| Boeing 720 | |
|---|---|
 The 720 is similar to theBoeing 707 with a slightly shorter fuselage. Here, a 720 inCyprus Airways (1947–2015) livery is landing at London Heathrow Airport | |
| General information | |
| Role | Narrow-bodyjet airliner |
| National origin | United States |
| Manufacturer | Boeing Commercial Airplanes |
| Status | Retired |
| Primary users | United Airlines |
| Number built | 154[1] |
| History | |
| Manufactured | 1959–1967[2][3] |
| Introduction date | July 5, 1960, with United Airlines |
| First flight | November 23, 1959 |
| Retired | September 29, 2010[4] |
| Developed from | Boeing 707 |
TheBoeing 720 is a retired Americannarrow-body airliner produced byBoeing Commercial Airplanes. Announced in July 1957 as a707 derivative for shorter flights from shorter runways, the 720 first flew on November 23, 1959. Its type certificate was issued on June 30, 1960, and it entered service withUnited Airlines on July 5, 1960. A total of 154 Boeing 720s and 720Bs were built; production ended in 1967. As a derivative, the 720 had low development costs, allowing profitability despite relatively few sales.
Compared to the 707-120, it has a length reduced by 8.33 feet (2.54 m), a modified wing and a lightened airframe for a lowermaximum takeoff weight. Originally designed to be powered by fourPratt & Whitney JT3C turbojets, the initial 720 could cover a 2,800-nautical-mile [nmi] (5,200 km; 3,200 mi) range with 131 passengers in two classes. The reconfigured 720B, powered byJT3D turbofans, first flew on October 6, 1960, and entered service in March 1961. It could seat 156 passengers in one class over a 3,200-nautical-mile [nmi] (5,900 km; 3,700 mi) range. Some 720s were later converted to the 720B specification. It was succeeded by theBoeing 727 trijet.
Boeing announced its plans to develop a new version of the 707 in July 1957.[1] It was developed from the 707-120 to provide for short- to medium-range flights from shorter runways. The model was originally designated 707-020 before being changed to 720 at the input ofUnited Airlines.[5] Compared to the707-120, 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).[6]
The new model was designed to a lower maximum takeoff weight with a modified wing and a lightened airframe. The wing modifications includedKrueger flaps outboard of the outboard engines, lowering take-off 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 the707-120.[6] It had fourPratt & Whitney JT3C-7 turbojet engines producing 12,500 lbf (55.6 kN) each.[7]
At one point in the development phase, it was known as the 707-020, then 717-020,[5] although this was the Boeing model designation of the KC-135 and remained unused for a commercial airliner until it was applied to theMD-95, followingBoeing's merger withMcDonnell Douglas in 1997.[8]
Because the aircraft systems were similar to the Boeing 707, no prototype Boeing 720 was built; any different systems were tested on theBoeing 367-80.[9] The first 720 took its maiden flight on November 23, 1959.[6] The type certificate for the 720 was issued on June 30, 1960. It first entered service with United Airlines on July 5, 1960;[6] 65 of the original version were built.[10]
The 720B version of the 720 hadJT3D turbofan engines,[6] producing 17,000 lbf (75.6 kN) each.[7] The JT3D engines had lower fuel consumption and higher thrust.[11] 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 withAmerican Airlines in March 1961;[7] 89 720Bs were built,[10] in addition to conversions of American's 10 existing 720s.[12]
As a modification of an existing model, the 720 had minimal research and development costs, which allowed it to be successful despite few sales.[13] The company built 154 Boeing 720s and 720Bs from 1959 to 1967.[2] The 720's wing modification was later added on the 707-120B and on 707-120s retrofitted to the B standard.[14]
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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 8 ft 4 in (2.54 m) shorter in length,[5] and had a lighter structure through use of lighter forged metal parts and thinner fuselage skins and structures.[13]
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.[13]
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.[15][16] This glove reduced the drag of the wing by decambering the root, which reduced the "middle effect", thereby increasing the effective local wing sweep. The wing root glove reportedly increased thedrag divergence Mach number of the wing by Mach 0.02.[17]
Though initially fitted with turbojet engines, the dominant engine for the Boeing 720 was thePratt & 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.[11]
Like the 707, the 720/720B used engine-driventurbocompressors to supply high-pressure air forcabin pressurization. The engines could not supply sufficientbleed 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 (number 4 engine) helps spotters distinguish 720/720Bs from most 707s, which had three turbocompressors.
The Boeing 720 lacked anauxiliary power unit, and relied 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 three (inner starboard) engine first, then disconnect ground power and air. With one engine running, bleed air from that engine could be used to provide necessary air pressure to start the other engines one by one. On ground, with ground starting crew at hand, all four engines were usually started with ground crew help: this was more reliable and faster.
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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[10] on the Los Angeles-Denver-Chicago route. American Airlines followed by putting the 720 in commercial operation on July 31 that same year. On January 2, 1962,Pakistan International Airlines′ first Boeing 720B – a Boeing 720-040B (registration AP-AMG) piloted byCaptain Abdullah Baig and copilot Captain Taimur Baig – set a world record during theLondon-to-Karachi leg of its delivery flight toPakistan for speed over a commercial air route, making the flight in 6 hours 43 minutes 55 seconds at an average speed of 938.78 km/h (583.33 mph).[18][19]
The 720 was supplanted by theBoeing 727 in the mid-1960s in its medium-range, high-performance market.[5] In the late 1960s, 720 and 720B aircraft were used by the US military to shuttle troops to the Far-East war efforts. The interiors of these planes were stripped of class partitions. Some of these flights originated atTravis AFB California and flew nonstop to Japan. At least one of the landing sites wasYokota AB, Japan, before the troops traveled to their final destinations.
After disposal of 720s 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 atEdwards AFB as a part of theFAA andNASAControlled Impact Demonstration program. The test provided peak accelerations during a crash. The performance of fire-retardant fuel was also tested.[20]
The first 720 (N7201U) was later renamed "The Starship" and became a private charter jet used mainly by touring rock bands. Its main user wasLed Zeppelin in the 1970s. The seating capacity was reduced and a bar with a built-in electric organ was added, along with beds, a shower, a lounge area, a TV, and video cassette player.[21]
Honeywell operated the last Boeing 720 in the United States, flying out ofSky Harbor Airport inPhoenix. 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.[22] Honeywell replaced their aircraft with aBoeing 757.
Pratt & Whitney Canada (PWC) operated the last flying 720 (C-FETB) until 2010. C-FETB was built as N7538A in 1960 and was initially flown byAmerican Airlines and later by Middle East Airlines as OD-AFQ. It was purchased by PWC in December 1985 and between October 1986 and January 1988 it was modified for use as a flying engine test bed. Internally it was known as FTB1 (Flying Test Bed 1). C-FETB was used to test a variety of engines with it being capable of carrying a largeturbofan in place of the right wing's inner engine. Alongside this a small turbofan could be mounted on the right side of the front fuselage while aturboprop could be mounted in the modified nose.[23] Its final operational flight occurred on September 29, 2010.[24] Pratt & Whitney Canada replaced the testbed with aBoeing 747SP.[4] In May 2012, the former PWC 720 was flown toCFB Trenton, Ontario, to be put on display at theNational Air Force Museum of Canada.[25]
The Boeing 720 was operated/leased by 57 different airlines[citation needed]. These operators flew Boeing 720/720Bs (● = Original Operators):
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.[46]
The worst of these accidents were:[46]
General characteristics
Performance
Related development
Aircraft of comparable role, configuration, and era
Related lists
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).
