The Boeing 737 is a short to medium range, single aisle, narrow body jet airliner. Originally developed as a shorter, lower cost twin engine airliner derived from Boeing’s 707 and 727, the 737 has nine variants, from the early -100 to the most recent and largest, the -900. Series -600 through -900 are still being produced.

First envisioned in 1964, the 737 entered service in 1968. Forty years later it has become the most ordered and produced commercial passenger jet in the world. It is Boeing’s last surviving narrow-body airliner currently in production, sometimes serving markets previously filled by 707, 727, 757, DC-9 and MD-80/90 airliners. The 737 has been continuously manufactured by Boeing since 1967 with over 8,000 ordered and 5,857 delivered as of 2008. There are over 1,250 737s airborne at any given time, with one departing or landing somewhere every five seconds on average.