NTSB Identification: NYC99IA056.
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Incident occurred Friday, February 05, 1999 in LEXINGTON, KY
Probable Cause Approval Date: 11/22/2000
Aircraft: Piper PA42-1000, registration: N37KW
Injuries: 2 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

The during descent for landing, the airplane's right engine, a TPE331-14B, experienced an uncontained gearcase failure. Disassembly of the engine revealed that the gearcase was ruptured in the 1st bull gear's plane of rotation and that the 1st bull gear had a 90 degree arc of the rim and gear teeth separated. Metallurgical examination of the 1st bull gear revealed a fatigue fracture that had originated in the gear's bore splines. The fatigue originated in area where the spline thickness was significantly reduced by indentations on the pressure surface of the splines. Review of the engine's overhaul manual revealed a tie-rod was used to provide a clamping force between the spur gear and 1st bull gear. The assembly procedures required that the tie-rod be stretched with a load of 22,000 pounds, and then secured with a nut that was hand-tightened. During disassembly of the gearcase, it was not possible to determine the amount of stretch on the tie-rod, or the breakaway torque on the retaining nut. Maintenance records revealed that the gearcase was disassembled, and reassembled during repairs, which were performed by engine manufacturer.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

Improper assembly of the engine gearcase by the manufacturer, which resulted in an uncontained failure of the 1st bull gear.

Full narrative available

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