A propulsion system for an aircraft including a plurality of primary engines is provided. The plurality of primary engines includes at least a first primary engine and a second primary engine, each configured for mounting to a respective one of a pair of wings of the aircraft. The propulsion system additionally includes an aft engine configured for mounting at a tail section of the aircraft. The plurality of primary engines are sized to provide an amount of thrust sufficient for the aircraft to takeoff without use of the aft engine, such that the aft engine may be configured as a non-prime reliable engine.