Primary finding
Probable cause
The failure of maintenance personnel to properly assemble the engine's accessory gearbox, which resulted in a total loss of engine power due to partial blockage of the main oil passage by an o-ring. The blockage reduced oil flow to the turbine shafting, which led to the total failure of the gas producer turbine shaft and the power (free) turbine shaft. A factor was the lack of suitable terrain for the forced landing.