An aircraft propulsion system has an engine assembly having an axis of rotation, a fan assembly operatively connected to the engine assembly and comprising a plurality of fan blades arranged circumferentially around the axis of rotation and a monolithic nacelle assembly which circumferentially encloses the fan assembly. The propulsion system has a ratio of fan assembly outer diameter to nacelle assembly outer diameter of at least 0.87. As a result, the propulsion system provides for a significantly larger fan assembly outer diameter for a given nacelle assembly outer diameter than a conventional prior art turbofan engine, thereby increasing the specific power output or the bypass ratio of the propulsion system, which will result in improved propulsive efficiency without an increase in nacelle drag.