This Book is based on conceptual Design of A 150 seater jet airplane cruising at M = 0.8, at 11 km altitude and having a gross still air range(GSAR) of 4000 km is considered$. The presentation is divided into eight sections - Data collection - Preliminary weight estimation - Optimization of wing loading and thrust loading - Wing design - Fuselage design, preliminary design of tail surface and preliminary layout - c.g. calculations - Revised estimates of areas of horizontal and vertical tails - Features of designed airplane - Details of performance estimation