A design study was performed for an advanced subsonic transport having a payload of 150 passengers and a 2500 NMi range with maximum payload. The development of the baseline aircraft is explained with attention to geometric constraints, design for growth, operational requirements, and interior layout. Computer modeling was performed using a new version of AirCraft SYNThesis (ACSYNT) which includes: an integrated beam structural analysis method for the wing and fuselage; NASA Engine Performance Program (NEPP) for propulsion cycle and weights analysis; and Aircraft Life Cycle Cost Analysis (ALCCA) for manufacturing and operations cost and cash flow analyses. All programs are incorporated within ACSYNT to permit optimization of the input parameters, with either aircraft gross weight or design mission direct operating cost as a figure of merit. In addition, sensitivity studies of the best design are presented for wing aspect ratio and engine design point bypass ratio.