Generalized Engine Inoperative Performance Requirements for Future Aircraft Concepts

Future transport aircraft concepts leveraging advanced propulsion systems enable more efficient flight, but face major certification barriers prior to entering service. One critical barrier is the poor applicability of "one engine inoperative" (OEI) performance requirements defined in FAA Part 25 and EASA CS-25 regulations that only apply to transport aircraft designed with 2-4 homogeneously sized gas turbine engines, making direct application to heterogeneous and distributed propulsion systems ambiguous. This work constructs generalized OEI performance requirements anchored to existing regulations and are parameterized by the specific excess power lost during a propulsion system failure, maintaining broad applicability to any aircraft and propulsion system architecture. Under the same parameterization, an "engine inoperative correction factor" is also constructed to scale the propulsion system size, enabling seamless integration into the aircraft sizing process. Both contributions are utilized to size a notional Elysian E9X, revealing system-level performance penalties for configurations sized under 4-, 5-, and 6-engine inoperative failure modes. The power loading decreases by up to 28%, thus increasing the aircraft's maximum takeoff weight and battery energy stored onboard by up to 17% and 19%, respectively. Additional operational constraints prevent attaining system-level benefits for less severe propulsion system failure modes.