The choice of the design point of an engine is the result of market studies, as well as negotiations with the airframe manufacturer and the subsequent operators (launching customers) .Press must be defined, which is the basis for the interpretation of accounting and the lifetime determination an average mission. It is based primarily on the intended use of the aircraft mission (see Figure 2.30), but not necessarily be a point of the mission. In commercial aircraft, the average is about Mission at cruise altitude of 10 km on a standard day.