The investigation identified stress corrosion as the principal propagation mode of axial cracking up to about 8 inches axial extent in the shanks of three propeller blades. Logbook records implied that cracking occurred during time periods of several months or more during which the blades were either off-wing or idle while on-wing. Stress corrosion cracks initiated from corrosion pitting on the surface of an internal taper bore cavity followed by intergranular corrosion that penetrated the thickness of a compressively stressed layer produced by shot peening. Pitting was promoted by galvanic action between the aluminum blade material and a tapered aluminum bronze bushing inserted into the free end of the taper bore. Hoop stresses in the blade shank resulting from the interference fit of the bushing and quenching residual stresses resulting from blade heat treatment were presumed to be drivers of stress corrosion crack growth. These matters are being pursued further in a stress measurement and stress corrosion testing crack initiation and propagation test program ongoing at this time. No material or process deficiencies relative to manufacturing specifications were identified as causal to the incidence of cracking. The occurrence of axial cracking per se does not impair blade function; however, propagation into the blade retention fillet can induce circumferential fatigue cracking as did occur in two of the three blades investigated. The blades were removed from service before fatigue cracking propagated to critical sizes.