This paper illustrates in the context of the operational requirements for a business aircraft, the dependence of airframe design and powerplant choice on aerodynamics.The Handley Page Jetstream twin turboprop airplane at 12, 500 lb A.U.W. is used to illustrate this thesis. Performance and layout of executive and high-density versions, 300 mph cruising, stage ranges up to 2000 miles, payload up to 18 passengers and 2 crew, and low first and running costs, are covered.Among subjects discussed in detail are: 1. Choice of wing area, planform and t/c ratio. 2. Choice of engines and propellers. 3. Modification of wing section to improve flow near trailing edge. 4. Tunnel tests to eliminate hysteresis with double slotted flap. 5. Tail unit design.The powerplant, Turbomeca Astazou XIV and Hamilton Standard propeller, is described. The direct control of propeller blade angle, characteristic of the Astazou, is shown to simplify piloting and increase safety.