The Boeing 707 is often seen as having been the catalyst for the ‘jet age.’ This classic narrowbody quadjet was the American manufacturer’s first jet airliner. The 707 helped bring air travel to the masses following its launch in the late-1950s and was known for its long-range capabilities. However, a shorter-range variant was also developed, selling over 150 units: the lesser-known Boeing 720.
The beginning of the jet age
The world’s first jet airliner was the De Havilland Comet, which first flew commercially in 1952. However, it was not until the end of this decade that jetliners experienced widespread popularity. Indeed, the same can be said of commercial aviation itself. At the end of the 1950s, two American quadjet airliners were launched that would go on to revolutionize the airline industry, both technologically and socially. These were the Boeing 707 and the Douglas DC-8.
Pan Am launched the 707 commercially in October 1958. Delta and United did the honors for the DC-8 less than a year later, in September 1959. The two aircraft marked the advent of widespread commercial air travel, particularly in the long-haul market. It is no coincidence that 1958 was the first year that more transatlantic passengers flew than took the boat.
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Comparing the Boeing 707 and Douglas DC-8
In terms of specifications, there was not much to separate the two aircraft. Both types had four Pratt & Whitney JT3D turbofan engines, and a capacity of 140-150 passengers (depending on the exact configuration). However, comparing the 707-320B and DC-8-61 models, the 707 just had the edge in terms of cruising speed (Mach 0.89 vs. Mach 0.82). It also benefitted from a longer operational range (9,900km / 5,350 NM vs. 9,408km / 5,080 NM).
However, the story in terms of the two airliners’ commercial success has a greater contrast. While Boeing sold 1,010 707s, Douglas could only shift just over half of this figure, selling a total of 556 units. Among Boeing’s 1,010 707s were 154 examples of a shorter variant – this was known as the Boeing 720.
The Boeing 720
The Boeing 720 is, to date, the company’s only passenger jetliner that does not follow the ‘7×7’ naming trend. Boeing designed the 720 as a lighter version of the 707, which would allow it to offer greater versatility in terms of serving airports with shorter runways.
It was around 2.7 meters (nine feet) shorter than the original 707-120, with a significantly reduced range. The original 720 had a range of 5,200 km (2,800 NM), using Pratt & Whitney JT3C turbofan engines. However, a later variant, known as the 720B, could fly slightly further following the implementation of improved JT3D engines. The aircraft had a two-class capacity of 131-137 passengers, or 156 in a one-class configuration.
Successful despite lower sales
Although the 154 720s that Boeing sold only represented around 15% of total 707 sales, the type nonetheless proved profitable for Boeing. The reason for this was that, as a derivative of an existing aircraft rather than a new project altogether, it had relatively low development costs. Following its commercial launch with United in July 1960, the 720 enjoyed a service life that spanned more than half a century.
During this time, the 720 was more than just a passenger airliner. For example, 1984 saw a 720 partake in the FAA and NASA’s ‘Controlled Impact Demonstration’ program. In this test, a remote-controlled 720 was deliberately crashed to test safety technology such as fire-retardant fuel.
Engine manufacturer Pratt & Whitney Canada operated the final 720 as a testbed aircraft. This made its final flight in September 2010, bringing more than 50 years of varied service to an end for the type. PWC replaced the 720 with a 747SP – as a shortened variant, this is to the 747 what the 720 was to the 707. Two years later, the former PWC 720 flew to Trenton, Ontario, where it would be displayed at the National Air Force Museum of Canada. Several other examples of the 720 have also been preserved around the world.