Most important problems during development of fatigue bench test technology of airframe components are imitation of real loading and analysis of parameters connecting with initiation and fatigue crack growth. The key features when it is necessary taking for decision are to choice criterions of fatigue crack growth estimation. Abilities of traditional non-destructive testing (NDT), which are used during bench research, are limited. In addition to the traditional NDT it is offered to use the method of acoustic emission (AE). The main undercarriage leg of the passenger aircraft is an object of research. During the bench tests the loads acting during the different flight cycle were imitated. The critical undercarriage elements were found during operation and previous tests. There are a spline hinge eye, a trunnion, and a piston rod of shock absorber. The fatigue cracks were grown from artificial and natural stress concentrators. The fatigue crack initiation and development are checked by traditional NDT methods periodically and by AE method continuously. It is shown that in all cases the development of a fatigue crack occurs irregularly where the periods of accelerated growth are followed by the periods of slowdown. The crack initiation and initial growth cannot be to indicate by traditional NDT. They are analyzed either by the fractal analysis or by the AE method. Traditional NDT may be only used in final stages of fatigue crack growth. Comparison of results of AE and other methods shows that total AE change are connected with fatigue crack development. As a result, the AE method may be used to indicate microcrack initiation as well as to found its transformation into state which may be dangerous for further operation. It is shown that α-criterion is effective to estimate different stages of crack kinetics.