The paper is a step towards the evaluation of the worst-case scenario caused by strong wind gusts impacting civil engineering air-inflated lightweight structures. These extreme events with short durations but high strengths are responsible for short-term highly instantaneous loads endangering the structural integrity. A generic test case is defined including a discrete wind gust model, the approaching turbulent boundary layer and a flexible structure. The simulation framework relies on a partitioned solver for FSI. To save CPU-time, a part of the investigations is conducted for the rigid case as a physical meta-model. The particularly critical cases were examined for the flexible structure. Under varying system parameters (gust strength, length and position) the objective functions (forces, deflections, inner stresses) are evaluated. The worst case occurs for maximal gust strength and length, when the gust hits the membrane at half height. Furthermore, the effect of the superposition of the gust with background turbulence is analyzed for two scenarios. The gust is first superimposed to different inflow turbulences of the same intensity leading to non-negligible deviations of forces and deflections. Second, the level of the turbulence intensity is increased showing only a minor effect on the structure not generating a new worst case.