The material imperfections generated by Additive Manufacturing (AM) processes across multiple scales can differ significantly from those arising by conventional manufacturing (CM) methods. To qualify these parts in a manner that accounts for all these imperfections without accounting explicitly for each of them, an outline of a rapid functional qualification methodology based on the concept of Performance Signature (PerSig) is presented first. The PerSigs are defined for both the prequalified CM parts and the AM-produced ones. Comparison measures are defined and enable the construction of differential PerSigs (dPerSig) in a manner that captures the differential performance of the AM part vs. the prequalified CM one. This approach is extended in this paper for the case of multiaxial loading conditions reflecting actual in-service loading. Application of the methodology is presented for a fitting bracket in the P-3C Orion aircraft platform and is based on synthetic data. The application of multiaxial loading emulating in-service loading conditions is proposed by the utilization of a custom-designed 6-DoF robotic testing system that will generate physical data.