Boeing 737-100

The 737-100 was the first variant of the Boeing 737 and the smallest member of the whole family. It grew out of Boeing's studies for a short-haul jet that would supplement the 727 on short and thin routes. Preliminary design work began on May 11, 1964, based on research that indicated a market for a fifty to sixty passenger airliner flying routes of 50 to 1,000 miles (100 to 1,600 km).

The initial concept had podded engines on the aft fuselage, a T-tail as on the 727 and five-abreast seating. Engineer Joe Sutter moved the engines to the wings, which lightened the structure and made six-abreast seating easier to accommodate. The nacelles were mounted directly to the underside of the wings without pylons, so the landing gear could be shortened and the fuselage lowered, improving passenger and baggage access; with the aft fuselage freed, the horizontal stabilizer could be attached to it instead of being carried on a T-tail.

Boeing was far behind its competitors: the Caravelle had been in service since 1955, and the BAC One-Eleven, Douglas DC-9 and Fokker F28 were already in flight certification. To save time the 737 reused 60% of the structure and systems of the 727, notably the 148-inch (3.76 m) wide fuselage cross-section inherited from the 707, which allowed six-abreast seating against the rivals' five. The chosen engine was the Pratt & Whitney JT8D-1 low-bypass turbofan, delivering 14,500 pounds-force (64 kN) of thrust. Chief project engineer Jack Steiner presented the design in October 1964 at the Air Transport Association maintenance and engineering conference, where its elaborate high-lift devices raised concerns over maintenance costs and dispatch reliability.

The Boeing board approved the launch on February 1, 1965. Lufthansa became launch customer on February 19, 1965, with an order for 21 aircraft, after Boeing assured the airline that the project would not be cancelled; consultation with Lufthansa over the previous winter had raised the seating capacity to 100. When United Airlines asked in April 1965 for a slightly larger aircraft, the stretched version became the 737-200 and the original short-body aircraft the 737-100; detailed design continued on both simultaneously.

The first -100 was rolled out on January 17, 1967, and made its maiden flight on April 9, 1967, flown by Brien Wygle and Lew Wallick. The FAA issued Type Certificate A16WE on December 15, 1967; it was the first aircraft to include approval for Category II approaches as part of its initial certification. Lufthansa received its first aircraft on December 28, 1967, and on February 10, 1968, became the first non-American airline to launch a new Boeing aircraft. In 1968 the unit cost was US$3.6 million.

The original thrust reversers, taken from the 727's outboard nacelles, proved relatively ineffective and tended to lift the aircraft off the runway when deployed, reducing the load on the main wheels and the effectiveness of the brakes. In 1968 an improvement was introduced: a 48-inch (120 cm) tailpipe extension and new target-style reversers, with the doors set 35 degrees from the vertical to deflect the exhaust over and under the wings. The change became standard after March 1969 and was offered as a retrofit for aircraft in service. Longer nacelle and wing fairings, improved airflow over the flaps and slats and a flap system allowing greater use during takeoff and landing followed, together raising payload and range and improving short-field performance.

The 737-100 was largely overshadowed by its bigger sibling, the 737-200, which entered service two months later and was widely preferred by airlines. Lufthansa was the only significant customer and only 30 were built: 22 for Lufthansa, five for Malaysia–Singapore Airlines (MSA) and two for Avianca, the last delivered to MSA on October 31, 1969. The first and the last built were also the last in service. The prototype, registered N73700, went to NASA on July 26, 1973, which flew it as N515NA for 30 years until retiring it on September 27, 2003; it is now on static display at the Museum of Flight in Seattle and is the last surviving example of the type. The last one built, sold to MSA and later to Air Florida, served for 23 years as a VIP aircraft of the Mexican Air Force under registration TP-03 and was broken up in 2006.