The nondestructive detection of fatigue cracks at fastener holes in aircraft structures employing guided waves is studied. Experimentally the first antisymmetric Lamb wave mode A0is excited using piezoelectric transducers and the scattered field is measured by means of a heterodyne laser interferometer. The detectability of small defects is investigated and quantified by a parameter study at a model system and using finite difference calculations. The main influence is found to be the ratio of wavelength and defect size. Measurements employing shorter wavelength Rayleigh waves show the predicted good detectability of a small quarter‐elliptical fatigue crack. © 2003 American Institute of Physics