On the full (large)-size (scale) Designs an area of fatigue damages’ concentration is considered as a pool of some Local Zones, which defines durability of total Design. The investigation of stochastic dependence of fatigue damages’ accumulation are carried out on samples with numerous concentrators as a model of solid body with embedded flaws or internal cracks. Under the assumpion that the fatigue damages’ accumulation happen dependent, the Hypothesis of Local Zones is proposed. On the basis of double exponential probability distribution of fatigue durability with logarithm scale of loading cycles, the four-parametrical mathematical model of Local Zone’s fatigue strength is developed. The model unites parameters of fatigue durability’s distribution function, a distribution function of endurance limits, linear-pieces S-N fatigue curve and a sensitivity threshold on cycles. It is supposed that piecewise and linear description of S-N fatigue curve with various degree “m” is connected with various mechanisms of fatigue damages’ accumulation in a material (design) body when loading level is changing. The existence of Local Zones postulates is shown on examples of the Bench Tests and Operation Work of full-size Designs. It is shown that the best method of nondestructive test for monitoring of Local Zones’ technical health is the method of acoustic emission. Controlled advancing destruction of the critical Local Zone, presented as indicator of degradation of total Design, will allow developing design methods by the principle Fail Safe Concept.