Major U.S. airlines, including Delta Air Lines and United Airlines, are gradually restoring operations after a significant IT vendor-related technical issue forced multiple carriers to ground their flights on Friday.

Despite efforts to resume services, delays and cancellations are expected to continue as airlines work to recover from the disruption that impacted thousands of passengers.

According to FlightAware, as of 1:23 pm ET on Friday, over 2,200 flights had been cancelled across the United States, with nearly 7,000 more delayed. Delta and United Airlines announced the resumption of some flights but anticipated ongoing delays and further cancellations. Both airlines issued travel waivers to accommodate affected passengers.

The technical issue disrupted various systems, including those used for calculating aircraft weight, customer check-ins, and call centre operations, according to a statement from United Airlines. American Airlines, which had previously issued a ground stop notice, confirmed it had safely resumed operations. Southwest Airlines reported it was not affected by the outage.

The outage also impacted other sectors globally, including banking and healthcare, due to issues at Microsoft and cybersecurity firm CrowdStrike. Frontier Airlines attributed its operational disruptions to a “major Microsoft technical outage.” CrowdStrike’s CEO, George Kurtz, stated the problem originated from a defect in a content update for Microsoft Windows hosts.

The U.S. Federal Aviation Administration (FAA) reported it was closely monitoring the situation and had received requests for assistance with ground stops from several airlines. Parcel delivery companies such as FedEx and United Parcel Service (UPS) also reported substantial disruptions and potential delivery delays due to the technical issue.

Microsoft indicated that the outage began around 6 pm ET on Thursday, affecting a subset of customers using multiple Azure services in the Central U.S. region. Azure is Microsoft’s cloud computing platform that supports building, deploying, and managing applications and services.

As the affected airlines and other businesses work to restore normal operations, this incident highlights the critical need for robust IT systems and contingency plans to mitigate the impact of such widespread disruptions.