Methods are provided forming a metallic nacelle inlet structure for a turbine engine aircraft propulsion system with an axis. The nacelle inlet structure includes an inlet lip portion and an outer barrel portion. One of the method may include steps of: forming the inlet lip portion; forming the outer barrel portion; arranging the inlet lip portion axially adjacent the outer barrel portion; and friction stir welding the inlet lip portion to the outer barrel portion to provide a circumferentially extending weld joint between the inlet lip portion and the outer barrel portion.