Trijet passenger aircraft manufactured by Boeing
, and the successor to the Boeing 707
. Its main competition was the two-engined Douglas DC-9
. Once, the 727 was the best-selling jet in the world: that title now belongs to the Boeing 737
It has three engines because that was the best compromise its designers could make. United Airlines wanted a four-engine airplane for high-altitude takeoffs out of Denver. American Airlines wanted a two-engine airplane similar to today's Boeing 757. Eastern Airlines wanted a three-engine airplane for the Caribbean. Boeing decided to give it three to make everyone happy.
The middle engine on the 727 is actually located inside the rear end of the fuselage: it uses an S-shaped duct to bring air in from an intake on the tail fin. This design feature was later used on the Lockheed Tristar.