Failure Analysis of Crashed Helicopter Main Components

Abstract

Many helicopter accidents are due to complications regarding flight operations, ground duties (mission planning and preparation), training and instructions. These are significant concerns within the existing global policies for momentously dropping the number of accidents in the years to come. Nevertheless, when accidents occur the successive investigations should include non-destructive inspection, for clarifications to eliminate possible causes like material defects, component and systems failures, and design deficiencies. To elucidate this, the present paper summarizes observations of non-destructive inspection (NDI) for clarifications regarding mechanics of fracture. Based on the results of visual, hardness, fractography, metallography, magnetic particle, x-ray radiographic, ultrasonic thickness and x-ray fluorescence observations, it is concluded that major components/assemblies of the crashed helicopter exhibited dynamic fracture modes consistent with failure due to overstress without any signs of slow stable fatigue crack growth. The non-destructive inspection observations have indicated no contribution of corrosion, stress-corrosion-cracking or any material deficiency toward final failure of examined components. The tail rotor control rod exhibited a typical triaxial-stress-state impact loading failure. The triaxial stress state was induced at the junction of inside reinforcement and the hollow rod making it the weakest site against impact or a dynamic stress condition.