Flight simulation fatigue crack propagation tests were carried out on 2024-T3, 7475-T761 and mill annealed Ti-6A1-4V sheet in thicknesses up to 3 nim and representative for traJisport aircraft lower wing skin stiffened panels of end load capacities 1.5 and 3 MN/m. There was a significant effect of sheet thickness on crack propagation. Thinner gauge materials exhibited slower crack propagation mainly because of greater retardation of crack growth after severe flights. The relevance of the results for the choice of advanced structural concepts and materials is discussed, and a recommendation for further investigation is given.