Just two years after Boeing delivered its first 737 airliner, orders were so poor that the company seriously considered shutting down production of the twin jet.
How serious an error that would have been was boldly illustrated Wednesday as Boeing delivered its 8,000th 737, a Next Generation 737-900ER to United Airlines.
United was the first American customer for the 737 in 1968. Boeing considered halting 737 production in 1970 when it received just 37 orders for the plane.
Now Boeing is producing the popular single-aisle airliner at a record pace, 42 planes a month, at its Renton plant. And it plans to ramp that production pace to 47 aircraft monthly by 2017.
The 737 is by far the most popular jetliner that Boeing or any other aircraft manufacturer has ever built. Boeing has seen customers order nearly 11,800 of the planes.
Just how popular is the 737? Compared with other planes that were considered major commercial successes, 737 production numbers are many times theirs.
Boeing's three-engine 727, once the most popular jet airliner ever built, had a production run of 1,831 planes. The plane that gave birth to popular passenger air travel, the Boeing 707, sold 1010 commercial examples.
The world's first jumbo jet airliner, the Boeing 747, has generated 1,538 orders. Boeing's most popular widebodied jet, the twin-engine 777, counts 1,548 orders and deliveries.
Other aircraft makers' jets were far less popular than the 737. Douglas sold just 556 of its DC-8s. Lockheed produced just 250 of its three-engine L-1011.
The closest competitor to the 737 is Airbus's A320 family of single-aisle jets. Airbus last year delivered the 6,000th example of the A320.
But some aerospace analysts are predicting that the A320 may someday surpass the 737 in total orders unless Boeing begins selling its newest member of the 737 family, the 737 Max, at a quicker pace.
The first 737 Max is expected to go into service with Southwest Airlines in 2017. The Max has improved engines and aerodynamics for better fuel economy.