An aircraft crashed following the loss of yaw control in full airborne flight. The subsequent discovery of broken shutter bolts in the rear pitch reaction control valve led to an inspection campaign that found bolt failures of a similar nature in valves on several other aircraft. The bolts were removed and analyzed to determine the mode and cause of failure. Based on the results of macroscopy, scanning electron fractography, metallographic examination, and chemical analysis, the failures were caused by stress corrosion cracking, and in one case, overtightening.

The quill shaft in an aircraft engine was found in two pieces following a flameout. One piece was short, straight, and otherwise undamaged; the other piece was bent in several places as was the sleeve that covered it. The facture surface, as viewed under optical and scanning electron microscopes, was flat and shiny with deformation marks and dimples, typical of torsional overload, and signs of severe rubbing on the periphery. Based on their observations, investigators concluded that the quill shaft failed by torsional overload, the source of which could not be determined.

This chapter discusses the failure of a first-stage compressor blade in an aircraft engine and explains how investigators determined that it was caused by fatigue, with a crack originating from corrosion pits that developed in the root transition region on the convex side of the airfoil.

This chapter provides an overview of the tools and techniques used to examine failure specimens and the wealth of information that can be obtained from fracture surfaces, cracks, wear patterns, and other such features. It discusses the use of metallography, fractography, and optical and electron microscopy. It presents a number of images recorded using these methods and explains what they reveal about the mode of fracture and the state of the component prior to failure.

This chapter describes an investigation following an aircraft accident in which the main undercarriage struts had failed. Visual examination revealed that the starboard strut fractured about 13 cm from the end nearest the underside of the wing. A close-up view of the fracture surface indicated that cracking initiated at the outer periphery of the strut and propagated inward until overload fracture occurred. SEM imaging revealed fatigue striations along the outer periphery and dimples elsewhere, indicative of tensile overload. Based on these observations, investigators concluded that the starboard strut failed by fatigue, which overloaded the port side strut as evidenced by its slant type fracture pattern.

This chapter provides an overview of the various inspection methods used with metals and alloys, namely visual inspection, coordinate measuring machines, machine vision, hardness testing, tensile testing, chemical analysis, metallography, and nondestructive testing. The nondestructive testing methods discussed are liquid penetrant inspection, magnetic particle inspection, eddy current inspection, radiographic inspection, and ultrasonic testing.

This chapter discusses the practices and procedures used to reveal and record macrostructural features such as hardening depth, weld thickness, crack size, porosity, hot folds, and machining and tooling marks. It provides information on sectioning, sample location, orientation, surface grinding, and etching. It describes macrographic etchants and the features they reveal along with common etching problems and how to avoid them. It explains how to evaluate etching results and how they can be improved using remedial processes such as light grinding. It also discusses photographic reproduction, lighting, and image enhancement techniques.