A mapping of fatigue crack growth rates in thick plates of a high strength aluminium alloy has been done. The plate thicknesses investigated was 100, 150 and 200 mm. In this work, material from near edge at near surface and mid-thickness has been investigated. Measurements of crack length has been performed using DC potential drop. Cyclic condensation is used in order to reveal crack growth behaviour for stage I and the earlier part of stage II crack growth. Influence of crack closure, crack branching and slow growing side cracks on fatigue crack growth rate of S-L and L-T oriented specimens are discussed. Variation of difference in growth rate in the upper part of the stage II growth between near surface and mid thickness positioned L-T specimens are found to vary with plate thickness.