707, 727, 737, 747, 767, 777, 787. Even for people who aren’t crazy about airplanes, those numbers are instantly recognizable as types of Boeing commercial airliners. But why did Boeing adopt that numbering system?

Pan Am Boeing 707-321B (Mike Freer via Wikimedia Commons)

Ever since the Model 1, Boeing, along with most aircraft manufactures, used sequential numbers to identify their aircraft (military aircraft received separate designations). At the end of WWII, Boeing was mainly a builder of military aircraft, but the company knew they would soon be diversifying into commercial aviation, missiles and even spacecraft. They needed a system that would easily identify their products and what they were made for. So they started using numbered sets of 100 to differentiate their endeavors: 300 and 400 was used for aircraft, 500 for turbine engines, 600 for rockets and missiles, and 700 for commercial airliners.

A Boeing KC-135A, known to Boeing as the Model 717, refuels a Boeing B-52D Stratofortress (US Air Force)

When Boeing developed the Model 367-80, better known as the Dash-80, as an aerial tanker for the US Air Force, they knew that it would be spun off into a commercial airliner. Since “Model 700” didn’t have much of a ring to it, they went with the catchier 707. The Air Force tanker, which was known in military parlance as the KC-135, received the internal Boeing designation 717.

Boeing 727-30C of Lufthansa (Steve Fitzgerald via Wikimedia Commons)

It only made sense, then, that the next airliner would be the 727. That designation went to the trijet derived from the 707, and was followed by the 737, which went on to become the most popular airliner in the world. The 747 jumbo jet was the world’s first wide body, and was followed by the narrow-body 757, wide-body 767, and globe-spanning 777. Boeing made the world’s first foray into composite construction with the 787, and currently has a new clean-sheet aircraft in the works which will reportedly be called the 797 intended to target the so-called “middle of the market,” airliners sized between the 737 and larger wide-bodies.

Boeing 717-2BD of Delta Airlines (AEMoreira042281 via Wikimedia Commons)

Since 717 was used as the designation for the KC-135, it never made it onto a commercial airliner until Boeing merged with McDonnell Douglas in 1997. At that time, the McDonnell Douglas MD-95, a derivative of the DC-9 series, was rebranded the Boeing 717 and entered service in 1999. The only other time Boeing didn’t use the palindromic numbering system was with the 707-020, a high-performance, short-range version of the 707 which was built in relatively small numbers and was branded as the 720.

So what happens after Boeing builds the 797? Back in the 1960s, the company started work on a supersonic transport that would have been known as the Model 2707. While that aircraft never progressed beyond the mock-up stage, that may provide a clue on what Boeing’s plans are for the future of the commercial airliner, and the future of their numbering system.

Boeing 720B of Middle East Airlines (Eduard Marmet via Wikimedia Commons)
Boeing 737-7Q8 of Southwest Airlines (Photo by the author)
British Airways Boeing 747-436 (Photo by the author)
Delta Airlines Boeing 757 (Photo by the author)
United Parcel Service Boeing 767-300F (Dylan Ashe via Wikimedia Commons)
American Airlines Boeing 777-223ER (Photo by the author)
All Nippon Airways Boeing 787-8 Dreamliner (Spaceaero2 via Wikimedia Commons)

Source: Boeing


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