Since 1954, the year of the construction of their first jetliner prototype, Boeing has decided to name their line of commercial jets with the code “7×7”. This naming convention was adopted after WWII to arrange their line of products in specific segments.
Plus, 7 is a lucky number and sounds excellent for marketing purposes (Seven-Oh-Seven, Seven-Three-Seven, Triple Seven…). The first one was the 707, a four-engine narrow-body powered by 4 Pratt & Whitney JT3D, that started a streak of lucky projects commercial-wise, especially the 737 series, the 777, and the innovative 787 series. But there is a jet plane that it’s one of the black sheeps for Boeing, and it doesn’t even follow the naming convention: the Boeing 720. Let’s take a look at this very peculiar jet, shall we?
In order to be able to talk about the 720, we have to talk about the 707 first, because both aircraft are similar.
Named by the pilots “the Slush Bucket”, the 707 began the fortune for Boeing when it entered service on October 26th, 1958 with PanAm, making the world a more connected place thanks to its speed (Mmo of Mach 0.80), long-range (3300nm) and average passenger capacity of 139. According to the Britannica Online Encyclopedia, the plane could connect New York to Paris in 8 hours and 41 minutes with only one stop in Gander, at the time a strategic airport for refuelling before “Crossing the Pond” (The Pond being the Atlantic). After PanAm, in the next years, 856 more airplanes of this model were built for hundreds of airlines on every single continent, the most famous one being the N707JT, owned by Hollywood star John Travolta until 2017.
Following the success of this airframe, Boeing has gone on thinking about dominating the domestic U.S. market with a plane that could land at smaller fields and be profitable at shorter distances, without building a new airframe from scratch.
So the modest era of the 720 begins
The task was not easy, so they decided to create a 2.7-meter shorter version of the 707, the Boeing 720, which entered service in 1961.
Two versions of this bird were created: the normal 720, with a range of 2,700 nm, pax capacity of 131 people and powered by JT3C engines, and the 720B, with a range of 3,200nm, pax capacity of 156 and powered by JT3D engines. A total of 154 airframes of this model were built and they entered service in 32 countries and a little less than 60 airlines, modest numbers, considering the success of future Boeing planes.
The main characteristics that set the 720 apart from the 707 are the same which makes the aircraft ideal for the aforementioned purposes: lighter fuselage and lower fuel capacity, increased cruise and takeoff performance, and high profitability in domestic markets.
On the other hand, the 720 was a very popular private jet, used by organizations and music bands all over the world. The first one ever built, N7201U, was used by the rock band Led Zeppelin to tour the world in the ’70s. Plus, it was also used by NASA for some experiments.
Why so little success?
The reason for the 720 being the least ordered Boeing jet plane is soon to be said: some other planes were able to fill the niche of short/medium-haul domestic jetliners better than the 720 itself. For example, the Vickers VC10, the Hawker-Siddeley Trident, and the DeHavilland DH106 Comet were better in everything than the 720: better fuel economy, fewer maintenance costs, and more optimized cost per seat performance. Moreover, Boeing itself cannibalized the plane by creating, in 1963, the 727, which had all of the aforementioned perks and one engine less to maintain. Then came in 1967 the 737, which didn’t require a flight engineer at all and had only two engines.
The Boeing 720 can be considered for the 707 what the 747Sp was for the 747 family: a failure in commercial scheduled operations with moderate success as a private jet and as a scientific testbed. The very last flight of the 720 was flown in May 2012 to Canadian Airforce Base Trenton, Ontario, to be put on display at the National Air Force Museum of Canada. Other planes of this model can be observed in various museums in Taiwan, Pakistan, and Bogotà.