United Airlines briefly halted all mainline departures across the United States on Wednesday evening after a technology outage struck the system that calculates aircraft weight and balance, prompting the carrier to ask the Federal Aviation Administration for nationwide ground stops. The FAA listed ground stops at United’s key hubs, including Newark, Chicago O’Hare, Denver, Houston and San Francisco, starting about 8 p.m. Eastern Time. By 9:25 p.m., flight-tracking service FlightAware reported 870 United flights—roughly 28% of the airline’s daily schedule—were delayed. United said the problem was fixed and flights began departing again at around 9:19 p.m. ET, but cautioned travellers to expect residual delays while it works through the backlog. “Safety is our top priority,” the company said, apologising for the disruption. The incident adds to a series of technology-related breakdowns at U.S. carriers this year, including Alaska Airlines’ fleet-wide grounding in July. The glitches have intensified scrutiny of airlines’ IT infrastructure as passenger volumes approach record highs.