The authors investigated the behavior of a model gas turbine combustor with respect to flame flashback due to combustion-induced vortex breakdown (CIVB). This is a very complex mechanism of interaction between the swirling flow and the flame. The phenomenon has been observed both experimentally and numerically. The experimental rig allows observation of the flame using simultaneously the PIV and LIF of the flashback. Because the CIVB is a highly unsteady process, Large-Eddy Simulation was applied to achieve a very detailed view at the flow field during the flashback. The combustion of a perfectly premixed methane-air mixture was modeled using an analytic expression for the flame surface density. Stability limits have been determined with simulations and experiments for the whole operating range of the burner. Furthermore, the detailed data allow a very close look at the flashback process in all its stages.