The paper deals with the consequences of stoppage of fuel supply from one wing tank for stability and control of aircraft. It is shown that the counterbalancing of the weight of the blocked fuel causes the development of the additional moment about the transverse axis of the aircraft, which changes the loaded index at landing. It is pointed out that the intersection of the changed loaded index at landing and actual landing weight could be displaced out of the operating limits of the aircraft in the balance graph. The question is raised whether the manufacturers have considered the described stoppage in fuel supply when laying down the operating limits, i.e. has the adequate safety reserve been provided.