Based on constant amplitude fatigue tests on 12 mm thick plates, in a 2024 T351 aluminum alloy, a previous study has shown that the spatial distribution of predominant facies reflects the effects of stress intensity factor and the load ratio. In this paper, this technique is applied to constant amplitude crack propagation tests to thin plates of the same material, and it is shown that the quantitative fracture surface analysis method developed permits to distinguish the effects of fracture mechanics parameters. Results obtained under variable amplitude tests are then analyzed. The fracture surface analysis permits the identification of a change in fracture mode and accurate life evaluation can then be made after taking into account the observed change. In the case of an aluminum lithium alloy this method cannot be directly applied due to changes in fracture mechanisms under variable amplitude loading. But an analysis is carried out by taking into account associated changes in crack closure levels, which leads to excellent life predictions under variable amplitude test conditions.