Spirit Airlines could shut down overnight. Here's what travelers need to know

Spirit Airlines could shut down as early as 3 a.m. ET Saturday, according to people familiar with the matter. The carrier has failed to secure a financial lifeline to continue operating, though it hasn't commented on the potential shutdown or its plans.

About 290 Spirit flights are scheduled for Saturday, according to aviation site Flightradar24. Another 381 are scheduled for Sunday.

Travelers with Spirit tickets could be understandably rattled. While there have been some U.S. airlines to shut down in recent years, the budget carrier is larger than most recent airline failures and links major cities like New York, Miami, Detroit and Los Angles — and many others in between — with its Airbus jets.

Here's what travelers need to know:

Immediately? Nothing.

Travelers who are booked on a Spirit flight, like this CNBC reporter is for later this month, are likely to receive a refund if they purchased tickets with a credit card.

If the ticket was bought with a debit card or with loyalty points, however, the chances of recovering funds are slim to none, said Henry Harteveldt, founder of Atmosphere Research Group, a travel consulting firm.

"If you're holding a reservation for a flight on Spirit don't proactively cancel it. Wait for the airline to announce it is shutting down," he said.

Don't count on it.

Spirit has declined to comment on a potential shutdown. If it confirms an end to operations, the carrier will most likely have information on its website about travelers' next steps.

Harteveldt said travelers shouldn't go to the airport expecting to find Spirit staff in the event the airline ceases operations. Call centers are likely to be overwhelmed if they are still staffed.

That could leave passengers with fewer answers than they'd like, but other airlines are likely to help assist affected customers.

Airlines that offer last-minute fares, likely with some discounts, will be available to travelers at airport ticket counters.

United Airlines, JetBlue Airways, Frontier Airlines and American Airlines are among the carriers that have said they are ready to assist Spirit customers and crews if the carrier shuts down.

That could mean scheduling additional flights to carry the stranded passengers, similar to what they do during a hurricane or other natural disaster.

Spirit, known for bright yellow planes, low fares and fees for everything else, had been successful for years, but this week it's been on the brink of liquidation after failing to reach a deal with bondholders for a $500 million government bailout from the Trump administration.

Last year Spirit filed for its second bankruptcy in less than a year, though it's had a host of problems even before then.

A plan to be acquired by JetBlue was blocked. Rising costs upended its business model. An engine defect grounded dozens of its planes. And, more broadly, upscale travel became more popular with consumers, driving airline profits.

At the same time, big, legacy airlines were selling their own basic economy fares that were similar to what Spirit was offering, but with bigger networks.

Airlines have been adding flights since Spirit's bankruptcy filing last year on some of its routes and at major airports. They're likely to keep doing so.

Experts have said they expect fares to rise, at least in some markets, if the discounter goes away, even though the carrier has shrunk substantially.