Background Information.

In the early 1970s Boeing began considering further developments of its narrow-body 727 trijet. Designed for short and medium length routes the Boeing 727 was the best-selling commercial 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 727 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 since the launch of the 727.

United Airlines provided input for the proposed 727-300, which Boeing was poised to launch in late 1975, but lost interest after examining the development studies of the 7N7. Although the 727-300 was offered to Braniff Internationl Airways and other carriers, customer interest remained insufficient for further development. Instead, airlines were drawn to the high-bypass-ration turbofan engines, new flight deck technologies, lower weight, improved aerodynamics and the 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 passengers, and a 7N7-200 with seating for over 180 passengers. New features included a redesigned wing, under-wing engines, and lighter materials, while the forward fuselage, cockpit layout, and T-tail configuration which was 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 totalling 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, later versions of the 737s later fulfilled this requirement.

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 1973. Design targets included a 20 percent reduction in fuel consumption from new engines, plus 10 percent from aerodynamic improvements. Lighter materials and new wings were also expected to improve efficiency. The maximum tak-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 take-off 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. 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. CAD (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 for greater commonality with the 767. Cathode-ray tube (CRT) color displays replaced conventional electromechanical instruments, with increased automation, thus eliminating the flight engineer position common to three-person cockpits. After completing a short conversion course, pilots rated on the 757 could be qualified to fly the 767 and vice versa, owing to their design similarities.
A new aft-loaded shape, which produced lift across most of the upper wing surface, instead of a narrow band as in previous airfoil designs, was used for the 757's wings. The more efficient wings had less drag and greater fuel capacity, and were similar in configuration to those on the 767. The wider wingspan produced less lift-induced drag, while the larger wing roots increased undercarriage storage space and provided room for future stretched versions of the aircraft.

One of the last 727 vestiges, the T-tail, was dropped in mid-1979 in favor of a conventional tail. This avoided the risk of an aerodynamic condition known as a deep-stall, and allowed for more passengers to be carried in a less tapered rear fuselage. At 155.3 feet (47.3 m) in length, the 757-200 was 2.1 feet (0.640 m) longer than the 727-200, and with a greater proportion of its internal volume devoted to cabin space, seating was available for 239 passengers, or 50 more than its predecessor. The fuselage cross-section, whose upper lobe was common to the 707 and 737, was the only major structural feature to be retained from the 727. This was mainly to reduce drag, and while a wider fuselage had been considered, Boeing's market research found low cargo capacity needs and reduced passenger preference for wide-body aircraft on short-haul routes.

Boeing built a final assembly line in Washington at its Renton factory, home of 707, 727, and 737 production, to produce the 757. Early in the development program, Boeing, British Airways and Rolls-Royce unsuccessfully lobbied the British aircraft industry to manufacture 757 wings. Ultimately, about half of the aircraft's components, including the wings, nose section, and empennage were produced in-house at Boeing facilities with the remainder subcontracted to primarily U.S.-based companies. Fairchild Aircraft manufactued the leading-edge slats, Grumman Aerospace supplied the flaps and Rockwell International produced the main fuselage. Production ramp-up for the new narrow-body airliner coincided with the winding-down of the 727 program with final assembly of the first aircraft beginning in January 1981.

The prototype 757 was rolled out of the Renton factory on January 13, 1982. The aircraft, equipped with RB211-535C engines, completed its maiden flight one week ahead of schedule on February 19, 1982. The first flight was affected by an engine stall, following indications of low oil pressure. After checking system diagnostics, the company test pilot John Armstrong and co-pilot Lew Wallick were able to restart the affected engine and the flight proceeded normally thereafter. Subsequently, the 757 embarked on a seven-day weekly flight test schedule. By this time Boeing had received 136 orders from seven carriers.
The seven-month 757 flight test program used the first five aircraft built. Tasks included flight systems and propulsion tests, hot and cold weather trials, and route-proving flights.

Data from the 767 program helped expedite the process. After design issues were identified, the 757's exit doors received dual-spring mechanisms for easier operation, and the fuselage was strengthened for greater bird strike resistance. The production aircraft was 3,600 pounds (1,630 kg) lighter than originally specified, and recorded a three percent better-than-expected rate of fuel burn. This resulted in a range increase of 200 nautical miles (370 km), and prompted Boeing to tout the aircraft's fuel efficiency characteristics. After 1,380 flight test hours, the RB211-powered 757 received U. S. Federal Aviation Administration (FAA) certification on December 21, 1982. This was followed by UK Civil Aviation Authority (CAA) certification on January 14, 1983. The first delivery to launch customer Eastern Air Lines occurred on December 22, 1982, about four months after the first 767 deliveries. The first 757 with PW2037 engines rolled out about one year later, and was delivered to Delta Air Lines on November 05, 1984.

Eastern Air Lines operated the first commercial 757 flight on January 01, 1983, on the Atlanta-to-Tampa route. On February 09, 1983, British Airways began using the aircraft for London-to-Belfast shuttle services, replacing the Hawker Siddeley Trident 3B trijets. Charter carriers Monarch Airlines and Air Europe also began 757 operations later that year. Early operators noted improved reliability and quieter performance compared with previous jetliners. Transition courses eased pilots' introduction to the new CRT-based cockpit, and no major technical issues arose. Eastern Air Lines, the first 727 operator to take delivery of 757s, confirmed that the aircraft had greater payload capability than its predecessor, along with lower operating costs through improved fuel burn and the use of a two-crew member flight deck. Compared with the 707 and 727, the new twinjet consumed 42 and 40 percent less fuel per seat, respectively, on typical medium-haul flights.