Why Do Boeing Plane Models Start & End With The Number 7?

An aircraft’s identifying number helps engineers to differentiate between various products in the Boeing portfolio

The names of American manufacturer Boeing’s commercial aircraft are known for beginning and ending with the number seven. Starting with the 707 in the 1950s

Boeing has decades of developing popular jetliners with catchy-sounding numerical designations under its belt that generally follow the ‘7X7’ pattern. But what is the reason for this numbering system? Let’s take a look and find out.

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Theories about Boeing numbering

There are a handful of interesting theories that have surfaced regarding Boeing’s numbering system. For example the University of Houston notes that the numbers 7 0 and 7 are familiar to engineers the world over as the first three digits in the sine and cosine of 45 degrees. Given the 707’s angled wing sweep some thought that the name could refer to this but in reality the sweep is only 35 degrees.

Another perhaps slightly more optimistic idea is that 707 represented the number of passengers it carried. As the Sydney Morning Herald notes this presumably stems from Airbus having named its A300 after its approximate capacity which in reality went as high as 345. However this was not the case for the Boeing 707. Even at its exit limit the largest variant (707-320C) held just 219 passengers.

With both of these theories while interesting and understandable being incorrect this begs the question as to what the actual reason is for Boeing’s 7X7 numbering system. As it happens the matter is a rather straightforward affair.

The real reason

The logic behind Boeing’s numbering system ultimately boils down to ease of reference. An aircraft’s identifying number helps engineers to differentiate between various products in the Boeing portfolio. As Aero Time notes Boeing has historically always named its aircraft sequentially and its full designations are as follows.

• 100 for earlier models. Boeing no longer utilizes this designation but did retrospectively for the very first biplanes that it built.
• 200 for early single-wing designs that deviated from the contemporary biplane trend.
• 300 and 400 for commercial propeller-driven aircraft (as well as the 367-80 jet which ended up being the prototype for the 707).
• 500 for turbo-engine aircraft.
• 600 for missiles and rocket-powered devices.
• 700 for jet-powered commercial aircraft.
• 800 is presently unused.
• 900 for boats. Boeing once constructed a turbojet hydrofoil which it designated as 929.

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It is worth noting that there was once technically another series in the US manufacturer’s portfolio of commercial aircraft known as the Boeing 2707. This was a proposed American competitor to the supersonic European airliner Concorde. However Boeing never ended up producing this aircraft on a commercial scale.

Why do 700 series aircraft also end with a 7?

A second question to the above is why the company’s 700 series commercial aircraft also have to end with a seven. After all how different would the world be if airlines had flown thousands of passengers across the Atlantic on Boeing 740 aircraft every day? Does a Boeing 780 Dreamliner sound more or less dreamy?

Hopefully these examples show why Boeing made the change. From a marketing perspective it is more attractive on paper to have the symmetry of 7X7 rather than the formulaic but asymmetrical 7X0. In spoken discourse it also rolls off the tongue nicely and is easier for even non avgeek passengers to remember designations of legendary aircraft such as the iconic Boeing 747.

With the 707 having been such a success Boeing chose to persist with this numbering system. Of course there has been an exception to this rule over the years. Going back a few decades you may remember that Boeing also produced an airliner that it designated as the 720 model. Aero Corner notes that this was a modified version of the 707 and the type was designed to be able to operate from smaller airports.

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Conclusion Possible future designations

Going forward it is interesting to consider how Boeing might number its commercial aircraft in the future. After all the company appears to have somewhat backed itself into a corner by developing so many jetliner families over the years that all follow the same 7X7 pattern. The numbers it has already deployed are as follows.

• 707 717 727 747 & 757 have been discontinued.
• 767 remains in limited cargo production.
• 777 and 787 are new enough that they will continue to have more versions built such as the 77X.
• 737 will also likely be around for a while. Interestingly it has gone through all the sub-variants from -100 to -900 hence the newest series is referred to as the MAX.

Therefore as it stands the only number that is still available is 797. Interestingly enough this has long been rumored to be a new middle-market aircraft. Beyond that Boeing has no more numbers that will fit in with its current trend.

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In the future it may need to add a fourth number to the front of its designation like with the proposed Boeing 2707 in the 1970s. Alternatively it could move beyond a seven at the end of the number to give titles such as 748. It may even find that it has to move up to a new series such as the presently unoccupied 800.

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