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Fatigue cracking of aircraft engine turbine components can initiate at metallurgical defects that were not detectable during post-manufacturing inspections. This paper presents the results obtained during the detailed metallurgical examination of turbine blades from recently completed accident investigations. The subject blades were examined in a scanning electron microscope operated in the topographic mode to pinpoint the location of the fatigue origins. Serial sectioning was then performed to characterize the blade microstructure at the suspected fatigue crack origins. In one case, a focused ion beam instrument was employed to examine several potential origins while minimizing damage to the rest of the fracture face. The fatigue crack origins were identified as casting-related defects. The conditions under which such defects could be detected using non destructive inspection techniques are discussed.