The fighter jet success can be determined by many factors – its performance, sales, arm load capacity, maneuverability and combat effectiveness, But a jet has to be accepted into service first by approved by respective aerospace firm like FAA, DGCI. Thus, it is only natural that the most unsuccessful fighter jets are the ones that never left the drawing board or went beyond the prototype stage. Of course, many potentially successful jets do not enter production because of economic, political, or other non-aviation-related reasons. For example many late Soviet projects did not see mass production due to budgetary reasons after the collapse of the Soviet Union: the supersonic VTOL Yak-41 and Mikoyan’s fifth-generation attempt, the 1.44, among them. Those are not failures – they are results of changing situation around the project To be considered a failure, the jet has to fail because of its design or manufacturing defects or not able to withstand the varying atmospheric conditions. But