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 (
Serpentine shape). 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. Currently, the
Dassault Falcon 7X and
Dassault Falcon 900 business jets, and the
Tupolev Tu-154M narrow-body airliner in limited production, are the only aircraft in production that use the S-duct design.