1The scattering of high frequency guided ultrasonic waves by a fatigue crack at the side of a 2 fastener hole has been studied. The guided wave pulse consists of the superposition of the two 3 fundamental Lamb modes A0 and S0 above the cut-off frequencies of the higher modes. The 4 scattered field was simulated using a three-dimensional finite difference algorithm with a 5 staggered, Cartesian grid for the limited area of interest around the hole and an analytical phase 6 angle correction for the additional, variable propagation distance. Experimentally, the modes 7were selectively excited using a standard ultrasonic wedge transducer and measured using a 8 laser interferometer, resulting in good spatial resolution. The scattered field was measured and 9 simulated for an undamaged hole, a small, part-thickness quarter-elliptical fatigue crack, and a 10 through-thickness fatigue crack. Good agreement was found and a significant influence of the 11 fatigue cracks on the scattered field was observed. The complex difference of the scattered 12 field due to additional scattered waves at the fatigue cracks of variable depth and length was 13 evaluated. This allows for the sensitivity prediction of high frequency guided waves for fatigue 14 crack detection at fastener holes, a significant maintenance problem for ageing aircraft. 15 16