Definitions of binary p-set and binary -set functions are given. The use of these definitions allows for any unknown parameter, , of the model of fatigue failure of aircraft failure to provide the economical effectiveness of an airline under a limitation of the fatigue failure rate (FFR) and the limitation of any fatigue failure probability of (FFP) in a fleet of aircraft . The solution of the problem using theory of semi-Markov process with rewords is based on a result of an acceptance full-scale fatigue test of an aircraft structure. If the result of this test is not good enough then this new type of aircraft will not be used in a service. Previously the redesign of this project should be done. For this strategy there is a maximum of FFP and a maximum of FFR as a functions of unknown parameter, . This maximum can be limited by the use of the offered here procedure. Numerical examples are given.