This paper presents a new technique for generating linear fractional transformation based uncertainty models for use in the robustness analysis of flight control systems using the structured singular value μ. The proposed approach does not require closed-form linear expressions for the aircraft dynamics - only a non-linear software model of the closed loop aircraft, which can be efficiently trimmed and linearized numerically, is required. The capability of the proposed approach to identify worst-case uncertain parameter combinations is demonstrated. The approach is compared with classical analysis methods via the robustness analysis of a control law for a Boeing 747 transport aircraft.