Safety of aerospace structures must be ensured by robust procedures and methods of nondestructive testing. To fulfill such requirements, different NDT techniques are needed according to diverse physical conditions and types of defects in aerospace structures. Based on level of loading on each part and the life time of the component, a regularly scheduled maintenance is critical for inspection of aerospace components. However, to optimize the inspection schedule in terms of time and cost and to be able to cover as many types of the defects and/or different parts in each round of inspection, considering the techniques in what is called testing group and defect/part families can optimize the inspection schedule. Similar concepts have been extensively used in machining variety of parts with different machines in manufacturing industries. In this paper, Principal Component Analysis (PCA) has been used for classifying the NDT techniques required for inspection of defects in an aerospace structures testing plan. The presented method shows how the classification technique can be used for inspection planning and testing schedule for aerospace structures.