An aircraft passenger seat assembly as described herein is formed from two primary and modular components: a structural frame that provides passenger support and dynamic load paths for the seat assembly; and a comfort frame that provides the passenger seating surface and the external upholstery layer for the seat assembly. If the seat assembly is designed for multiple passengers, then a separate comfort frame is used for each passenger seat location. The structural frame can be formed as a molded composite construction, and the comfort frame can also utilize a molded composite support frame. The support frame is used as a mounting shell for a fabric carrier that includes the external upholstery layer. The modular design and use of composite materials results in a significant weight and parts count savings relative to conventional seat designs.