Boeing 707

The Boeing 707 is a mid-size, narrow-body four-engine jet airliner that was manufactured by Boeing Commercial Airplanes from 1958 to 1979. Its name is most commonly pronounced as "Seven Oh Seven". Versions of the aircraft have a capacity from 140 to 202 passengers and a range of 3,680 to 3,735 nautical miles (6,820 to 6,917 km). Developed as Boeing's first jet airliner, the 707 features a swept-wing design with podded engines. Dominating passenger air transport in the 1960s, and remaining common throughout the 1970s, the 707 is generally credited with ushering in the Jet Age.[4][5] Although it was not the first jetliner in service, the 707 was the first to be commercially successful. It established Boeing as one of the largest manufacturers of passenger aircraft, and led to the later series of aircraft with "7x7" designations. The subsequent 727, 737, and 757 also share elements of the 707's fuselage design.

The 707 was developed from the 367-80, a prototype jet aircraft which Boeing produced as a design study in 1954. A larger fuselage cross-section and other design modifications resulted in the initial production 707-120, powered by Pratt & Whitney JT3C turbojet engines, which first flew on December 20, 1957. Pan American World Airways inaugurated 707 service with a christening at National Airport on October 17, 1958, attended by President Eisenhower, followed by a transatlantic flight for VIPs (personal guests of founder Juan Trippe) from Baltimore's Friendship International Airport to Paris.[6] They began full 707 service with the type's first commercial flight on October 26, 1958. Subsequent derivatives included the shortened long-range 707-138 and the stretched 707-320, both of which entered service in 1959. A smaller short-range variant, the 720, was introduced in 1960. The 707-420, a version of the stretched 707 with Rolls-Royce Conway 508 turbofans, debuted in 1960, while Pratt & Whitney JT3D turbofans debuted on the 707-120B and 707-320B models in 1961 and 1962, respectively.

During its service career, the 707 has been used in a variety of roles, including domestic, transcontinental, and transatlantic operations. The 707 has also been used for cargo and military applications. A convertible passenger-freighter model, the 707-320C, entered service in 1963, and passenger 707s have been modified to freighter configurations. Military derivatives include the E-3 Sentry airborne reconnaissance aircraft and the C-137 Stratoliner VIP transports. During the 707's production run, Boeing produced and delivered a total of 1,011 aircraft, including the smaller 720 series. Over 800 military versions were also produced. As of August 2011, 10 examples of the 707 remain in airline service.

Development

Model 367-80 origins

Boeing, during and immediately after World War II, was known for its military aircraft. The company had produced innovative and important bombers, from the B-17 Flying Fortress and B-29 Superfortress, to the jet-powered B-47 Stratojet and B-52 Stratofortress. The company's civil aviation department lagged far behind Douglas and other competitors, the only noteworthy airliners being the Boeing 314 Clipper and 307 Stratoliner. During 1949–1950, Boeing embarked on serious studies for a new jet transport, realizing that any design must have the potential to fulfill both the military and civil markets. At the time, aerial refueling was increasingly becoming a standard operational technique, with over 800 KC-97 Stratotankers being on order. With the advent of the jet age, a new tanker was required to meets the USAF's fleet of jet-powered bombers; this was where Boeing's new design would potentially win military orders.

Boeing studied numerous wing and engine configurations for its new transport/tanker, some of which were based on the B-47 and C-97, before settling on 367-80. The "Dash 80" took less than two years from project launch in 1952 to rollout on May 14, 1954, then first flew on July 15, 1954. It was powered by the Pratt & Whitney JT3C turbojet engine, which was the civilian version of the J57 used on many military aircraft of the day, including the F-100 Super Sabre fighter and the B-52 bomber.The prototype was conceived as a proof of concept aircraft for both military and civilian use: The United States Air Force was the first customer for the design, using it as the basis for the KC-135 Stratotanker midair refueling platform.

It was far from certain that the passenger 707 would be profitable. At the time, Boeing was making nearly all of its money from military contracts: Its last passenger transport, the Boeing 377 Stratocruiser, had netted the company a $15 million loss before it was purchased by the Air Force as the KC-97 Stratotanker.[9] In a demonstration flight over Lake Washington outside of Seattle, on August 7, 1955, test pilot Tex Johnston performed a barrel roll in the 367-80 prototype.

The 132-inch (3,350 mm) wide fuselage of the Dash 80 was large enough to only fit four-abreast (two-plus-two) seating (in the manner of the Stratocruiser). Answering customers demands and under Douglas competition, Boeing soon realized that this would not provide a viable payload, so decided to widen the fuselage to 144 in (3,660 mm), the same as the KC-135 Stratotanker, which would allow five-abreast[disputed – discuss] seating—and the shared use of the KC-135's tooling.[10] However, Douglas Aircraft had launched its DC-8 with a fuselage width of 147 in (3,730 mm). The airlines liked the extra space and six-abreast seating, and so Boeing was obliged to increase the 707's width again to compete, this time to 148 in (3,760 mm).

Production and testing

The first flight of the first production 707-120 took place on December 20, 1957, and FAA certification followed on September 18, 1958.[12] A number of changes were incorporated into the production models from the prototype. A Krueger flap was installed along the leading edge between the inner and outer engines on early 707-120 and -320 models.[3][13]

Further developments

The initial standard model was the 707-120 with JT3C turbojet engines. Qantas ordered a shorter body version called the 707-138, which was a -120 that had six fuselage frames removed, three in front of the wings, and three aft. The frames in the 707 were each 20 inches (500 mm) apart, so this resulted in a net shortening of 10 ft (3 m) to 134 ft 6 in (41.0 m). Because the maximum takeoff weight remained the same 247,000 lb (112 t) as that of the -120, the 138 was able to fly the longer routes that Qantas needed.[13] Braniff International Airways ordered the higher-thrust version with Pratt & Whitney JT4A engines, the 707-220. The final major derivative was the 707-320, which featured an extended-span wing and JT4A engines, while the 707-420 was the same as the -320 but with Conway turbofan engines. British certification requirements relating to engine-out go-arounds also forced Boeing to increase the height of the tail fin on all 707 variants, as well as add a ventral fin, which was retrofitted on earlier -120 and -220 aircraft. These modifications also aided in the mitigation of dutch roll by providing more stability in yaw.

Though initially fitted with turbojet engines, the dominant engine for the Boeing 707 family was the Pratt & Whitney JT3D, a turbofan variant of the JT3C with lower fuel consumption as well as higher thrust. JT3D-engined 707s and 720s were denoted with a "B" suffix. While many 707-120Bs and 720Bs were conversions of existing JT3C-powered machines, 707-320Bs were available only as newly-built aircraft, as they had a stronger structure to support a maximum take-off weight increased by 19,000 lb (8,600 kg), along with minor modifications to the wing. The 707-320B series enabled non-stop westbound flights from Europe to the US west coast and from the US to Japan.

The final 707 variant was the 707-320C, (C for "Convertible"), which was fitted with a large fuselage door for cargo applications. This aircraft also had a significantly revised wing featuring three-section leading-edge flaps. This provided an additional improvement to takeoff and landing performance, and also allowed the ventral fin to be removed (although the taller fin was retained). 707-320Bs built after 1963 used the same wing as the -320C and were known as 707-320B Advanced aircraft.

Production of the passenger 707 ended in 1978. In total, 1,010 707s were built for civil use, though many of these found their way to military service. The purpose-built military variants remained in production until 1991.

Traces of the 707 are still found in the 737, which uses a modified version of the 707's fuselage, as well as the same external nose and cockpit configuration as the those of 707. These were also used on the previous 727, while the 757 also used the 707 fuselage cross-section. The Chinese government sponsored development of the Shanghai Y-10 during the 1970s, which was a near-carbon-copy of the 707; however, this did not enter production.

Design

Wings

The 707 wings are swept back at 35 degrees and, like all swept-wing aircraft, displayed an undesirable "Dutch roll" flying characteristic that manifested itself as an alternating yawing and rolling motion. Boeing already had considerable experience with this on the B-47 and B-52, and had developed the yaw damper system on the B-47 that would be applied to later swept wing configurations like the 707. However, many new 707 pilots had no experience with this phenomenon, as they were transitioning from straight-wing propeller-driven aircraft such as the Douglas DC-7 and Lockheed Constellation.

On one customer acceptance flight, where the yaw damper was turned off to familiarize the new pilots with flying techniques, a trainee pilot's actions violently exacerbated the Dutch roll motion and caused three of the four engines to be torn from the wings. The plane, a brand new 707-227, N7071, destined for Braniff, crash-landed on a river bed north of Seattle at Arlington, Washington, killing four of the eight occupants.[14]

In his autobiography, test pilot Tex Johnston described a Dutch roll incident he experienced as a passenger on an early commercial 707 flight. As the aircraft's movements did not cease and most of the passengers became ill, he suspected a misrigging of the directional autopilot (yaw damper). He went to the cockpit and found the crew unable to understand and resolve the situation. He introduced himself and relieved the ashen-faced captain who immediately left the cockpit feeling ill. Johnston disconnected the faulting autopilot and manually stabilized the plane "with two slight control movements".[15]

Engines

View of number 1 (top left) and 2 (center) Pratt & Whitney JT3D jet engines on the port side of a British Caledonian Boeing 707-320C. The number 1 engine mount (top) is different from the other three engines.

The 707s used engine-driven turbocompressors to supply high-pressure air for pressurization. The engines could not supply sufficient bleed air for this purpose without a serious loss of thrust. On many commercial 707s, the outer port (#1) engine mount is distinctly different from the other three, as this is the only engine not fitted with a turbocompressor, as seen in the adjoining image. With engines 2 through 4 being fitted with TCs, they provide the triple redundancy required of the aircraft's cabin pressurization and air-conditioning system.

The P&W JT3D-3B engines are readily identifiable by the large gray secondary air inlet doors in the nose cowl. These doors are fully open (sucked in at the rear) during takeoff to provide additional air. When the engines are throttled back to cruise, the doors are shut.

The 707 was the first commercial jet aircraft to be fitted with clamshell type thrust reversers on each of the four engines.

Upgraded engines

Pratt & Whitney, in a joint venture with Seven Q Seven (SQS) and Omega Air, has developed the JT8D-219[when?] as a re-engine powerplant for Boeing 707-based aircraft, calling their modified configuration a 707RE.[17] Northrop Grumman has selected the -219 to re-engine the United States Air Force's fleet of 19 E-8 Joint STARS aircraft, which will allow the J-STARS more time on station due to the engine's greater fuel efficiency. NATO also plans to re-engine their fleet of E-3 Sentry AWACS aircraft. The -219 is publicized as being half the cost of the competing 707 re-engine powerplant, the CFM International CFM56, and is 40 dB quieter than JT3D engines that are being replaced.[17]

Operational history

The first commercial orders for the 707 came on October 13, 1955,[18] when Pan Am committed to 20 707s and 25 Douglas DC-8s, a dramatic increase in passenger capacity over its existing fleet of propeller aircraft. The competition between the 707 and Douglas DC-8 was fierce. Several major airlines committed only to the DC-8, as Douglas Aircraft was a more established maker of passenger aircraft at the time. To stay competitive, Boeing made a late and costly decision to redesign and enlarge the 707's wing to help increase range and payload. The new version was numbered 707-320.

Pan Am was the first airline to operate the 707; the aircraft's first commercial flight was from New York to Paris on October 26, 1958 with a fuel stop in Gander, Newfoundland. In December, National Airlines operated the first U.S. domestic jet airline flights between New York/Idlewild and Miami, using 707s leased from Pan Am; American Airlines was the first domestic airline to fly its own jets, on January 25, 1959. TWA started domestic 707-131 flights in March and Continental Airlines started 707-124 flights in June; airlines that had ordered only the DC-8, such as United, Delta, and Eastern, were left without jets until September and lost market share on transcontinental flights. Qantas was the first non-US airline to use the 707s, starting in 1959.

The 707 quickly became the most popular jetliner of its time. Its popularity led to rapid developments in airport terminals, runways, airline catering, baggage handling, reservations systems, and other air transport infrastructure. The advent of the 707 also led to the upgrading of air traffic control systems to prevent interference with military jet operations.[19]

As the 1960s drew to a close, the exponential growth in air travel led to the 707's being a victim of its own success. The 707 was now too small to handle the increased passenger densities on the routes for which it was designed. Stretching the fuselage was not a viable option because the installation of larger, more powerful engines would in turn need a larger undercarriage, which was not feasible given the design's limited ground clearance. Boeing's answer to the problem was the first twin-aisle airliner—the Boeing 747. The 707's first-generation engine technology was also rapidly becoming obsolete in the areas of noise and fuel economy.

In 1982, during the Falklands War the Argentine Air Force extensively used civilian 707s for long-range maritime patrol, with some of them being intercepted and shepherded away by Royal Navy Sea Harriers,[20] it also led to the conversion of British Nimrods to carry Sidewinder air-to-air missiles after a casual encounter.

Trans World Airlines flew the last scheduled 707 flight for passengers by a US carrier on October 30, 1983,[21] although 707s remained in scheduled service by airlines from other nations for much longer. For example, Middle East Airlines (MEA) of Lebanon flew 707s and 720s in front-line passenger service until the end of the 1990s. Since LADE of Argentina took its 707-320B from regular service in 2007, Saha Airlines of Iran is the last airline to keep 707s in scheduled passenger service.

Operations of the 707 were threatened by the enactment of international noise regulations in 1985. Shannon Engineering of Seattle, Washington developed a hush kit with funding from Tracor, Inc, of Austin, Texas. By the late 1980s, 172 Boeing 707s had been equipped with the Quiet 707 package. Boeing acknowledged that more 707s were in service then than before the hush kit was available. Most remaining 707s are in freighter form, or as Business Jets.

Variants

Although certificated as Series 100s, 200s, 300s, etc., the different 707 variants are more commonly known as Series 120s, 220s, 320s, and so on, where the "20" part of the designation is Boeing's "customer number" for its development aircraft.

707-020

The original designation for what ultimately became the Boeing 720. Launch customer United Air Lines was a Douglas DC-8 customer and preferred not to be seen as buying the competing 707 hence the 720 designation. American Airlines always referred to its 720s as 707s.

707-120

The 707-120 was the first production 707 variant, with a longer, wider fuselage, and greater wingspan than the Dash-80. The cabin had a full set of rectangular windows and could seat up to 179 passengers. It was designed for transcontinental routes and often required a refuelling stop on the North Atlantic. It had four Pratt & Whitney JT3C-6 turbojets, civil versions of the military J57, initially producing 13,000 lb (57.8 kN) with water injection. Maximum takeoff weight was 247,000 lb and first flight was on December 20, 1957. Major orders were the launch order for 20 707-121 aircraft by Pan American and an American Airlines order for 30 707-123 aircraft. The first revenue flight was on October 26, 1958.[25] 56 were built, plus 7 short body -138s.

The 707-138 was a -120 with a fuselage ten feet shorter than the others, with 5 feet (3 frames) removed ahead and behind the wing, giving increased range. Maximum take off weight was the same 247,000 lb as the standard version. It was a variant for Qantas and had Boeing customer number 38 for Qantas. A total of 7 -138s were built, first carrying passengers in July 1959.

The 707-120B had Pratt & Whitney JT3D-1 turbofan engines, which were quieter, more powerful, and more fuel-efficient, producing 17,000 lbf (75.6 kN) each, with the later JT3D-3 version giving 18,000 lbf (80 kN). (This thrust did not require water injection, eliminating both the system and the 5000-6000 lb weight of the water itself.) The -120B had the wing modifications introduced on the 720 and a longer tailplane; a total of 72 were built, 31 for American and 41 for TWA, plus 6 short body -138Bs for Qantas. American had its 23 surviving -123s converted to 123Bs but TWA did not convert its 15 -131s. The only other conversions were Pan American's 5 surviving -121s and one surviving -139, the 3 aircraft delivered to the USAF as -153s and the 7 short body Qantas -138s. The first flight of the -120B was on 22 June 1960 and American carried the first passengers in March 1961. Maximum weight was 258,000 lb (117,025 kg) for both the long and short body versions.

707-220

The 707-220 was designed for hot and high operations with more powerful 15,800 lb (70.80 kN) Pratt & Whitney JT4A-3 turbojets. Five of these were produced, but only four were ultimately delivered with one being lost during a test flight. All were for Braniff International Airways and carried the model number 707-227; the first entered service in December 1959. This version was made obsolete by the arrival of the turbofan-powered 707-120B.

707-320

The 707-320 Intercontinental is a stretched version of the turbojet-powered 707-120, initially powered by JT4A-3 or JT4A-5 turbojets producing 15,800 lb (70.1 kN) each (most eventually got 17,500 lb (78.4 kN) JT4A-11s). The interior allowed for up to 189 passengers due to an 80-inch (2,000 mm) fuselage stretch ahead of the wing (from 138 ft 10 in (42.32 m) to 145 ft 6 in), with extensions to both the tail and horizontal stabilizer extending the aircraft's length further. while a longer wing carried more fuel, increasing range by 1,600 miles (2,600 km) and allowing the aircraft to operate as true transoceanic aircraft. The wing modifications included outboard and inboard inserts, as well as a kink in the trailing edge to add area inboard.[13] Takeoff weight was increased to 302,000 lb (137,000 kg) initially, and to 312,000 lb (142,000 kg) with the higher-rated JT4A's and centre section tanks. First flight was on January 11, 1958; 69 turbojet 707-320s were produced, the first passengers being carried (by Pan Am) in August 1959. No -320 Intercontinental models were re-engined with fan engines in civil use, but around year 2000 the Israeli Air Force re-engined two ex-Sabena -320 based military tankers.

707-420

The 707-420 was identical to the -320 but fitted with Rolls Royce Conway 508 turbofans (or by-pass turbojets as they were known at the time). First announced customer was Lufthansa. BOAC's controversial order was announced six months later but the British carrier got the first service-ready aircraft off the production line. The British Air Registration Board refused to give the aircraft a certificate of airworthiness in the form presented, citing insufficient lateral control, excessive rudder forces and the ability to over rotate on take off, stalling the wing on the ground (a fault of the de Havilland Comet 1). Boeing responded by adding 40 inches to the vertical tail, applying full instead of partial rudder boost and fitting an underfin to prevent over rotation. These modifications became standard on all 707 variants and were retrofitted to all previously built aircraft. Only 37 -420s were built, for BOAC, Lufthansa, Air-India, El Al and Varig; Lufthansa was the first to carry passengers, in March 1960.

707-320B

The 707-320B saw the application of the JT3D turbofan to the Intercontinental but with aerodynamic refinements. The wing was modified from the -320 by adding a second inboard kink, a dog-toothed leading edge, and curved low drag wingtips instead of the earlier blunt ones.[13] These new wingtips increased overall wingspan by three feet. Takeoff gross weight was increased to 328,000 lb (149,000 kg). The 175 707-320B aircraft were all new-build; no original -320 models were converted to fan engines in civilian use. First service was June 1962, with Pan Am.

The 707-320B Advanced is an improved version of the -320B, adding the three-section leading-edge flaps already seen on the -320C. These reduced takeoff and landing speeds and altered the lift distribution of the wing, allowing the ventral fin found on earlier 707s to be deleted. From 1965 -320Bs had the uprated -320C undercarriage allowing the same 335,000 lb (152,000 kg) MTOW. These were often identified as 707-320BA-H.

707-320C

The 707-320C has a convertible passenger–freight configuration, which became the most widely produced variant of the 707. The 707-320C added a strengthened floor and a new cargo door to the -320B model. The wing was fitted with three section leading edge flaps which allowed the deletion of the underfin. Three hundred thirty-five of these variants were built, including a small number with JT3D-7 engines (19000 lb takeoff thrust) and a takeoff gross weight of 335,000 lb (152,000 kg). Ironically, most -320Cs were delivered as passenger aircraft, airlines hoping that the cargo door would increase second hand values. The addition of two additional emergency exits, one on either side aft of the wing raised the maximum passenger capacity to a theoretical 219. Only a few aircraft were delivered as pure freighters. One of the final orders was by the Iranian Government for 14 707-3J9C aircraft capable of VIP transportation, communication, and in-flight refuelling tasks.

Other variants

The 707-700 was a test aircraft used to study the feasibility of using CFM International's CFM56 powerplants on a 707 airframe and possibly retrofitting them to existing aircraft. After a testing in 1979, N707QT, the last commercial 707 airframe, was refitted to 707-320C configuration and delivered to the Moroccan Air Force as a tanker aircraft. (This purchase was considered a "civilian" order and not a military one.) Boeing abandoned the program, since it felt it would be a threat to the Boeing 757 program. The information gathered in the test led to the eventual retrofitting program of CFM56 engines to the USAF C-135/KC-135R models, and some military versions of the 707 also used the CFM56. It is ironic that the Douglas DC-8 "Super 70" series by Cammacorp did develop commercially, extending the life of DC-8 airframes in a stricter noise regulatory environment, so there are today more DC-8s in commercial service than there are 707s.

Military

The militaries of the United States and other countries have used the civilian 707 aircraft in a variety of roles, and under different designations. (Note the 707 and U.S. Air Force's KC-135 were developed in parallel from the Boeing 367-80 prototype.)

The Boeing E-3 Sentry is a U.S. military airborne warning and control system (AWACS) aircraft based on the Boeing 707 that provides all-weather surveillance, command, control and communications.

The VC-137C variant of the Stratoliner was a special-purpose design meant to serve as Air Force One, the secure transport for the President of The United States of America. These models were in operational use from 1962 to 1990. The two aircraft remain on display: SAM 26000 is at the National Museum of the United States Air Force near Dayton, Ohio and SAM 27000 is at the Ronald Reagan Presidential Library in Simi Valley, California.

The Canadian Forces also operated Boeing 707 with designation CC-137 Husky (707-347C) from 1972 to 1997.