Many services have a complex network infrastructure (transport, Internet, etc.). Disruptions caused by accidents or weather conditions can paralyze traffic for a long time. But how to improve the robustness of networks? This robustness improvement would reduce the time of exposure to disruptions and their impact on overall traffic. Lots of studies have been done on identifying critical links and nodes but not so many analyze the paths. In this paper, we propose a new method to measure network robustness based on alternative paths. Beyond improving the French low-cost flight network robustness by 15%, the method attempts to show the relevance of analyzing network vulnerability from a path-based approach.