Boeing 757

Development

Background

In the early 1970s, following the launch of the first wide-body airliner, the 747, Boeing began considering further developments of its narrow-body 727. Designed for short and medium length routes, the trijet was the best-selling jetliner of the 1960s and a mainstay of the U.S. domestic airline market. Studies focused on improving the 189-seat 727-200, the most successful variant. Two approaches were considered: a stretched 727 (to be designated 727-300), and an all-new aircraft code-named 7N7. The former was a cheaper derivative using the 727's existing technology and tail-mounted engine configuration, while the latter was a twin-engine aircraft which made use of new materials and improvements to propulsion technology which had become available in the civil aerospace industry.

United Airlines provided input for the proposed 727-300, which Boeing was poised to launch in late 1975, but lost interest after examining development studies for the 7N7. Although the 727-300 was offered to Braniff International Airways and other carriers, customer interest remained insufficient for further development. Instead, airlines were drawn to the high-bypass-ratio turbofan engines, new flight deck technologies, lower weight, improved aerodynamics, and reduced operating cost promised by the 7N7. These features were also included in a parallel development effort for a new mid-size wide-body airliner, code-named 7X7, which became the 767. Work on both proposals accelerated as a result of the airline industry upturn in the late 1970s.

By 1978, development studies focused on two variants: a 7N7-100 with seating for 160, and a 7N7-200 with room for over 180 seats. New features included a redesigned wing, under-wing engines, and lighter materials, while the forward fuselage, cockpit layout, and T-tail configuration were retained from the 727. Boeing planned for the aircraft to offer the lowest fuel burn per passenger-kilometer of any narrow-body airliner. On August 31, 1978, Eastern Air Lines and British Airways became the first carriers to publicly commit to the 7N7 when they announced launch orders totaling 40 aircraft for the 7N7-200 version. These orders were signed in March 1979, when Boeing officially designated the aircraft as the 757. The shorter 757-100 did not receive any orders and was dropped; 737s later fulfilled its envisioned role.

Design effort

The 757 was intended to be more capable and more efficient than the preceding 727. The focus on fuel efficiency reflected airline concerns over operating costs, which had grown amid rising oil prices during the Yom Kippur War of 1973. Design targets included a 20 percent reduction in fuel consumption from new engines, plus 10 percent from aerodynamic improvements, versus preceding aircraft. Lighter materials and new wings were also expected to improve efficiency. The maximum take-off weight (MTOW) was set at 220,000 pounds (99,800 kg), which was 10,000 pounds (4,540 kg) more than the 727. The 757's higher thrust-to-weight ratio allowed it to take off from short runways and serve airports in hot and high conditions with higher ambient temperatures and thinner air, offering better takeoff performance than that offered by competing aircraft. Competitors needed longer takeoff runs for these hot and high conditions. Boeing also offered options for higher payload capability.

The twin-engine configuration was chosen for greater fuel efficiency versus three- and four-engine designs. Launch customers Eastern Air Lines and British Airways selected the RB211-535C turbofan built by Rolls-Royce, which was capable of 37,400 pounds-force (166 kN) of thrust. This marked the first time that a Boeing airliner was launched with engines produced outside the U.S. Domestic manufacturer Pratt & Whitney subsequently offered the 38,200 pounds-force (170 kN) thrust PW2037, which Delta Air Lines launched with an order for 60 aircraft in November 1980. General Electric also offered its CF6-32 engine early in the program, but eventually abandoned its involvement due to insufficient demand.

As development progressed, the 757 increasingly departed from its 727 origins and adopted elements from the 767, which was several months ahead in development. To reduce risk and cost, Boeing combined design work on both twinjets, resulting in shared features such as interior fittings and handling characteristics. Computer-aided design, first applied on the 767, was used for over one-third of the 757's design drawings. In early 1979, a common two-crew member glass cockpit was adopted for the two aircraft, including shared instrumentation, avionics, and flight management systems. In October 1979 the nose was widened and dropped to reduce aerodynamic noise by six dB, to improve the flight deck view and to give more working area for the crew and for greater commonality with the 767. Cathode-ray tube (CRT) color displays replaced conventional electromechanical instruments, with increased automation eliminating the flight engineer position common to three-person cockpits.