Now that Spirit Airlines has shut down, its bankruptcy estate is selling off its assets in order to help repay creditors. Those assets include planes, jet fuel, and the right to take off and land at New York’s LaGuardia Airport.Those rights are known as “slots,” and LaGuardia is one of just three slot-controlled airports in the U.S., along with its New York neighbor JFK, and Reagan National in Washington, D.C. Spirit’s slots could fetch upwards of $80 million at auction, because they’re a rare and valuable asset for airlines.A slot is basically the government saying to an airline, “you can take off and land your plane at this super busy airport at this specific time.” They’re essential in busy airspaces like New York’s, said Stephen Abraham, a former air traffic controller at JFK.“Because if they didn't exist, delays would be astronomical,” he said. “Airlines would just oversubscribe, they'd saturate the airspace.”But slots are more than just the right to fly in and out of a busy airport. Samuel Engel, a senior vice president at the consulting firm ICF, said they’re effectively a “limited mini-monopoly.”“It's almost like a taxi medallion or turf assigned to an ice cream truck,” he said. “It says that your airline can fly out of this airport, and other airlines can't.”And that’s valuable. Airlines list slots on their balance sheets. Delta, for example, valued its hundreds of domestic slots at $622 million in an SEC filing last year. Spirit, which had 22 LaGuardia slots, valued those at $83 million.Even if they’re not putting them to use, airlines can make money off slots in other ways.“If an airline is not in a position to take best advantage of that slot in this season or this year, they will lease it to another airline,” Engel said.If an airline needs to borrow money, it can use its slots as collateral. “It's like a house mortgage,” he said. “An airline will borrow against aircraft, it will borrow against spare parts, and it will also borrow against slots.”And, occasionally, an airline will sell its slots as Spirit’s bankruptcy estate hopes to do in an auction next month.“The estate wants to basically raise as much money as they can to pay off creditors,” said Edward Russell, an independent aviation reporter. The catch is that Spirit and the bankruptcy judge won’t ultimately decide who gets the slots. That’s up to the Federal Aviation Administration, and it’s already weighed in.“FAA Administrator Brian Bedford has said he wants another budget airline to get those slots,” Russell said. “So, in other words, a Frontier, an Allegiant, someone along those lines, rather than an American or Delta.”If a budget airline doesn’t win the auction, Bedford has said the FAA could just get rid of the slots. The FAA did not respond to a request for comment.Another regulator is weighing in, too: The Port Authority of New York and New Jersey, which runs LaGuardia. It objected to Spirit’s plan to hold the auction in a court filing, arguing the former airline does not have the right to transfer the slots.But the bankruptcy judge has cleared the way for the auction to move forward.Consultant Samuel Engel expects the slots will eventually change hands. “There's a lot of people making noise right now, but at the end of the day, the dollars are probably going to be what matters.”The right to fly to an airport that’s just a short drive from Manhattan, he said, is just too valuable to take off the table.