Identification of aircraft critical loads envelope requires a lengthy and rigorous analysis procedure that includes simulating the aircraft at thousands of load cases identified in the certification requirements. Imposing a Global Finite Element Model (GFEM) in this process is computationally very expensive, hence, Reduced Order Models (ROM) of airframes are commonly employed in the static and dynamic aeroelasticity load analyses. This thesis presents two high fidelity ROM methodologies, one based on Hybrid Stick Model (HSM) approach and other, Optimized Stick Model (OSM), based on stick model optimization to match a set of eigenvalues and eigenvectors of GFEM. A case study is employed where the HSM and OSM along with the conventional Stick Model (SM) are employed in the dynamic aeroelasticity loads analyses of a Bombardier aircraft platform. Results obtained show that the HSM and OSM have superior dynamic characteristics compared to the conventional SM.