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The fatigue crack propagation behavior of new generation Al alloys developed foraeronautical applications depends on alloy composition, aging condition and atmosphereenvironment. The crack path and the growth rate at moderate DK and in the near-thresholddomain are governed by the slip morphology. In absence of environment assistance, a stage Ilikeregime with slow growth rates is produced for shareable precipitates or solute clusterstructures that promote heterogeneous slip band formation and (111) faceted cracking in Al-Li-Cu alloys and underaged Al-Cu-Mg alloys, in contrast with a ductile transgranular featurelessstage II crack path in overaged Al-Cu-Mg. In air, water vapor assistance induces a transgranularstage II regime associated to homogeneous slip generating a flat-facet and step-like features forall materials; an adsorption assisted propagation mechanism is assumed to prevail at moderateDK in both Li and Mg bearing materials and in the near-threshold domain for Al-Cu-Mg alloysin contrast to hydrogen assistance for Al-Cu-Li alloys at low growth rates.