For a half-century, Boeing Co. mechanics in a sprawling factory north of Seattle have riveted together aluminum panels into the familiar hump-backed form of the 747 jumbo jet. Test pilots then put each new plane through its paces on an adjacent air strip before sending it off to roam the globe.

This airplane, more than any other, made long-range travel into a mass-market phenomenon. And on Monday, one of the jets born here is returning home.

Delta Air Lines Inc. will fly a 747 filled with employees and customers from its Detroit hub to Boeing’s plant in Everett, Washington. It’s the first in a series of farewell flights to Delta hubs this week marking the end of the airliner’s U.S. passenger service. For those aboard, it’s a rare opportunity to touch down on the same runway from which the first 747 lifted skyward on Feb. 9, 1969.

On the ground, Boeing workers who helped build 747-400s like the returning Delta plane will celebrate an aviation milestone. But there’s poignancy to the moment: With just 14 unfilled orders in Boeing’s backlog, and four-engine aircraft appears to have fallen out of favor. The future isn’t bright for jumbo jetliners such as the old 747.For a morning, at least, Delta and Boeing will be setting aside their differences to bask in nostalgia. Just last week, Delta ordered 100 jets from Airbus SE, Boeing’s rival. And a trade fight between the U.S. planemaker and Bombardier Inc. threatens to foul up a separate deal that’s key to Delta’s fleet plans.

There will be those aboard Monday’s farewell-to-passengers flight who came of age with the 747. The planes’ hulking wings—and, for children riding on Pan Am in the 1970s heyday, those captain’s wing pins—symbolized access for millions of us to foreign lands not easily reached by telephones of the era. A generation came to learn the aircraft’s quirks, such as the jet’s bulbous nose and swept wings and the vibrations during the take-off roll that caused over-stuffed luggage bins to pop open on early models. There was also the fascination, never lost for some, of ascending a staircase to ride high above the world in the “bubble,” the deck behind the cockpit.

The 747 was the first twin-aisle airplane, with more than double the capacity of the largest commercial craft at the time. Delta’s 747s, introduced on a maiden voyage in 1970 from Atlanta to Dallas to Los Angeles, brought the first overhead luggage bins to the airline, as well as the first in-flight audio channels, dubbed “Deltasonic,” which featured the Beatles, Burt Bacharach and Beethoven. The planes could hold 370 passengers, including 66 in first class and six in those penthouse seats up the stairs.

The design made it literally a wide-body, which became a moniker for long-range aircraft. “It’s one of two seminal airplanes,” said George Hamlin, an aerospace consultant, a former airline and aerospace executive and an aviation history buff. The DC-3, the other iconic aircraft on Hamlin’s list, was a silver piston-engine made by Douglas that helped airlines evolve from mail carriers to people movers in the 1930s and 1940s.

But it was the long-haul capability—a 6,000-mile reach—that made the 747 transformational. “The range of the plane allowed it to go anywhere in the world,” said Michael Lombardi, Boeing’s corporate historian. “It was at that point in history where all of humanity had the ability to get on a flight.”

The peak year of the 747 came in 2002, when the airplane completed 33,000 flights hauling 10.5 million passengers on 50 airlines. All told, 1,540 Boeing aircraft have been delivered since 1969.

“It was the plane that shrank the world. That is the legacy of the 747,” Lombardi said. “Joe Sutter would tell you the same thing.”

The farewell tour for the Delta 747 also serves as an elegy for Sutter, who died last year at 95. The blunt, sometimes fiery tempered Boeing engineer was known as the “Father of the 747” for his role in shepherding the plane to market in the 1960s against steep odds. Juan Trippe, the autocratic founder of Pan American World Airways who was then the most powerful person in aviation, wanted a single-aisle design with two decks. Sutter believed that the configuration would doom the big plane, so he held out for the single-deck, twin-aisle design. His team, nicknamed the “Incredibles,” brought the plane to life in less than two and a half years, while dealing with balky engines and the prospect of financial collapse.

Boeing created the plant in Everett—the largest building on the planet by volume—just to build the 747, and the same facility eventually turned out such wide-body successors as the 767, 777 and 787 Dreamliner. Airplane sales were already slumping by the time the 747 debuted in the turbulent 1970s travel market, but Lombardi said the period proved fertile for Boeing’s development of next-generation improvements: cockpits operated by two pilots instead of three, flight computers and glass screens to replace anode dials.

Monday’s event in Everett actually marks the second time Delta has retired its 747 fleet. The Atlanta-based carrier took delivery of the first of five 747-100s in October 1970, a period when U.S. carriers were starting to experiment with wide-body jets on domestic routes. The planes featured a Delta “penthouse” behind the upper deck that could be reserved by private parties or by five or six customers who purchased seats together. Even with features such as “deep carpet, soft lights, patina of rosewood and walnut, stereo sound,” as Delta described the private lounges in a brochure, the new planes struggled to make money and were eventually returned to Boeing.

Boeing eventually created the best-selling 747 model, the -400, which was delivered first to Northwest Airlines in 1989. This started the fleet that would eventually become Delta’s when the airlines merged nearly two decades later. Delta retired the prototype on Sept. 9, 2015, after it had logged 61 million miles.

Delta became the last U.S. carrier to fly the passenger version of the 747 once United Airlines retired its jumbo fleet in November. Outside of the U.S., however, there will still be plenty of 747s carrying passengers: British Airways, Korean Air and Lufthansa are all big operators.

But over the past 10 years, sales of the latest Boeing 747 model have dwindled, and the jet’s future, to the extent that there is one, will be as a freighter, said George Ferguson, aerospace analyst with Bloomberg Intelligence. United Parcel Service Inc. holds all but three of the unfilled orders left for the 747, as well as options to order an additional 14 planes.

“It’s never going to be a big seller again, that’s absolutely done,” Ferguson said of the 747. “It can hang on for a while, but it’s a sunset.”