Airlines aren’t exactly known for handing out freedom. Picking a seat often costs extra, and sometimes so does your carry-on.

In airline speak, “freedoms” are just permissions. And the fifth one is the most useful for anyone chasing a first class experience on a coach budget. You’d never spot it scrolling fares on a packed 6 train, but it’s there.

Countries decide which foreign airlines can land on their turf and sell tickets there.

The fifth freedom lets an airline fly between two countries that aren’t its home, as long as the trip starts or ends back home. Singapore Airlines, for example, flies from Singapore to New York with a stop in Frankfurt. It’s allowed to sell you a ticket for just the Frankfurt to New York part.

Think of it like a train making a few stops on a long trip. You can hop on for just the stretch you need instead of riding the whole line.

Sometimes the plane can’t make a super long trip in one shot, so it’s stopping anyway and might as well sell those seats. Other times, a busy city in the middle simply gives the airline more people to sell to. Airlines love a side hustle as much as your coworker who sells homemade candles at the Union Square holiday market.

Not every government signs off, though, which is why these routes come and go.

An airline flying between two other countries isn’t the hometown favorite with corporate contracts and loyal locals. So it often has to compete harder, which can mean lower fares or more award seats (flights you book with points or miles) than the local airlines offer.

These flights are also usually one leg of a long-haul trip, so you may get a big-plane cabin on a shorter ride. Whether you’ve been eyeing a fancy airline for years or just want to see what the fuss is about, it’s a lower-stakes way to try one without committing to 14 hours.

This isn’t every option, and routes can change, but here are a few fifth freedom routes worth knowing:

It’s not just a U.S. thing, either. For example, Air China flies between Copenhagen and Iceland, a very unexpected way to get to Reykjavik. SWISS does the same between São Paulo and Buenos Aires.

There’s no “fifth freedom” filter on booking sites, so the clue is the airline. If an airline pops up on a route nowhere near its home base, that’s your sign.

If you’re paying with cash, filter by airline on Google Flights and compare it against the usual suspects. If you’re using points, you can often book through the airline’s own program or a partner in its alliance, AKA a group of airlines that let you book each other’s seats with miles. When moving points from a travel credit card over to book, confirm the award seat is there first, since point transfers usually can’t be undone.

Run the math both ways. A fifth freedom flight isn’t automatically cheaper, and a cheap cash fare may not be worth a big chunk of points. If you’d rather someone else do the digging, a deal-alert service like Thrifty Traveler Premium can flag cheap fares and award seats as they pop up. (Use code DEPARTUREDIGEST for $20 off your first year!)

If one of these routes matches your trip, it’s worth a look, whether you’re planning your first big trip abroad or you’re just bored of flying the same U.S. airlines.

You don’t need to plan a trip around one. But if a fifth freedom flight has the better price or the nicer seat, it’s a no-brainer.