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Editor’s note: This story has been updated with new information.

As discussed in an episode of “Have Points, Will Travel,” Ian Agrimis learned a subtle but important distinction in the airline world when he discovered that there’s actually a big difference between a “direct” flight and a “nonstop” one. Confused? Don’t worry, you’re not the only one.

While both options will get you to the destination printed on your ticket on a single airplane, a direct flight could actually take much longer than a nonstop one. That’s because direct flights can sometimes stop at multiple airports along their route, so long as the flight number stays the same.

For example, Singapore Airlines offers two options to get from New York to Singapore Changi Airport (SIN): a nonstop from Newark Liberty International Airport (EWR) and a direct flight from John F. Kennedy International Airport (JFK), with a pit stop at Frankfurt Airport (FRA).

The JFK-SIN flight is currently the longest in the world in operation, scheduled at just shy of 19 hours of gate-to-gate flying aboard an Airbus A350-900ULR across roughly 9,527 miles. Flying the nonstop will also generally cost you more — the only classes of service available on the A350 serving the route are premium economy and business. The A380 serving the route via Frankfurt has economy and first class.

Although the nonstop is certainly the fastest way to travel from the US East Coast to Singapore, the stopover, direct flight, still has some loyalists and upsides. For one thing, it features Singapore’s legendary first-class suites, but beyond that, on such a long journey, some travelers prefer to get a stretching break.

Before the 1980s, direct flights with stops were much more common. Getting to East Asia from the U.S. East Coast or Europe required stopping for fuel at least once.

“I’m old enough to remember I flew a DC-10 to Hong Kong: Geneva, Zurich, Karachi, Hong Kong,” said Guillaume de Syon, a professor of history at Albright College whose research includes aviation history. “I never got off the plane.”

Related: The world’s longest nonstop flights

De Syon said that before the 1980s, jet engines were not reliable or efficient enough to fly such long routes nonstop.

“There’s a technical shift starting in the late ’70s and definitely confirmed in the 1980s that the so-called direct flights are no longer necessary,” he said. “All of a sudden you’ve got better engines, longer ranges.”

Almost overnight, he said, nonstop routes like New York to Johannesburg, which had previously always required at least one technical stop, became possible.

Today’s jet engines are “much more reliable,” said Gregory Alegi, an aviation historian who teaches at Luiss University in Rome. “You can basically fly nonstop between two points anywhere on Earth,” he added. “You take it pretty much for granted that you can fly safely anywhere.”

The rise of nonstop flights and the introduction of longer-range midsize jets like the A321XLR means the whole shape of the aviation industry is changing, according to Alegi. Aside from fewer multistop direct flights, it also means connecting flights are slowly becoming less common.

“You can think, in Europe, of places like Amsterdam: It’s in a small country — a rich country, an advanced country, but with a very small local base. It thrives because people fly in there, change airplanes, and then go on to their final destination,” he said. “If I can fly direct from another medium-size city to my destination, then I’m going to skip Amsterdam.”

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For Alegi, though, there may always be a case for stops on ultra-long routes like New York-Singapore, even if they’re not technically necessary.

“Do you consider the stopover an inconvenience, which means you’ll take it only if the price is cheaper, or do you think it’s an advantage because you’re stopping in some place you want to be and you’ll take those six hours to visit the city?”

Alegi answered his own question: “I think the data shows that people want to go nonstop to a destination or stay over for a few days, rather than just doing it lightly over a few hours.”

Airlines are increasingly making stopover flights more flexible, allowing passengers to spend more time (think days, not hours) in the cities where they pause.

As stopovers and connecting flights become less common, Alegi also thinks airports may shrink in size and commercial scope.

“If there are fewer stopovers, if there’s less time to kill, maybe we’ll see airports shrink back, shrink down, return to being more oriented to providing the technical service rather than the travel experience.”

The appeal of air travel, generally, according to Alegi, is efficiency, so airlines tend to emphasize how efficient their services are.

Direct flights were once the fastest way between two points, even if they made multiple stops. The terminology stuck, even as nonstop flights took over as more time-efficient alternatives. That’s part of the reason this can all be so confusing: Nonstop flights are all direct, but not all direct flights are nonstop. So next time you book a ticket, double-check: is your flight merely direct, or is it nonstop? Otherwise, you may be surprised to find yourself on the ground in some unexpected airport for a few hours

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