Flight delays are easing on a busy travel day. One airline has by far the most cancellations

DALLAS (AP) — Backups are easing at U.S. airports thanks to a break in the weather, but United Airlines continues to struggle, accounting for more than 80% of canceled flights in the United States early Thursday.

United vowed to get back on track for the July 4 holiday weekend when the number of air travelers could set a pandemic-era record, though Thursday is expected to be the busiest day of the holiday stretch at the nation's airports.

Hundreds of thousands of people have had travel plans thrown in the air after a wave of storms raked the Northeast over the past few days and frustrations are running high.

Airports in Chicago, Denver and Newark, New Jersey — all hubs for United — were seeing the most delays on Thursday, according to FlightAware.

By midday on the East Coast, United had canceled more than 390 flights, the bulk of the 475 cancellations toted up by FlightAware. The Chicago carrier is poised to lead all airlines in cancellations for a sixth straight day.

United CEO Scott Kirby blames the airline's struggles in Newark on a shortage of air traffic controllers in the New York City area. Transportation Secretary Pete Buttigieg is pushing back against the criticism while conceding that a key Federal Aviation Administration facility in New York is severely understaffed.

“United Airlines has some internal issues they need to work through. They have really been struggling this week, even relative to other U.S. airlines,” Buttigieg told CNN. “But where we do agree is that there need to be more resources for air traffic control.”

The FAA plans to hire 3,300 controllers over two years, but they won't be ready to help this summer, much less this weekend.

United is offering triple pay to flight attendants who are scheduled off this weekend but agree to pick up extra flights, according to their union. The Association of Flight Attendants also says crews calling in for assignments have been put on hold for three hours or longer.

“We’re beginning to see improvement across our operation,” United said late Wednesday. “As our operation improves in the days ahead, we will be on track to restore our operation for the holiday weekend.”

Scattered showers and thunderstorms may arrive later Thursday in the Northeast, and storms were also forecast farther south along the East Coast through Saturday. The West is under threat of unstable weather for the next several days.

Along with big crowds and storms, a technology issue could add to travelers' difficulties. Federal officials say some airline planes may be unable to fly in bad weather starting Saturday because of possible interference from new 5G wireless service.

American, United, Southwest, Alaska and Frontier say all their planes have been retrofitted with new radio altimeters — those are devices that measure the plane's height above the ground — and they do not expect disruptions due to 5G service.

However, Delta Air Lines has about 190 planes in its fleet of more than 900 that have not been updated because it can't get enough altimeters from its supplier. Delta says it will schedule those planes to avoid landing in poor visibility while it works to upgrade them through the summer.

The issue affects several types of single-aisle planes that Delta uses on routes within the United States, including all its Airbus A220s and most of its Airbus A319 and A320 jets.

Smaller airlines that operate regional flights could also be affected by the radio interference issue, as could flights operated to the United States by foreign carriers.

By midday on the East Coast, about 2,700 flights had been delayed, down sharply from 7,400 on Wednesday.