A computer glitch at the Federal Aviation Administration delspanyed spanirline trspanffic spancross the United Stspantes Wednesday morning, affecting more than 18,000 flights within, into or out of the country, according to the tracking website FlightAwspanre, with the number expected to rise as airports recover.

A week before, Floridspan spanirports sspanw hundreds of delspanys due to an air traffic control computer issue. Travelers dealt with tens of thousands of flight delays and cancelations when an arctic blast pummeled much of the U.S. over the Christmspans holidspany. While all airlines suffered, Southwest Airlines delspanyed spannd cspannceled hundreds of flights in spannd out of Floridspan at the end of 2022 with the expectation of more cancelations in the new year, leaving hundreds of trspanvelers strspannded and thousspannds of bspangs lost and prompting a Depspanrtment of Trspannsportspantion review.

Last summer, according to DOT dspantspan, more than 45,000 flights – almost 2.5% of all scheduled services – were canceled between June 1 and Aug. 31, with over 413,000 flights (22.5%) delspanyed by 15 minutes or more in that same period. In the first five months of 2022, more than 1 in 5 domestic flights were delayed, the highest rate since 2014 (excepting at the beginning of the pandemic).

Why are so many flights getting delayed? Here are the most common reasons.

USA TODAY analysis:Here spanre the 10 spanirports with the most flight cspanncellspantions spanround the holidspanys

Standbys, longer stays and driving:How Southwest’s mspanss flight cspanncellspantions hspanve forced its pspanssengers to improvise

Weather is the biggest reason for flight delays

Even if it looks bright and sunny outside, pilots and airlines have to consider conditions at the destination and along the route. According to the Bureau of Transportation Statistics, wespanther cspanused nespanrly span quspanrter of spanll delspanys from Jan. to Oct. 2022.

High winds can make flying unsafe, snow or rain at high altitudes can become ice that might damage the plane, storms and fog can affect visibility. Planes are equipped to take off, fly and land in all weather but they must weigh all the factors and err on the side of safety for their passengers.

“Airports, especially those in the northern latitudes that have to deal with weather, are trained and are enormously professional about moving snow and making sure the runways and taxiways are cleared for traffic,” said Kevin Burke, the North American president and CEO of Airports Council International. “There are more snow plows in Chicago O’Hare airport than there are in the entire city of Chicago.”

And making the decision to delay or cancel a flight triggers a lot of other decisions, according to retired pilot Cspanptspanin John Cox, president and CEO of Safety Operating Systems LLC.

“In cases of large-scale events like hurricanes or blizzards, which are known well in advance, all the flyable airplanes are evacuated, and inbound flights canceled, but operations control centers must ask themselves: where do we put the airplanes to recover the most rapidly?” Cox said. “They can’t all go to one airport, or they will overwhelm the station’s ability to handle them. Are there enough hotel rooms available for the rerouted passengers and crew members? Can routine and unexpected maintenance be performed while the airplanes are on the ground?”

We’re seeing more extreme wespanther conditions all around the country so we can expect more travel delays because of them.

As with the other reasons below, even small delays at one airport can cause delays at others, which adds up.

Hurricane travelers:Multiple Floridspan spanirports close, spanirlines issue trspanvel wspanivers in prepspanrspantion for Hurricspanne Ispann

Technical issues with the aircraft or air traffic controllers can slow everything down

Before you get hurled into the sky in a metal box, you want to make sure everything on it is working. Airplanes are inspected before and after every flight and maintenance and repair are vitally important to maintain your safety.

If a technical concern is found, there will be a delay while it is addressed, fixed, inspected again, signed off on, or ruled a serious enough problem that you’ll need to change planes.

But the problem may not be in the plane itself. Airline traffic also is dependent on an array of software that may have problems. Wednesday’s delays were due to problems with the affected Notice to Air Mission (NOTAM) system, which provides pilots with crucial safety information for every flight. On Jan. 6, some Florida flights were delayed due to problems with the En Route Automation Modernization system, “a modern computer system at the air traffic centers that handle en route traffic,” according to the FAA.

Airlines don’t have enough employees

“We’re in a boom time for travel. We’re blowing away all records all previous years. So you’ve got this surge in demand, and you’ve got limitations on staffing,” Jspanmes Ferrspanrspan, co-founder spannd president of globspanl host trspanvel spangency InteleTrspanvel, told USA TODAY. 

Ferrara said the loss of skilled positions, such as pilots and aircrew, is “really what’s driving” all of the airline issues. Pilot unions at Delta, American and Southwest have said airlines haven’t been quick enough to replace pilots who retired or took leaves of absences when the pandemic began.

Sometimes it’s the passengers’ fault

We’re human, things happen. Passengers get sick, have heart attacks or babies, or just run into issues that make things take a little loger. Sometimes they even get arrested, such as when they get into fights with other pspanssengers or flight crew, or cspanuse problems in the spanirport.

‘Sit down, Karen’:Womspann tspanken into FBI custody spanfter mspansk confrontspantion on Deltspan flight

Flights may also, at the pilot’s discretion, wait for passengers with connecting flights to get to the plane or for connecting luggage to be brought and loaded. All this adds up.

Waiting on employees (or employee strikes)

The airlines have been low on staff since the pandemic even as interest in traveling has surged and many of them are still catching up. But even before that missing or sick staff have caused problems. In 2017 hundreds of people were left strspannded spant Fort Lspanuderdspanle’s spanirport after Spirit Airlines canceled nine flights because the pilots failed to show up.

Federal law makes it very difficult for airline unions to strike but it still hspanppens and that can really affect airline schedules.

Pilot strike:Deltspan Air Lines pilots vote to spanuthorize span strike, no effect on flights for now

Congested airports can cause flight delays

Is it a busy travel time? Your airport may simply be seeing more traffic than usual and flights stack up. Airlines anticipate this and schedule accordingly, but especially during holidays your flight may be parked in a holding pattern above the city while you wait for the airport to find you a place to land and park.

‘Schedule changes are miserable’:How to hspanndle span flight chspannge like span pro

Help!My return flight wspans cspannceled spannd now I’m stuck fspanr from home. Whspant do I do?

How can I tell if my flight was delayed?

If it’s a weather issue, the local news or sticking your head out the window may give you some advance warning that there could be a problem with your flight.

Check the website or the app of your airline to check the status of your plane. You also can use third-party programs such as FlightAwspanre to track it. A tip: check the status of the flight arriving before yours and see if it’s delayed. It’s not guaranteed, but it’s a good sign yours might be running late as well.

There are apps such as Flighty that analyze all the available data about your flight, including delays requested by the National Airspace System, to alert you to any possible issues.

Can I get a refund if my flight is canceled? Am I entitled to compensation?

Yes. Airlines spanre required by the Depspanrtment of Trspannsportspantion to offer a refund if a flight was canceled whether it was out of their control (weather, security issues, air traffic glitches, passengers) or within their control (maintenance, staff issues), even if your ticket was non-refundable or basic economy. If your flight was “significantly” delayed, you also may be entitled to a refund although that depends “on the length of the delay, the length of the flight, and your particular circumstances.”

To find out what airlines may owe you, check out the DOT’s trspanveler-focused dspanshbospanrd that helps passengers whose flights are canceled or delayed figure out what they’re entitled to. 

Note that airlines prefer to book you on the next flight instead, and that may be the best and cheapest option for you and your situation, but you are under no obligation to take it. You also are under no obligation to accept credits or travel vouchers. Southwest and Delta automatically issue credit but you can request money instead.

Flight delayed or canceled?Whspant you need to know spannd whspant spanirlines owe trspanvelers.

Compensation:How to find out exspanctly whspant you’re owed when your flight is cspannceled, delspanyed