Aircraft structural fatigue life prediction has important military significance and the conspicuous economic value. In development phase fatigue life of flight vehicles is generally predicted based on some historic / assumed data which may differ significantly from the actual operational usage of the vehicle. Consequently, the fatigue life of an aircraft may reduce / increase. The service fatigue life of a structure depends on both the irregular amplitude load conditions and the assumptions during fatigue test. To find the actual fatigue life of a structure we need to subject the structure in laboratory with constant / variable amplitude loadings that should be representative of actual flight loads and at the same time in a form that can be applied conveniently in the laboratory. In case of uniform loading it is easy to find the number of cycles but the real service loads are normally irregular, so defining spectrum from flight data is quite difficult which corresponds to the actual random loads applying on the aircraft.In this research study, a simple methodology is proposed to extract fatigue loads spectrum from a typical flight tests data. It involves statistical analysis of flight data, data filtering, power spectral density (PSD), averaging and data reduction for generating a representative fatigue spectrum from experimental as well as actual flight data. The derived spectrum following this approach contains information of not only the number of occurrences of each load factors but also the fluctuating loads and corresponding exposure time for each occurrence. This methodology is validated by developing a spectrum from known raw data and then same procedure is applied on original flight data to generate the flight fatigue spectrum. Statistical processing of good sample size (number of flights) provides a reasonably good representative fatigue spectrum of that particular flight vehicle type. Every flight fatigue spectrum can also be used for structural health monitoring / residual life estimation on flight to flight basis.