Editing Boeing 707 (section)

==Variants==
{{more citations needed section|date=December 2016}}
Although certified 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 [[List of Boeing customer codes|Boeing's "customer number"]] for its development aircraft.

===707-020===
[[File:Cyprus Airways Boeing 720B G-BCBB LHR 1978-8-24.png|thumb|The 707-020 (720) is 9 ft (2.7 m) shorter than the 707-120.]]
{{main|Boeing 720}}

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Announced in July 1957 as a derivative for shorter flights from shorter runways, the 707-020 first flew on November 23, 1959. Its type certificate was issued on June 30, 1960, and it entered service with United Airlines on July 5, 1960. As a derivative, the 720 had low development costs, allowing profitability despite few sales.

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Compared to the 707-120, it has a length reduced by 9 feet (2.7 m), a modified wing and a lightened airframe for a lower [[maximum takeoff weight]]. Powered by four Pratt & Whitney JT3C turbojets, the initial 720 could cover a {{cvt|2,800|nmi}} range with 131 passengers in two classes.
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Powered by JT3D turbofans, the 720B first flew on October 6, 1960, and entered service in March 1961. It could seat 156 passengers in one class over a {{cvt|3,200|nmi}} range. A total of 154 Boeing 720s and 720Bs were built until 1967. Some 720s were later converted to the 720B specification. The 720 was succeeded by the Boeing 727 trijet.

[[File:Boeing 707-120 without “eyebrow windows”.jpg|alt=Boeing 707-120 without "eyebrow windows"|thumb|Boeing 707-120, the aircraft's first production variant]]

===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 189 passengers.<ref>PA, AA, TW and CO 707-120s started with 109–112 "revenue" seats and maybe a few lounge seats.{{citation needed|date=February 2012}}</ref> It was designed for transcontinental routes, and often required a refueling stop when flying across the North Atlantic. It had four Pratt & Whitney JT3C-6 turbojets, civilian versions of the military J57, initially producing {{cvt|13,000|lbf|kN|1}} with [[Water injection (engines)|water injection]]. Maximum takeoff weight was {{cvt|247,000|lb}} and first flight was on December 20, 1957. Major orders were the launch order for 20 707-121 aircraft by Pan Am and an American Airlines order for 30 707-123 aircraft. The first revenue flight was on October 26, 1958;<ref name="Pither22">{{harvnb|Pither|1998|p=22}}</ref> 56 were built, plus seven short-bodied -138s; the last -120 was delivered to Western in May 1960.

===707-138===
The 707-138 featured a -120 fuselage, from which {{cvt|5|ft}} (three frames) were removed both ahead of and behind the wing, increasing range. The maximum takeoff weight remained the same as the standard version, at {{cvt|247,000|lb}}. The variant was produced for Qantas and included their customer number, 38, in its designation. To allow for full-load takeoffs at the midflight refueling stop in Fiji, the wing's leading-edge slats were modified for increased lift, and the allowable temperature range for use of full takeoff power was increased by 10&nbsp;°F (5.5&nbsp;°C).{{citation needed|date=January 2024}} Seven -138s were delivered to Qantas between June and September 1959, and they first carried passengers in July of that year.

===707-120B===
The 707-120B had Pratt & Whitney JT3D-1 turbofan engines, which were quieter, more powerful, and more fuel-efficient, rated at {{cvt|17000|lbf|kN|sigfig=3}}, with the later JT3D-3 version giving {{cvt|18000|lbf|kN}}. (This thrust did not require water injection, eliminating both the system and 5000–6000&nbsp;lb of water.) 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 six short-bodied -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 Am's five surviving -121s and one surviving -139, the three aircraft delivered to the USAF as -153s and the seven short-bodied Qantas -138s (making 13 total 707s delivered to Qantas between 1959 and 1964).{{citation needed|date=January 2024}} The first flight of the -120B was on June 22, 1960, and American carried the first passengers in March 1961; the last delivery was to American in April 1969. Maximum weight was {{cvt|258,000|lb|kg}} for both the long- and short-bodied versions.

===707-220===
The 707-220 was designed for [[hot and high]] operations with more powerful {{cvt|15,800|lbf|kN|1}} 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 Intercontinental===
[[File:Air France Boeing 707-328 (cropped).jpg|thumb|The stretched -320, powered by [[JT4A]] turbojets]]

The 707-320 Intercontinental is a stretched version of the turbojet-powered 707-120, initially powered by JT4A-3 or JT4A-5 turbojets producing {{cvt|15,800|lbf|kN|1}} each (most eventually got {{cvt|17,500|lbf|kN|1}} JT4A-11s). The interior allowed up to 189 passengers, the same as the -120 and -220 series, but improved two-class capacity due to an 80-in fuselage stretch ahead of the wing (from {{cvt|138|ft|10|in}} to {{cvt|145|ft|6|in}} ), with extensions to the fin and horizontal stabilizer extending the aircraft's length further.<ref name=707acaps/> The longer wing carried more fuel, increasing range by {{convert|1600|mi|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.<ref name="airlinercafe.com"/> Takeoff weight was increased to {{cvt|302000|lb|sigfig=3}} initially and to {{cvt|312000|lb}} with the higher-rated JT4As and center section tanks. Its first flight was on January 11, 1958; 69 turbojet 707-320s were delivered through January 1963, the first passengers being carried (by Pan Am) in August 1959.

===707-420===
[[File:BEA Airtours 707-400 (cropped).jpg|thumb|A [[British Airtours|BEA Airtours]] -420, powered by [[Rolls-Royce Conway]] low-bypass turbofans]]

The 707-420 was identical to the -320, but fitted with Rolls-Royce Conway 508 (RCo.12) turbofans (or by-pass turbojets as Rolls-Royce called them) of {{cvt|18,000|lbf|kN}} thrust each.<ref>{{cite web |url=http://www.flightglobal.com/pdfarchive/view/1961/1961%20-%201700.html |title= Commercial aircraft - sq ft - ias - 1961 - 1700 - Flight Archive |work=FlightGlobal |access-date=April 1, 2015}}</ref> The 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, citing insufficient yaw control, excessive rudder forces, and the ability to over-rotate on takeoff, stalling the wing on the ground (a fault of the de Havilland Comet 1). Boeing responded by adding {{convert|40|in|cm|abbr=on}} to the vertical stabilizer, applying full instead of partial rudder boost, and fitting an underfin to prevent over-rotation. These modifications except to the fin under the tail became standard on all 707 variants and were retrofitted to all earlier 707s. The 37 -420s were delivered to BOAC, Lufthansa, [[Air-India]], [[El Al]], and [[Varig]] through November 1963; Lufthansa was the first to carry passengers, in March 1960.

===707-320B===
[[File:CAAC Boeing 707.jpg|thumb|The -320B, powered by [[JT3D]] turbofans]]

The 707-320B had 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.<ref name="airlinercafe.com"/> These wingtips increased overall wingspan by 3.0&nbsp;ft (0.9 m). Takeoff gross weight was increased to {{cvt|328000|lb|kg|sigfig=3}}. 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 removed. From 1965, -320Bs had the uprated -320C undercarriage allowing the same {{cvt|335000|lb|kg|sigfig=3}} MTOW. These were often identified as 707-320BA-H.

===707-320C===
[[File:Ecuatoriana Boeing 707-321C Hoppe.jpg|thumb|The 707-320C, a [[combi aircraft|convertible]] passenger–freight configuration]]

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 removal of the underfin. A total of 335 of this variant were built, including some with JT3D-7 engines ({{cvt|19,000|lbf|kN}} takeoff thrust) and a takeoff weight of {{cvt|335000|lb}}. Most -320Cs were delivered as passenger aircraft with airlines hoping the cargo door would increase second-hand values. The addition of two new emergency exits, one on each side aft of the wing, raised the maximum passenger limit to 219.{{Citation needed|date= January 2019}} 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 refueling tasks.<ref>{{citation |url= https://www.alef.ir/news/3971024133.html |title=جزئیات پرواز ۱۴ فروند بوئینگ ۷۰۷ در ایران/توقف تولید ۷۰۷ از سال ۱۹۷۹ |work=جامعه خبری تحلیلی الف |language=fa |archive-url=https://web.archive.org/web/20200115020535/https://www.alef.ir/news/3971024133.html |date=December 24, 2016 |archive-date=January 15, 2020 |access-date=November 30, 2021 |url-status=live}}</ref>

===707-700===
The 707-700 was a test aircraft used to study the feasibility of using CFM International CFM56 engines on a 707 airframe and possibly retrofitting existing aircraft with the engine. After testing in 1979, ''N707QT'', the last commercial 707 airframe, was restored to 707-320C configuration and delivered to the Moroccan Air Force as a tanker aircraft via a "civilian" order. Boeing abandoned the retrofit program, since they felt it would be a threat to the 757 and 767 programs.<ref name="Bowers445">{{harvnb|Bowers|1989|pp=445, 446}}</ref><ref>The last 707 ''[[Australian Aviation]]'' issue June 15, 1982, page 44</ref> The information gathered from testing led to the eventual retrofitting of CFM56 engines to the USAF C-135/KC-135R models, and some military versions of the 707 also used the CFM56. The Douglas DC-8 "Super 70" series with CFM56 engines was developed and extended the DC-8's life in a stricter noise regulatory environment. As a result, significantly more DC-8s remained in service into the 21st century than 707s.{{citation needed|reason=Paragraph needs citing|date=February 2015}}

===Undeveloped variants===
The 707-620 was a proposed domestic range-stretched variant of the 707-320B. The 707-620 was to carry around 200 passengers while retaining several aspects of the 707-320B. It would have been delivered around 1968 and would have also been Boeing's answer to the stretched [[Douglas DC-8#Super 60 Series|Douglas DC-8 Series 60]]. Had the 707-620 been built, it would have cost around US$8,000,000.<ref name="FI1">{{cite press release |url=http://www.flightglobal.com/pdfarchive/view/1965/1965%20-%200802.html| title=T0WARD8 200-SEAT BOEINGS| publisher=[[Flight International]]|date=March 25, 1965 |access-date=December 12, 2012}}</ref> However, engineers discovered that a longer fuselage and wing meant a painstaking redesign of the wing and landing-gear structures. Rather than spend money on upgrading the 707, engineer [[Joe Sutter]] stated the company "decided spending money on the 707 wasn't worth it". The project was cancelled in 1966 in favor of the newer Boeing 747.<ref name="MH">{{cite book |title=Boeing Widebodies |publisher=Zenith Press |author=Haenggi, Michael |year=2003 |location=Saint Paul, Minnesota |pages=[https://archive.org/details/boeingwidebodies00mich/page/15 15 and 17] |isbn=978-0-7603-0842-4 |url=https://archive.org/details/boeingwidebodies00mich/page/15}}</ref>

The 707-820 was a proposed intercontinental stretched variant of the 707-320B. This {{convert|412,000|lb|kg|adj=mid|MTOW}} variant was to be powered by four {{convert|22,500|lbf|kN|adj=mid|thrust}} Pratt & Whitney JT3D-15 turbofan engines, and it would have had a nearly {{convert|10|ft|m|adj=on}} extension in wingspan, to {{convert|155.5|ft}}. Two variations were proposed, the 707-820(505) model and the 707-820(506) model. The 505 model would have had a fuselage {{convert|45|ft|m}} longer than the 707-320B, for a total length of {{convert|198.6|ft|m}}. This model would have carried 209 passengers in mixed-class configuration and 260 passengers in all-economy configuration. The 506 model would have had a fuselage {{convert|55|ft|m}} longer than the 707-320B, to {{convert|208.6|ft|m}} in length. This second model would have carried 225 passengers in mixed-class configuration and 279 passengers in all-economy configuration. Like the 707-620, the 707-820 was also set to compete with the stretched DC-8-60 Super Series models. The design was being pitched to American, TWA, BOAC, and Pan Am at the time of its proposal in early 1965.<ref name="FI19650603">{{cite magazine |url=http://www.flightglobal.com/pdfarchive/view/1965/1965%20-%201564.html |title=Boeing 707-820: First details of the longer, faster, heavier and more powerful new 279-seat Boeing |publisher=[[Flight International]] |pages=860+ |date=June 3, 1965 |access-date=December 12, 2012 |url-status=dead |archive-date=April 20, 2016 |archive-url=https://web.archive.org/web/20160420233731/http://www.flightglobal.com/pdfarchive/view/1965/1965%20-%201564.html}}</ref> The 707-820 would have cost US$10,000,000.<ref name="FI1" /> Like the 707-620, the 707-820 would have required a massive structural redesign to the wing and gear structures. The 707-820 was also cancelled in 1966 in favor of the 747.<ref name="MH"/>

===Military versions===
[[File:RAAF Boeing 707-338C CBR Gilbert-2.jpg|thumb|[[RAAF]] 707-320C]]
{{Main|C-137 Stratoliner|E-3 Sentry|E-6 Mercury|E-8 Joint STARS|Air Force One}}

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

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

The [[Northrop Grumman E-8 Joint STARS]] is an aircraft modified from the Boeing 707-300 series commercial airliner. The E-8 carries specialized radar, communications, operations and control subsystems. The most prominent external feature is the 40&nbsp;ft (12 m) canoe-shaped radome under the forward fuselage that houses the 24&nbsp;ft (7.3 m) APY-7 active electronically scanned array side looking airborne radar antenna.

The VC-137 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]]. These models were in operational use from 1962 to 1990. The first presidential jet aircraft, a VC-137B designated SAM 970, is on display at the [[Museum of Flight]] in Seattle. Two VC-137C aircraft are on display with [[VC-137C SAM 26000|SAM 26000]] at the [[National Museum of the United States Air Force]] near [[Dayton, Ohio]] and [[VC-137C SAM 27000|SAM 27000]] at the [[Ronald Reagan Presidential Library]] in [[Simi Valley, California]].
[[File:IIAF Boeing 707 refuels IIAF Boeing 747.jpg|thumb|An [[Air force history of Iran|Imperial Iranian Air Force]] KC707 refuels an IIAF Boeing 747]]
The [[Canadian Forces]] also operated the Boeing 707 with the designation [[Boeing CC-137|CC-137 Husky]] (707-347C) from 1971 to 1997.

Boeing 717 was the company designation for the [[Boeing C-135 Stratolifter|C-135 Stratolifter]] and [[Boeing KC-135 Stratotanker|KC-135 Stratotanker]] derivatives of the 367-80. (The 717 designation was later reused in renaming the McDonnell Douglas MD-95 to [[Boeing 717]] after the company merged with Boeing.)<ref>[http://www.boeing.com/news/frontiers/archive/2006/july/i_history.pdf "Historical Perspective, Start of a PROUD MISSION"] {{Webarchive|url=https://web.archive.org/web/20140612010633/http://www.boeing.com/news/frontiers/archive/2006/july/i_history.pdf |date=June 12, 2014}}. ''Boeing Frontiers'', July 2006.</ref>