Event Description
During the climb phase of flight, the engine experienced shaking, rattling, and a loss of power. The flight instructor assumed control of the aircraft and executed an emergency off-airport landing. During the rollout on the ground, the aircraft sustained substantial damage to the leading edges and lower surfaces of both wings.
Maintenance History
The engine had been previously inspected in accordance with TCM 99-3, a mandatory service bulletin that required the removal of the No. 1 and No. 3 cylinders. During reassembly of these cylinders, three snap rings on the crankshaft counterweights at the No. 2 and No. 5 cheeks were reinstalled. An inspection of the No. 5 cheek revealed that these three snap rings were not fully seated.
Mechanical Findings
Examination of the crankshaft and counterweight showed signatures consistent with a counterweight striking the crankshaft. According to the investigation, this condition can only occur if the counterweight pin is not in place. A revision to TCM mandatory service bulletin 99-3C, published on July 27, 1999, now requires that the gap between the snap ring ears be measured to ensure they are properly seated during reassembly.