Thousands of air travelers in the United States faced major disruptions on Wednesday after a technical glitch forced United Airlines to ground many of its mainline flights—those operating between major airport hubs. The outage, which lasted more than an hour, triggered a ripple of delays across the airline’s domestic network, particularly at high-traffic airports in Denver, Newark, Houston, and Chicago.

The Federal Aviation Administration (FAA) confirmed it had issued ground stops affecting United flights at these key airports. Although the issue was resolved later in the evening, the FAA cautioned that delays were likely to persist as United worked to clear the backlog.

“We are working with customers to get them to their destinations after a technology disruption on Wednesday evening,” United said in a statement. “The underlying technology issue has been resolved, and, while we expect residual delays, our team is working to restore our normal operations.”

The FAA acknowledged the disruption and said it was in contact with United, offering technical support to expedite recovery. “We’re aware United experienced a technology issue disrupting their operations,” the agency said. “Some delays may continue as they work through the recovery process. We’ve offered full support to help address their flight backlog.”

While the exact nature of the system failure wasn’t disclosed, the situation highlights ongoing vulnerabilities in the nation’s aviation infrastructure. This latest incident follows a string of recent technical disruptions in the U.S. air travel system. In July, Alaska Airlines grounded flights nationwide due to an IT systems failure, while earlier this year, air traffic control issues repeatedly disrupted operations at Newark Liberty International Airport.

The cumulative impact of such glitches is stoking growing concern among passengers about the reliability of air travel in the United States—especially as the post-pandemic travel surge continues to test airline operations and aging infrastructure.

The United incident also comes months after a fatal mid-air collision near Washington’s Reagan National Airport involving a passenger aircraft and a military helicopter, which renewed calls for tighter oversight and modernization of the U.S. airspace system.

As of Wednesday night, United said it was actively rebooking affected passengers and deploying additional support to minimize further disruption. However, many travelers are likely to face continued delays and cancellations into Thursday as the airline works to resume normal operations.