Summer Airline Woes Are Here: What to Expect Traveling This Weekend.

A days-long disruption of flights into and out of the Greater New York area is raising concerns about how prepared airlines are for the upcoming 4th of July holiday, a weekend forecast to see record numbers of air travelers.

More than 4 million Americans are estimated to fly this holiday period, according to the AAA, the automobile owners group, an increase of about 11 percent over last year and roughly 6 percent over the record set in 2019. The busiest day for the holiday, with 52,564 flights, will be on Thursday, the Federal Aviation Administration said.

But as travelers prepared for a busy holiday weekend, airlines sought to shift blame to the F.A.A., which runs the country’s air traffic control, for at least some of the thousands of canceled flights and tens of thousands of flight delays nationwide this week.

Here’s what travelers need to know.

What’s the situation at airports in the Northeast?

Travel at New York’s airports, particularly Newark, has been disrupted since the weekend, with many travelers reporting long flight delays and difficulty rebooking canceled flights. In some cases, passengers reported sleeping in airports and waiting in lines or on the phone for hours to reach customer service agents.

One passenger said on Twitter that their connecting flight, operated by United Airlines and departing from Newark Airport over the weekend, had been delayed about 15 hours after being “unboarded” from the plane after midnight. Their family slept on cots in the terminal.

Thunderstorms along the East Coast built up in “the perfect spot” to cut off the busy New York and Florida markets, Chris Citrola, an F.A.A. spokesman, said in a video posted online.

“What happens is a domino effect of issues,” he said. “We have crews that can’t get to where they need to, we can’t get crews out of where they need to go to and that starts turning into a lot of issues at the airport itself.”

What airlines are most affected? Who is to blame?

Of the approximately 4,500 flights canceled nationwide on Monday and Tuesday, more than 30 percent were operated by United, according to FlightAware, a flight tracking firm. Other airlines that reported substantial cancellations included JetBlue Airways, Delta Air Lines subsidiary Endeavor Air and Republic Airways, which flies for Delta, United and American Airlines.

By midafternoon on Wednesday, United, which maintains a hub at Newark Liberty International Airport, had canceled about 15 percent of the nationwide flights it had planned for the day, according to FlightAware. Endeavor had canceled about 12 percent of its flights, while JetBlue had canceled about 9 percent and Republic canceled about 8 percent.

United and JetBlue blamed the problems on the weather, but also on the F.A.A.

In a statement Wednesday, United said that air traffic staffing shortfalls over the weekend contributed to “a tough operating environment.” This blame echoes what its chief executive, Scott Kirby, told staff in a memo earlier this week, saying that “the F.A.A. frankly failed us this weekend.” JetBlue also said in a statement that it had struggled to keep up with its flight schedule after air traffic control limited trips for all airlines into and out of New York airports.

What’s really going on with F.A.A. staffing?

The F.A.A. said it had no air traffic control staffing issues along the East Coast on Monday or Tuesday. In a statement, the agency said that it “will always collaborate with anyone seriously willing to join us to solve a problem.”

Yet air traffic control has long been short-staffed, and controllers at many facilities often work six-day weeks to cover for those shortcomings.

In a report published last week, the Transportation Department found that most of the 26 critical air traffic control facilities it identified were understaffed by 15 percent or more, as of March 2022. One of those facilities, New York Terminal Radar Approach Control, which oversees some of the nation’s most complex and challenging air space, only employed 54 percent of its target number of controllers.

The report stated that the problem has been years in the making, something which United’s Mr. Kirby noted on Monday, too.

“It’s not the fault of the current F.A.A. leadership that they are in this seriously understaffed position — it’s been building up for a long time before they were in charge,” he said in his staff memo.

The F.A.A. has had staffing issues at the top as well. Its last permanent administrator stepped down in March 2022 and the agency is currently being led by its second temporary administrator.

What recourse do passengers with delayed or canceled flights have?

Most U.S. carriers offer compensation to passengers when a flight delay or cancellation is caused by a factor within the airline’s control, such as maintenance problems or short-staffed flight crews. Bad weather and F.A.A. staffing typically do not qualify.

But in cases where the airline is at fault, major carriers will rebook passengers on the same airline at no additional cost, and provide meals or meal vouchers when passengers are left waiting for three hours or more.

To navigate possible disruptions, travelers should download and monitor airline apps, consider purchasing travel insurance — which usually covers flight delays — and switch flights to leave in the morning if possible.

In the event of mass delays or cancellations, there will likely be lengthy hold times for customer service agents. Instead, travelers can phone an airline’s overseas hotline, which will usually see a fraction of the callers, said Scott Keyes, the founder of Going.com, a travel-deals website.

Could this holiday weekend repeat last summer?

“It’s going to be a very hectic weekend and one with potential for disruption,” said Mike Arnot, a spokesman for the aviation analytics firm Cirium, noting that punishing heat in the South and smoky skies from Canadian wildfires could also cause delays.

But Mr. Keyes, of Going.com, said he was feeling optimistic thatthis summer would be better than last year, which he called a “debacle.”

He’s not alone in using that term. From June to August last year, more than 22 percent of all flights were delayed and about 2 percent of flights were canceled, B.T.S. data shows.

To help avoid a repeat and ease pressure on air traffic control, the F.A.A. has relaxed rules at some airports to encourage airlines to operate fewer flights with larger planes. It also opened up 169 new routes to reduce congestion. Airlines hired more staff, opted to use bigger planes and started watching more closely for early signs of problems.

These steps may be working. Of the more than 100,000 flights scheduled for Memorial Day weekend this year, less than 1 percent were canceled, according to FlightAware.