S-duct

thumb|The central engine on the Tupolev Tu-154|Tu-154 is fed through an S-duct thumb|S-duct geometry

An S-duct (or serpentine inlet) is a type of jet engine intake duct used in several types of trijet aircraft. In this configuration, the intake is in the upper rear center of the aircraft, above or below the stabilizer, while the exhaust and engine is at the rear of the aircraft. The S-duct is located in the tail, or empennage, of the aircraft. The shape of the S-duct is distinctive and easily recognized, and was used in several aircraft, beginning in 1962 with the Hawker Siddeley Trident. The Dassault Falcon 8X and Dassault Falcon 900 business jets are the only aircraft in production that use the S-duct design.