The effects of flat to slant fracture transitions on flight simulation fatigue crack propagation in specimens of 7O5O aluminium alloy forgings are discussed. For specimens containing flat, shearlipped, or full slant fractures at similar crack lengths the crack resistance (R curve) approach appears to provide an explanation for differences in the static crack growth increments induced by peak loads. The results emphasize the complexity of fatigue under realastic loading and add another variable to environmental effects.