempted to land midfield on runway 08. Visibility became limited due to oil on the windscreen, and vibration made airspeed reading difficult. The landing was long and with excessive speed, resulting in the overrun of the runway. While traveling on the grass, the CFI noted trees ahead and to the right. He made a slight left turn, contacting the perimeter road’s berm. The airplane bounced, became airborne, and came to rest in a grassy area across the road. An examination of the airplane revealed that the nose gear separated, and the firewall and the empennage sustained substantial damage. The engine crankcase top halves were cracked. The Lycoming IO-360-A3B6D engine was examined. External inspection of the crankcase showed a crack radiating vertically from the bottom of the case mating surface to the top mating surface. Removal of the oil pan identified the bottom half of the number three piston rod, rod bearing cap, bearings, parts of the crankcase, two piston rod bearing cap bolts, and three rod bearing cap nuts. Due to damage, the piston and upper part of the broken rod could not be removed from the cylinder. The number four cylinder was removed from the crankcase with difficulty due to extensive damage to the cylinder skirt and crankcase. The number one cylinder was removed from the crankcase. The piston sustained impact damage to the bottom of the skirt and one pistonrod bearing cap nut was missing. The bolt was still in place. The number two cylinder was removed from the crankcase, and both rod bearing cap bolts were in place with nuts attached.