The 5,000th 737, a 737-700, came off the production line on Feb. 13, 2006. Guinness World Records has acknowledged the 737 as the most-produced large commercial jet airplane in aviation history. With more than 4,100 airplanes in service, the 737 represents more than a quarter of the total worldwide fleet of large commercial jets flying today. More than 541 operators fly 737s into more than 1,200 cities in 190 countries. It is estimated that approximately 1,250 737s are in the air at any given moment, with one taking off or landing every 4.6 seconds. After the wings and landing gear are joined to the fuselage, the airplane moves to the moving assebly line for final assembly.