A number of major airlines in the U.S. and around the globe were grounded completely for several hours because of a major technology outage affecting Windows-based systems, leaving millions of travelers stranded. In the U.S., the FAA said around 1:45 a.m. Eastern Friday that United, American, Delta and Allegiant had all been grounded by the outage, although the airlines began saying Friday morning that service was resuming. Around 5 a.m. Eastern Friday, American Airlines posted to X, formerly Twitter, saying that they had restored service, and thanked customers for their patience. "Earlier this morning, a technical issue with a vendor impacted multiple carriers, including American," the airline's post read. "As of 5:00 a.m. ET, we have been able to safely re-establish our operation. We apologize to our customers for the inconvenience." It's unclear how many American flights were delayed or canceled because of the overnight grounding. Just before 8 a.m. Eastern, Delta posted an update saying it had "resumed some flight departures." "Additional delays and cancelations are expected Friday," Delta said. The airline issued a travel waiver for flights departing on Friday. It urged customers to manage their flights on delta.com or the Fly Delta app. Around 6:30 a.m. Eastern, United Airlines said some flights were resuming and the company said it was offering ways for customers to change their plans to account for the delays caused by the outage. "A third-party outage is impacting computer systems, including at United and many other organizations worldwide," the statement reads. "As we work to fully restore these systems, some flights are resuming. Many customers traveling today may experience delays. We have issued a waiver to make it easier to change your travel plans at United.com or the United app." Travelers at Los Angeles International Airport slept on a jetway floor, using backpacks and other luggage for pillows, due to a delayed United flight to Dulles International Airport early on Friday. READ MORE: https://www.9news.com/article/news/nation-world/airlines-grounded-by-technology-outage/507-237a74be-322a-4e5e-8baa-d37dba0ad83b More local videos here: https://youtube.com/@9news Subscribe to NEXT: https://youtube.com/@Nexton9NEWS Stay connected: 9NEWS Website: https://www.9news.com/ Facebook: https://www.facebook.com/ilike9news Twitter: https://twitter.com/9NEWS Instagram: https://www.instagram.com/9newsdenver/ Download the 9NEWS App: https://www.9news.com/appredirect/ Sign up for the 9NEWSLETTER: https://www.9news.com/email 9NEWS (KUSA) is located in Denver, Colorado.