The Boeing 727 is a mid-size, narrow-body, three-engine commercial jet airliner. It first took to the skies in 1963 and was, for a very long time, the most popular jet-liner in the world. 1,831 727s were delivered. The 727's sales record for the most jets bought in history was broken in the early 1990s by its sister, the Boeing 737. In August 2006, a total of 127 Boeing 727-100 aircraft and 493 Boeing 727-200 aircraft remain in airline service.
The Boeing 737 is the world's most popular medium to long range, narrow body commercial passenger jet aircraft. With over 6,000 ordered and over 5,000 delivered, it is the most ordered and produced commercial jet airliner of all time and has been continuously manufactured by Boeing since 1967. The 737 is now so widely used that at any given time, there are over 1,250 airborne worldwide. On average, one takes off or lands every five seconds.