ATL05LA052

While approaching Moncks Corner Airport to land, the airplane's engine seized and the pilot was forced to land on tree tops about 400 feet from the runway. Post-accident examination of the engine assembly revealed four fatigue cracks on the planetary carrier housing that propagated outboard and caused the housing to fracture into multiple pieces. The teeth around the sun gear in the area that corresponds to the planetary gears were fractured and exhibited deformation. The teeth of the planetary gears showed deformation. The splined lock was examined and exhibited fretting damage. The width of the fretting/galling damage on the four flat surfaces was wider compared to the thickness of the mating square slot on the cap, consistent with lateral movement between the splined lock and cap. All spine teeth on the splined lock showed deformation. Dimensional inspection of the gears were performed on the engine approximately 98 hours prior to the accident. At that time, a new sun gear was installed in the engine. The mating four planetary gears were not replaced and not required to be replaced. Uneven wear between gear faces caused stresses to be distributed unevenly between the gears, resulting in accelerated wear of the gears. Wear of the planetary gears are required to be evaluated when the engine is overhauled, but there is no record of a recent engine overhaul.

On February 23, 2005, at 1719 eastern standard time, a WSK PZL Mielec M-18A, N2296Y, registered to AG Aviation Equipment LLC, and operated by the commercial pilot, collided with trees during a forced landing in Macedonia, South Carolina. The agricultural flight was operated under the provision of Title 14 CFR Part 137, and visual flight rules. Visual meteorological conditions prevailed and no flight plan was filed. The pilot was not injured and the airplane sustained substantial damage. The flight originated in Moncks Corner, South Carolina on February 23, 2005, at 1650.

According to the pilot, he had completed his last swath run and, was returning to the Moncks Corner Airport. The airplane was set at cruise power when the pilot stated that the engine lost power without any warning. The pilot attempted to make the runway but collided with and rested in trees tops about 400 feet short of the runway. The pilot was able to egress and climb down the tree without injury.

The post-accident examination of the airplane revealed the left and right wings were separated from the fuselage, both wings exhibited circular crush damage. The fuselage came to rest on trees and the propeller blades exhibited damage. Fire damage to the starter governor was also noted.

Post accident examination of the propeller assembly revealed that the propellers would not rotate by hand. When efforts to rotate the propeller assembly failed, the nose cone and diaphragm were removed, which revealed damage to the planetary housing. Laboratory examination of the planetary carrier housing, performed by the NTSB Material Laboratory Division, revealed multiple cracks that propagated outboard and caused the housing to fracture into multiple pieces. The teeth around the sun gear in the area that corresponds to the planetary gears were fractured and exhibited deformation. The planetary gear exhibited damage on the teeth, particularly near the crowns of the teeth. Deformed particles of metal were found on the surface of the gear teeth. Metallurgical examination of both gears showed no evidence of material anomalies. The composition and hardness of the carrier housing, sun and planetary gears were within the limits or exceeded the minimum values specified by the manufacturer. No anomalies were found in the microstructure of the housing. The splined locks were examined and exhibited fretting. All spine teeth on the splined locks showed deformation.

Maintenance and inspection criteria for the engine are addressed in Honeywell Service Bulletin (SB) TPE 331-72-0180, ENGINE- Service Life Limits of Critical Life Components and Periodic Maintenance Schedules, revision 31, issued November 07, 2003, specifies a Continued Airworthiness Maintenance (CAM) program for agricultural operators. Dimensional inspection of the gears is specified at CAM, and this gear inspection was performed on the engine approximately 98 hours prior to the accident. At that time, a new sun gear was installed in the engine. The mating four planetary gears were not replaced and are not required to be replaced. According to Honeywell Service Bulletin TPE331-72-0180, wear of the planetary gears are required to be evaluated when the engine is overhauled, but there is no record of a recent overhaul of the engine.

On September 1, 2004, the tachometer time at the last CAM inspection was 4470.9 hours. Current tachometer time could not be obtained due to cockpit damage. Wear of the planetary gears are required to be evaluated when the engine is overhauled, but there is no record of a recent overhaul of the engine.