Abstract: n the structural reliability analysis one-sided tolerance limit X-KS is usually used hrthe lower limit of a normally distributed population X with unknown mean μand unknown standard deviation σ In the above expression k is called ont-sided tolerance limit factor and X and S are the sample estimates of μand σ,respectively. The tolerance interval(X-KS,+∞)is required to be such that the probability is equal to a preassigned valueγ(which is called confidenee) that the tolerance interval includes at least a given proportion Pof the population(which is called nominal survival probability).There is an important q uestion:what is the true survival probability a corresponding to the one-sided tolerance limil?In the present paper the formula for predictingois derived.From the numerical results,in some instances the true surviv- al probability a may be less than the nominal survival probability P. For example,when γ=90%,P=0.999 999,if the sample size n is less than 43 then α< P.In the aircraft or helicopter struc- tural reliability analysis the sample size n is usually much less than 43.Therefore,γ=90% and P=0.999 999 recommended in some literature are unreasonable.

Key words: reliability analysis, fatigue life, tolerances (mechanism)