The paper includes some ideas of approaching phenomena of occurrence of aircraft inefficiencies in a new way, a new definition of the failure state, as well as two methods of analysing the aircraft failure states. The first one finds its application to an object in operation (Method of Object in Operation - MOE /Polish abbr./), whereas the second one - to an object under design (Method of Object under Design - MOP /Polish abbr./). Analytical relationships have been given, ones that describe probability of the aircraft failure state to occur, for both the methods. These are followed with examples of how to use both the methods in technical applications in the Polish Air Force.