|Trans Polar Boeing 720 arriving at Stockholm-Arlanda Airport in June 1970|
|Role||Narrow-body jet airliner|
|National origin||United States|
|Manufacturer||Boeing Airplane Company|
|First flight||November 23, 1959|
|Introduction||July 5, 1960 with United Airlines|
|Retired||September 29, 2010|
|Primary users||United Airlines
|Developed from||Boeing 707|
The Boeing 720 was a four-engine narrow-body short- to medium-range passenger jet airliner. Developed by Boeing in the late 1950s from the Boeing 707, the 720 has a shorter fuselage and less range. The 720 first flew in November 1959 and the model entered service with launch customer United Airlines in July 1960.
Two primary versions of the aircraft were built. The original 720 with Pratt & Whitney JT3C turbojet engines entered service in 1960, while the improved 720B with Pratt & Whitney JT3D turbofans entered service in 1961. Some 720s were later converted to 720B specification.
Although only 154 were built, the Boeing 720/720B was still profitable due to the low research and development costs of it being a slightly modified version of the 707-120. It was later replaced by the Boeing 727.
Shorter range 707
Boeing announced its plans to develop a new version of the 707 in July 1957. It was developed from the 707-120 to provide for airline operation for short to medium range flights from shorter runways. The model was originally designated 707-020 before being changed to 720 at the input of United Airlines. Compared to the 707-120, it has four fewer frames in front of the wing and one fewer aft: a total length reduction of 8 feet 4 inches (2.54 m).
The new model was designed to a lower maximum takeoff weight with a modified wing and a lightened airframe. The wing modifications included Krueger flaps outboard of the outboard engines, lowering takeoff and landing speeds—thus shortening runway length requirements—and a thickened inboard leading edge section, with a slightly greater sweep. This modification increased the top speed over the -120. It had four Pratt & Whitney JT3C-7 turbojet engines producing 12,500 lbf (55.6 kN) each.
At one point in the development phase, it was known as the 717-020, although this was the Boeing model designation of the KC-135 and remained unused for a commercial airliner until it was applied to the MD-95 following Boeing's merger with McDonnell Douglas in 1997.
Because the aircraft systems were similar to the Boeing 707 no prototype Boeing 720 was built; any different systems were tested on the Boeing 367-80. The first 720 took its maiden flight on November 23, 1959. The Type Certificate for the 720 was issued on June 30, 1960. It was first put into service by United Airlines on July 5, 1960. 65 of the original version were built.
The 720B was the version of the 720 with JT3D turbofan engines, producing 17,000 lbf (75.6 kN) each. The JT3D engines had lower fuel consumption and higher thrust. The maximum takeoff weight for the 720B was increased to 234,000 lb (106,000 kg). The 720B first took to the skies on October 6, 1960 and received certification and entered service with American Airlines in March 1961. 89 720Bs were built, in addition to conversions of American's ten existing 720s.
As a modification of an existing model the 720 had minimal research and development costs, which allowed it to be successful despite few sales. The company built 154 Boeing 720s and 720Bs from 1959 to 1967. The 720's wing modification was later added on the -120B and on -120s retrofitted to the B standard.
The Boeing 720 is a four-engined low-wing cantilever monoplane. Although it was similar to the Boeing 707, compared with the 707-120 it was 9 ft (2.73 m) shorter in length, and had a lighter structure through use of lighter forged metal parts and thinner fuselage skins and structures.
The rearmost of the 707's over-wing emergency exits was deleted on each side which reduced passenger capacity, while two over-wing exits were an option for higher-density configurations.
The 720 uses an improved wing based on the 707 wing. The wingspan remained the same as the 707-120. For the 720, the wing was changed between the fuselage and inner engines by adding a wing root glove. This glove reduced the drag of the wing by decambering the root, which reduced the "middle effect", thereby increasing the effective local wing sweep. It is reported that the wing root glove increased the drag divergence Mach number of the wing by Mach 0.02.
Though initially fitted with turbojet engines, the dominant engine for the Boeing 720 was the Pratt & Whitney JT3D, a turbofan variant of the JT3C with lower fuel consumption and higher thrust. JT3D-engined 720s had a "B" suffix; some of American's 720Bs were conversions of JT3C-powered 720s.
Like the 707, the 720/720B 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. The small air inlets and associated humps are visible just above the main engine inlets on the two inner engine pods of all 720s and 720Bs; the lack of the turbocompressor inlet on the outer starboard pod (no.4 engine) helps spotters distinguish 720/720Bs from most 707s, which had three turbocompressors.
The Boeing 720 lacked an APU, and was reliant instead on ground power and pneumatic air to power the aircraft's systems, provide air conditioning, and start the engines while on the ground. The normal practice for Boeing 720 aircraft was to start the number 3 (inner starboard) engine first, disconnect ground power and air. After start of the first engine the use of bleed air from that engine could be used to provide necessary air pressure to start the other engines one by one. However on ground, with ground starting crew already at hand, all four engines were usually started with ground crew help as this was more reliable and faster.
The first aircraft was a production aircraft for United Airlines which flew on November 23, 1959. The Type Certificate for the 720 was issued on June 30, 1960. The first service of the 720 was by United Airlines on July 5, 1960 on the Los Angeles-Denver-Chicago route. American Airlines followed by putting the 720 in commercial operation on July 31 that same year. The 720 was supplanted by the Boeing 727 in the mid-1960s in its medium-range, high-performance market.
After disposal of examples of the type by the major airlines, many were acquired by second rank operators in South America and elsewhere.
In 1984 a Boeing 720 flown by remote control was intentionally crashed at Edwards AFB as a part of the FAA and NASA Controlled Impact Demonstration program. The test provided peak accelerations during a crash. The performance of fire-retardant fuel was also tested.
The first 720 (N7201U) was later renamed "The Starship" and become a private charter jet used mainly by touring rock bands. Its main user was Led Zeppelin in the 1970s. The seating capacity was reduced and a bar with a built-in electric organ were added, along with beds, a shower, a lounge area, a TV and video cassette player.
Honeywell operated the last Boeing 720 in operation in the United States, flying out of Sky Harbor airport in Phoenix. The aircraft had been modified with an extra engine nacelle mounted on the right side of the fuselage to allow testing of a turbine engine at altitude, operating on special certification allowing it to be used for experimental use. This 720B was scrapped on June 21 and 22, 2008. Honeywell replaced their aircraft with a Boeing 757.
Pratt & Whitney Canada operated the last flying 720 until 2010. Its final operational flight occurred on September 29, 2010. Pratt & Whitney Canada replaced the testbed with a Boeing 747SP. In May 2012, the former PWC 720 was flown to CFB Trenton, ON to be put on display at the National Air Force Museum of Canada.
- First production variant with four Pratt & Whitney JT3C turbojet engines.
- Several high-density seat configurations delivered to Eastern Airlines included 4 over-wing escape hatches and brake cooling fans to effect quick turns on short-haul sectors.
- Improved variant with four Pratt & Whitney JT3D turbofan engines. American Airlines converted its 720s to 720B standard.
The following operators flew Boeing 720/720Bs:
- Kenya Airways 720B
- Middle East Airlines 720B
- Air Malta 5 x 720B used from 1974 to 1988
- American Airlines 10 x 720 delivered in 1960 and 15 x 720Bs delivered in 1961, the ten 720s were converted to turbofan powered B models in 1961
- Braniff International Airways 5 x 720 delivered 1961–1963, an additional aircraft was sold to the Federal Aviation Agency before delivery
- Continental Airlines 8 x 720B delivered 1962–1966
- Eastern Airlines 15 x 720 delivered 1961–1962
- Federal Aviation Agency one 720 delivered in 1960 or 1961
- Northwest Airlines 13 x 720B delivered 1961–1964
- Pacific Northern Airlines 2 x 720 delivered in 1962
- Pan American World Airways 9 x 720B delivered in 1961
- United Airlines 29 x 720 delivered 1960–1962 (several also leased by United to Capital Airlines in 1960)
- Western Airlines 27 x 720Bs delivered 1961–1967
Accidents and incidents
The Boeing 720 has had 23 hull-loss accidents during its career; it was also involved in a number of incidents including nine hijack incidents and one aircraft destroyed by a bomb in mid-air in 1976. Only 12 of the hull-loss accidents included fatalities which totaled 175 deaths in addition to the 81 deaths on the aircraft destroyed in mid-air by a bomb.
The worst accidents were:
- On February 12, 1963, Northwest Orient Airlines Flight 705, a Boeing 720-051B (reg. N724US), suffered an in-flight break-up over the Florida Everglades approximately 12 minutes after leaving Miami, bound for Chicago. All 35 passengers and eight crew died. The cause of the crash was determined to be an unrecoverable loss of control due to severe turbulence.
- On May 20, 1965, Pakistan International Airlines Flight PK 705, 720-040B (reg AP-AMH), crashed short of the runway at Cairo International Airport, killing 121 of the 127 people on board.
- On January 1, 1976, Middle East Airlines Flight 438, a Boeing 720-023B (reg. OD-AFT), was destroyed en route from Beirut to Dubai by a bomb in the forward cargo hold. All 66 passengers and 15 crew were killed.
Aircraft on display
- 720-051B 18351 a former Republic of China Air Force VIP aircraft on display at Kangshan, Taiwan.
- 720-030B HK-749 on display at Museo de los Ninos (Children's Museum of Bogotá), Bogotá, Colombia in Avianca Colombia livery. It was first jet airplane to a Colombian company, Avianca.
|Cockpit crew||Four (Pilot, Co-Pilot, Flight Engineer, Navigator)|
|Passengers||149||110 (2 class)
189 (1 class)
|147 (2 class)
189 (1 class)
|Length||136 ft 2 in (41.25 m)||145 ft 1 in (44.07 m)||152 ft 11 in (46.61 m)|
|Wingspan||130 ft 10 in (39.90 m)||145 ft 9 in (44.42 m)|
|Tail height||41 ft 7 in (12.65 m)||42 ft 5 in (12.93 m)|
|Maximum Takeoff Weight (MTOW)||222,000 lb (100,800 kg)||257,000 lb (116,570 kg)||333,600 lb (151,320 kg)|
|Empty weight||103,145 lb (46,785 kg)||122,533 lb (55,580 kg)||146,400 lb (66,406 kg)|
|Runway needed at MTOW||8,300 ft (2,515 m)||11,000 ft (3,330 m)||10,840 ft (3,280 m)|
|Fuel Capacity||16,060 US gal (60,900 L)||17,330 US gal (65,590 L)||23,820 US gal (90,160 L)|
|Landing run||5,750 ft (1,740 m)||6,200 ft (1,875 m)||5,950 ft (1,813 m)|
|Operating range (max. payload)||3,680 nmi (6,820 km)||3,735 nmi (6,920 km)|
|Range at MTOW (max. fuel)||3800 nmi (7,040 km)||4,700 nmi (8,704 km)||5,750 nmi (10,650 km)|
|Cruising speed||540 kn / 621 mph (1000 km/h)||525 kn/604 mph (972 km/h)|
|Fuselage width||12 ft 4 in (3.76 m)|
|Powerplants (4 x)||Pratt & Whitney JT3C-7:
12,000 lbf (53.3 kN)
|Pratt & Whitney JT3D-1:
17,000 lbf (75.6 kN)
18,000 lbf (80 kN)
19,000 lbf (84.4 kN)
- Related development
- Aircraft of comparable role, configuration and era
- Related lists
- Niles, Russ. "Last Boeing 720 Retired." avweb.com, October 5, 2010. Retrieved: October 26, 2010.
- Angelucci, Enzo; Paolo Matricardi and Adriano Zannino. The Illustrated Encyclopedia of Civil Aircraft: From Leonardo da Vinci to the Present, p. 346. Edison, New Jersey US: Chartwell Books, 2001. ISBN 0-7858-1389-6.
- "Boeing 720". Boeing Commercial Airplanes. Retrieved July 7, 2011.
- Frawley, Gerald. "Boeing 720". The International Directory of Civil Aircraft, 2003/2004. Fishwick, Act: Aerospace Publications, 2003. ISBN 1-875671-58-7.
- Donald, David, ed. The Complete Encyclopedia of World Aircraft. New York: Barnes & Noble Books, 1997. ISBN 0-7607-0592-5.
- Lombardi, Michael. "The first KC-135 rolled out 50 years ago this month." Historical Perspective, Start of a Proud Mission: Boeing Frontiers, July 2006. Retrieved: April 17, 2010.
- Pither 1998, p. 29.
- Boeing 720. Boeing
- "Boeing 720". Airliners.net. Retrieved January 10, 2012.
- Pither 1998, p. 30
- Proctor 2010, p. 120.
- "Boeing 707/720 Short History." Boeing. Retrieved: December 27, 2009.
- "Boeing 707." airlinercafe.com. Retrieved: December 27, 2009.
- Proctor 2010, p. 119.
- Proctor 2010, p. 118.
- "The Boeing 720". Flight, August 19, 1960.
- The Ultimate Boeing 707 Guide Retrieved September 5, 2011.
- Cook, William H. The Road to the 707: The Inside Story of Designing the 707. Bellevue, Washington: TYC Publishing, 1991. ISBN 978-0-9629605-0-5.
- "Flight test experience and controlled impact of a remotely piloted jet transport aircraft, NASA-TM-4084." NASA, November 1, 1988. Retrieved: December 27, 2009.
- Film "The Song Remains The Same"
- "Resident Boeing 720B." visitingphx.com. Retrieved: December 27, 2009.
- Niles, Russ. "Last Boeing 720 Retired." avweb.com, October 5, 2010. Retrieved: October 26, 2010.
- nurun.com (2012-05-10). "Historic landing a success". Trentonian.ca. Trenton Trentonian. Retrieved 2013-03-27.
- Pither 1998, p. 137.
- Pither 1998, p. 157.
- Pither 1998, p. 176.
- Pither 1998, pp. 116–117.
- Pither 1998, p. 156.
- Pither 1998, pp. 186–187.
- "History of Air Rhodesia." Viscounts in Africa: The Air Rhodesia Story. Retrieved: 7 February 2014.
- Pither 1998, p. 133.
- Pither 1998, p. 142.
- Pither 1998, p. 151.
- Pither 1998, pp. 154–155.
- Federal Aviation Administration (September 1987). "Full-Scale Transport Controlled Impact Demonstration Program" (PDF). Atlantic City International Airport, New Jersey: FAA Technical Center. p. 5. DOT/FAA/CT-87/10, NASA-TM-89642. Retrieved September 2, 2014.
This was the first time that a four-engine jet aircraft (Boeing 720) had been flown successfully by remote control. It was also the first time that an aircraft was flown solely and successfully on antimisting kerosene fuel (AMK).
- Pither 1998, p. 158.
- Pither 1998, pp. 183–184.
- Pan American World Airways#Fleet
- Pither 1998, pp. 212–213.
- Pither 1998, p. 215-216.
- "Boeing 720". Aviation Safety Network. Retrieved 19 October 2013.
- "Northwest Airlines flight 705." Aviation-Safety.net. Retrieved: December 27, 2009.
- "ASN Aircraft accident Boeing 720-040B AP-AMH Cairo International Airport (CAI)". Aviation-safety.net. 1965-05-20. Retrieved 2013-03-27.
- Bladd, Joanne. "MEA flight 438." Aviation-Safety.net. Retrieved: December 27, 2009.
- Pither 1998, p. 311.
- Pither 1998, p. 308.
- Franco, Javier. "Uniendo el maletín retro de Avianca con sus Boeing 720 y 727". Retrieved 26 December 2014.
- FAA Type Certificate Data Sheet http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8b6ebaa7513ba29a852567240060420c/$FILE/4a21.PDF
- "Boeing 720." Boeing, May 2011. Retrieved: December 27, 2009.
- "707 Airplane Characteristics: Airport Planning." Boeing, May 2011. Retrieved: September 21, 2012.
- "Boeing 707 Family." Boeing. Retrieved: December 27, 2009.
- Francillon, René. Boeing 707: Pioneer Jetliner. Shrewsbury, Shropshire, UK: Motor Books International, 1999. ISBN 0-7603-0675-3
- Pither, Tony (1998). The Boeing 707 720 and C-135. England: Air-Britain (Historians) Ltd. ISBN 0-85130-236-X.
- Proctor, Jon (2001). Boeing 720. Miami, FL: World Transport Press. ISBN 1-892437-03-1.
- Proctor, Jon; Mike Machat; Craig Kodera (2010). From Props to Jets: Commercial Aviation's Transition to the Jet Age 1952–1962. North Branch, MN: Specialty Press. ISBN 978-1-58007-146-8.
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