The four-engined 707 was Boeing’s long haul masterpiece and entered service in 1958. With the market for jet transports linking major cities of the world sewn up, Boeing shifted its attention to the next market segment, short and medium haul flights between smaller cities. By shrinking the 707, they added a new type to their product line – the 720. It was the first jet to serve many of the ports it served, and for seven of the sixteen customers that bought 720s new, it was their first turbine powered aircraft.

The Boeing 707-120 Stratoliner first flew December 20, 1957 and entered service with Pan Am on October 26, 1958. The stretched Boeing 707-320 Intercontinental first flew January 11, 1959 and entered service with Pan Am on August 26, 1959.

the first Boeing 720

Meanwhile as early as 1956, studies began to address the next market segment, short and medium haul between second tier cities. Under the designation of the 707-020, ten configurations were considered, mostly with four engines, and some twin-jets. The most promising twin was the 707-020-6, which was 6 feet (1.83 metres) shorter than the future 737-200 but with nearly twice the wing area and a large tail.

In July 1957 Boeing chose a four engined configuration intended to carry up to 130 passengers on routes up to 1,700 miles long, using an airframe with the exact exterior dimensions of the 707-120 Stratoliner, but with significant structural changes which reduced the gross weight by 62,000lbs (28,122kg) from 247,000lbs (112,037kg) to 185,000lbs (83,915kg), although no orders were yet placed. As well as the Pratt & Whitney JT3 turbojet, additional engine options were GE’s J79 and Rolls-Royce’s Avon 26.

Finally the design was frozen on a configuration that shrank the 707-100 by 8 feet, but retaining the 707’s 130 foot wingspan. A fiberglass “glove” was fitted to the leading edge between the fuselage and the inner engine pylon, which increased cruising speed slightly and assisted in field performance. Leading edge flaps were fitted to the full span of the wing, reducing landing and takeoff speeds by 10 mph, and on approach, the aircraft flew with a more nose-up attitude. Other modifications, mostly involving reducing airframe weight, included thinner fuselage skin and smaller wheels on the undercarriage. The engine option was standardised on the Pratt & Whitney JT3-C.

TWA and Delta had both ordered Convair’s CV-880 jet for their short and medium haul routes, and with United about to place an order for 30 CV-880s, Boeing couldn’t stand to see another big order slip away, so they formally launched the 707-020. However, United’s president William A. Paterson didn’t want to be seen to be backtracking on his commitment to the DC-8, and requested a name change – the Boeing 720 was born.

N7201U rolled out of the hangar on October 30, 1959 and took to the air on November 23, 1959, commanded by Tex Johnston with Lew Wallick in the co-pilot’s seat. The second 720, N7202U, got airborne on January 8, 1960. Tests included maximum gross weight takeoffs and landings, stalls at every weight and configuration, and flutter tests. Speeds of up to Mach 0.95 were flown. The certification process with the FAA began on January 18, 1960. The third 720 to fly, N7203U, joined the programme in March.

At Boeing Field in a short-field landing test, N7201U, weighing 135,000lbs (61,235kgs) and with a 6mph tailwind, cleared a simulated obstacle of 50 feet off a steep approach and came to a full stop within 2,200 feet (670 metres). Because the intention was to bring jet service to smaller fields for the first time, the 720 was intended to routinely operate in and out of runways of 5,500 feet (1,676 metres).

The prototype 720 in flight in the midst of the test programme

One of the 720s went to Edwards Air Force Base in the California desert for aborted takeoff test runs, including fourteen “accelerate-stop” tests where the aircraft was accelerated to 165mph (266kph) before the throttles were slammed shut and braking began. Two tests were performed at an all-up weight of 230,000lbs (104,326kg), 13,000lbs (5,900kgs) above max gross weight. No tires burst in any of the tests.

N7201U was released to United Airlines for crew training on April 28, 1960, in anticipation of entry into service in early summer. After a five month test programme with the three 720s flying a total of 442 hours including 148 hours specifically for certification with FAA inspectors present, the type was certified for public transport service on June 30, 1960.

INTO SERVICE

United operated the world’s first revenue service by a 720 on July 5, 1960, when N7201U, configured with 44 first class and 53 coach seats, flew from Los Angeles to Chicago via Denver. Three days later Los Angeles to Seattle via Portland was opened, followed by service to San Diego and Las Vegas.

United’s first 720 is prepared for delivery at Boeing

American Airlines followed on July 31, 1960 with “Jet Gateway” service out of Cleveland to Los Angeles via St Louis. New York to Chicago saw its first 720 on August 14, extending from Chicago to Phoenix and on to San Diego on August 27. By the end of summer 1960, New York – Chicago was running five times a day in both directions. American were happy with their 707s so their 720s were branded the “707-023 Astrojet” (23 was AA’s Boeing customer code).

Engine technology was advancing at a fast rate and Pratt & Whitney evolved their already successful JT3C turbojet into the JT3D turbofan, which was quieter, more efficient and more powerful, especially at low speeds.

Boeing offered the new engine option for aircraft on order, as well as conversions for existing JT3C powered machines. Turbofan equipped 707s and 720s were suffixed with a “B”, creating the 707-120B and 720B. Pilot feedback said the new powerplants was like adding a fifth engine. 

American Airlines was an early adopter of turbofan engines, and announced they would convert all fifty of their Boeing jets – in service and on order – to B standard. Their N7537A was the first 720B to roll off the line at Renton and was used to certify the new variant, first flying on October 6, 1960. It logged 60 hours of test flying with Boeing before beginning the FAA certification process in December at Edwards which involved more “accelerate-stop” exercises, often at weights in excess of the maximum certified weight. In early February 1961, American’s third 720B performed 103 route-proving flights around the USA including high altitude work at Colorado Springs up in the Rocky Mountains, snow and ice encounters in New York, Kansas City and Omaha, and the heat and humidity of Miami. The last test was performed for the FAA on February 23 1961 and the 720B was certified the following month.

An American Airlines 720 Flagship in flight

Of the sixteen airlines to buy 720s new, Irish flag carrier Aer Lingus was one of the seven for whom the type was their first turbine equipment. Aer Lingus’ transatlantic routes were shorter than most, heading out from Shannon to Boston and New York with flying times sometimes as short as four hours, making the medium-hauler a better choice than the larger, more expensive 707. Their first aircraft was handed over to the airline on October 14, 1960 and went to Tucson Arizona where it spent the next eighteen days flying round the clock to train Ireland’s first fourteen jet pilots. EI-ALA entered service on the Dublin-Shannon-New York service on December 14, 1960, with Dublin to London starting in early 1961.

Aer Lingus loved their lightweight 720s for their short Atlantic crossings

Braniff International ordered only five 720s to augment their 707 fleet, and entered service on February 20, 1961 flying Chicago – Dallas – San Antonio. Their second aircraft entered service April 30, and opened up service on the multistop Minneapolis – Kansas City – Dallas – San Antonio – Mexico City run.

The FAA took delivery of their own 720, N113, built to Braniff specs, on May 5, 1961, mostly to train safety inspectors, who needed, in the FAA’s own words, “Skill in aircraft equal to that of the airline pilots whose operation they monitor.” This was the only 720 to never carry passengers.

Western Airlines had been resistant to pure jets – “Would you buy the Queen Mary to sail across Lake Tahoe?” asked CEO Terry Drinkwater, but the prospect of Hawaiian service changed his mind, and Western began 720 service on May 15, 1961 from Los Angeles to Mexico City; on June 1, they began three daily flights from Los Angeles to Seattle (one nonstop, one via San Francisco, one via Portland).

The first non-US carrier to begin 720B service was West Germany’s Lufthansa, who kicked off on May 20, 1961 with an exotic run to South America, routing Frankfurt to Santiago de Chile via Paris, Dakar, Rio, Sao Paolo, and Buenos Aires. July 1 saw the start of 720 service to Tehran with stops in Vienna, Rome, Beirut, Cairo and Baghdad.

Northwest began 720 service from Minneapolis to New York on July 1, 1961 and soon expanded service including intra-Asia flights out of their Tokyo hub.

Eastern Air Lines introduced the first of fifteen aircraft with service from New York to Miami via Jacksonville on September 24, 1961, and to Fort Lauderdale on October 1, with their “Golden Falcon” service.

Sanctions-busting turbojet 720s served Air Rhodesia (and later, Air Zimbabwe) were all ex-Eastern Airlines machines

High altitude airports in the 32,000-mile route network of Colombian flag carrier Avianca such as Quito (9,220 feet) and home base Bogota (8,260 feet) made the hot rod 720B a natural choice to be the airline’s first turbine-powered hardware, first appearing on the route from New York – Montego Bay – Kingston – Bogota on November 24, 1961.

While waiting for the first 720 delivery, Continental’s existing fleet of 707s was worked so hard that N70773 was the first Boeing jetliner to clock up 10,000 hours. The first 720 delivery took place on April 30, 1962; however the period turned out to be a tragic one for the airline as on May 22 a 707 was blown up in midair by a suicide bomber for insurance (the tragedy was the basis of the plot of the bestselling novel and box office blockbuster Airport) so the 720s were rushed into service on routes from California to Texas and Chicago, then Dallas – Midland/Odessa – Albuquerque – Denver, followed by Amarillo, Phoenix, El Paso and Tucson as more frames came into service and the capacity squeeze on the rapidly-expanding carrier began to ease.

El Al operated two 720Bs starting in April 1962 from Tel Aviv to European ports as well as a long haul route to Johannesburg via Tehran, avoiding airspace of unfriendly nations, which meant a sixteen hour trip with two complete crews on board and twenty-five course changes along the way.

Ethiopia’s high altitude capital Addis Ababa 7,500 feet above sea level made the sporty 720B a perfect introduction to jet service for Ethiopian Airlines. Their first two machines were flown together from Seattle via New York, Madrid, Athens to Addis and arrived on December 3, 1962. Inaugural service took place on January 15, 1963, Addis – Asmara (Eritrea) – Nairobi; the next day the return flight continued northwest out of Ethiopia to Athens and Madrid.

Another exotic carrier for whom the 720 was their first turbine equipment was Pakistan International Airlines (PIA), who began jet service on February 12, 1962 twice weekly from Karachi to London via Tehran, Geneva and Frankfurt; and twice weekly via Tehran, Beirut and Rome. Twice weekly service soon followed to Dhaka (then the provincial capital of East Pakistan which would later separate to form Bangladesh). In April 1962 London service extended to New York, and Moscow was added.

After intensive crew training by TWA at Kansas City, Saudia began jet service with a 720 flight on the busy route from Jeddah to Beirut on March 15, 1962. Riyadh, Dhahran, Cairo and Bombay soon followed.

The last carrier to place new 720s into service was plucky little Pacific Northern Airlines based up in Anchorage, who put the first of their two machines into service on the run down to Seattle on April 27, 1962, followed by service to Ketchikan and Juneau.

GOLDEN YEARS

As 720s continued rolling off the line at Renton, the initial operators expanded service. By 1962 United served twenty-five cities with their 720s, including nine flights a day in the busy San Francisco-Los Angeles market. The last non-fan 720 at American was converted and returned to service as a B model on February 1, 1962 and the fleet grew to 25 machines. Western kept adding new planes in small batches until the fleet grew to twenty-seven, including the 154th and last 720B built, delivered to Western on 8 September 1967. At one point their entire fleet was standardised on Electras and 720s.

TWA leased four Northwest 720s to begin service with N792TW from New York to Kansas City on July 22, 1962. However the lease was short-lived and TWA standardised on the 707 and returned the four 720s to Northwest by the end of October.

Lufthansa used six of the type on its short haul European network, and to add capacity to New York in summer 1962 with a stop in Shannon. October 3, 1962 marked the introduction of a new stopping service across Asia, routing Frankfurt – Munich – Rome – Cairo – Dhahran – Karachi – Calcutta – Bangkok – Hong Kong. In April 1965 Lufthansa inaugurated Sydney via Athens, Karachi, Bangkok, Singapore and Darwin. European destinations included Vienna, Madrid, Barcelona and Las Palmas. They were sold in pairs to Pan Am; the last one departed in February 1966.

Pan Am, who ordered over 100 707s, never bought 720s from Boeing but bought three ex-American machines as well as the six Lufthansa to operate shorter international services to the Caribbean and Central America until the early 1970s.

PIA made history on April 29, 1964 by becoming the first non-communist airline to operate to China, routing Dhaka (then part of Pakistan) – Guangzhou (then Canton) – Shanghai using 720s. They added six secondhand 720s as the decade wore on, five from Western and one from Alia / Royal Jordanian. They flew their 720s right up to the end of the 1980s.

A notable incident in Western Airlines service began on June 2, 1972, when a Vietnam vet and his girlfriend hijacked a 720 and after letting off half the passengers in San Francisco, and stopping in New York to pick up fuel and a navigator, flew across the Atlantic to Algeria where they were granted political asylum. This remains the longest-distance hijacking in American history.

Western Airlines joined the jet age with the 720

The 1970s saw most of the initial customers begin to sell their fleets. United and Eastern never converted their 720s to B models, and began to retire them around the turn of the decade. A few went to travel clubs and charter operators such as Trans Polar and AeroAmerica, who grew their turbojet fleet of 720s to eleven aircraft for a mix of charter operations including holiday flights in Europe out of a hub at West Berlin, and scheduled flights such as Seattle to Spokane, until they shut down in 1982. Alaska Airlines bought the three Pacific Western 720s and one from United for some interim capacity, parking the fleet in 1975.

Six of the turbojet United fleet went to a Miami-based start-up, Air Belize; three were all-economy 132-seaters and three freighters. The operation ended in 1980 and one, N64696, became a Miami fixture, parked in the front yard of the George T. Baker Aviation School for student mechanics to tinker with until it was scrapped in 2000.

Air Belize monogrammed service items turned up in Miami flea market in the years after the shutdown

Another second home for turbojet 720s was the Dominican Republic – Aeromar flew two on passenger services, as did Aerovias Quisqueyana until 1977 and Hispaniola Airways flew from Puerto Plata to Miami and New York until 1984.

Some turbojet 720s found work with European carriers, such as Calair in Germany, and Conair of Scandinavia who took five each from Eastern.

The 720Bs with turbofans found second careers at better-known airlines – Greek flag carrier Olympic Airways took seven from Northwest for its European network from 1972 until 1980, Somali Airlines took three from Lufthansa for its base in Mogadishu, and Air Malta leased and later bought two PIA 720Bs, adding six from Western, flying right up to October 1989. Ariana Afghan operated one ex-Pan Am aircraft from April 1972 until 1980 out of Kabul on multi-stop services to Europe.

Ariana Afghan had a solitary 720 up until the 1980 Soviet invasion

British charter carrier Monarch Airlines operated seven 720Bs between 1974 and 1983 – five ex-Northwest and a pair from American. Danish holiday airline Maersk also flew five ex-Northwest 720Bs until 1981 when they migrated to Conair to replace their less efficient fleet of five ex-Eastern 720 turbojets.

The biggest operator of second-hand 720s was Middle East Airlines of Lebanon, who operated twenty-one 720Bs over thirty years; eleven (more than half) were destroyed by war. Their odyssey began with the short-term lease of three Ethiopian Airlines 720s in 1966. American sold nine -023Bs to the Beirut-based carrier in 1969, followed by four more, the last arriving in May 1973. Three -047Bs from Western were bought in 1974, bringing the fleet to sixteen. Once the Lebanese civil war started in 1975, the number started to drop, beginning with the tragic bombing of OD-AFT on New Year’s Day 1976 over Saudi Arabia en route to Dubai, then OD-AGE was wrecked when it was hit by a shell on June 27 while parked. The two lost aircraft were replaced by a pair of -047Bs from Western Airlines and an uneasy peace settled on the capital for the rest of the 1970s, until OD-AFR was destroyed by a dynamite bomb shortly after landing back at Beirut from Tripoli (Libya) in 1980.

MEA 720 on the ramp in Beirut

Israeli fighter jets destroyed four 720Bs (and a pair of 707s) on the ground in June 1982, and one more in August. In August 1985 two 720Bs were destroyed by shelling of MEA’s parking area. Hostilities around the capital of Beirut became so bad in the late 1980s that air travellers from the east side of the city were unable to reach the airport by surface transport, so MEA opened up a twice a day rotation to Kleyate, sixty-one miles away, using their 720s, to feed traffic to their international network that would normally have arrived by private car and taxi.

The Lebanese civil war ended in 1991 and regular 720 operations came to an end around the same time, although the type was active for crew training and ad hoc equipment substitutions. Two aircraft, OD-AGB and –AFM, were returned to service in June 1994 as post-war traffic levels increased dramatically (-AGB, built in 1960, was at the time was the oldest flying jetliner in the world). These two brave soldiers finally left Lebanon in December 1995 for new lives at Pratt & Whitney Canada as flying test beds.

Pratt & Whitney’s flying test bed was the last active 720

On a happier note, 720s were used by many rock bands in the 1970s. Best known was Starship I, ex-United -022 turbojet N7201U that had $1 million spent on its forty-seat VIP interior in 1973 before flying the likes of Led Zeppelin and Elton John around the US on concert tours. Led Zep later chartered Ceasars Chariot N7224U, another pimped-out 720 with a similar provenance which saw service with the Bee Gees the following year.

Five 720s passed through the hands of McCulloch Corporation, who used the aircraft to fly potential buyers to see land sites for sale in Arkansas, Colorado, Nevada and Arizona throughout the 70s. For extra revenue they did the occasion charter for NASA, sports teams and rock bands.

Saudi Prince Nawab Bin Abdul Aziz acquired an Western -047B in 1978 for his own private transport; in 1980 it was obtained by Sheik Kamal Adham. In 1988 it was sold to JAR Aircraft Service and flew VIP charters out of Beirut until the early 2000s and remains parked in Malta to this day.

Taiwan, aka the Republic of China, used ex-Northwest Orient -051B as a head of state transport, with its serial number 18351 becoming its military registration, from December 1971 until February 1996.

Several 720s were used as flying testbeds. Allied Signal, later Honeywell, flew an ex-Northwest -051B out of Phoenix Sky Harbor from 1987 until July 2008 and was used for testing and certification of several engine projects. Boeing repurchased two 720s – one turbojet -025 from Trans Polar in 1972 to develop anti-submarine warfare technology which was parked in 1979, and an -051B from Conair in 1987 to trail missile warning systems, high accuracy navigation systems, and electronic warfare systems, until it was parked in 1992.

Hughes Aircraft bought a 720 from Ethiopian Airlines in 1989 and converted it to a flying laboratory for acoustic emissions tests known as the Advanced Infrared Measurement System, before being handed over the US military to join the Defense Advanced Research Projects Agency (DARPA) from 1993 until retirement in 1998.

The most spectacular experimental use of a 720 was the sacrifice of the FAA’s own N113 in a remote-controlled crash in the California desert on December 1, 1984. The intention of the project, called the Controlled Impact Demonstration, was to study the effectiveness of a fuel additive which it was hoped would inhibit ignition in a crash, and also to investigate the crashworthiness of aircraft seats and structure.

During the final approach, the aircraft got low and slow, and began a diverging rolling motion. Since the data acquisition systems had been activated, the flight was committed to impact, which was more violent than intended. Number three engine exploded and the cabin was ruptured by posts cemented to the runway to simulate obstacles encountered in an off-airport crash scenario. The massive resulting fire represented a significant setback for the experimental fuel but the data collected on crash survivability was deemed a success and just as important.

720 crash test

Pratt & Whitney Canada acquired OD-AFQ from MEA in 1986 and reregistered it C-FETB for use as a flying test bed for their aircraft engines, with a second machine, OD-AGB, coming from the same source in 1995. Two others were acquired to be scrapped for parts to sustain the programme, which provided air tests for many Pratt engines including the PW307A, PW308, PW545 and IAE V2500.

The 720 era, which lasted fifty-two and a half years, came to an end on May 9, 2012, when Pratt & Whitney delivered C-FETB to Canada’s National Aviation Museum at CFB Trenton. Other 720s on display are the Taiwanese head of state aircraft at Kansghan AFB near Koahsiung, an Avianca machine at the Childrens Museum of Bogota, and PIA have kept one of their fleet at their Planetarium in Lahore.

While the 720 was only ever intended as a stop-gap before the advent of dedicated short and medium haul machines such as the 727 and 737, the type was the first jet at many airports and over half of its customer airlines, and went on to serve hundreds of airlines and millions of passengers for over half a century – a remarkable achievement for the baby of the 707 family.

Ecquatoriana’s 720s were the most colourful in the 70s skies