United Airlines' computer systems went down Wednesday morning -- across the U.S. -- causing a travel nightmare domino effect around the world.
Systems slowly came back online near 10 a.m., when passengers started boarding some jets.
"We experienced a network connectivity issue. We are working to resolve and apologize for any inconvenience," the jetliner giant tweeted.
An FAA formal order halting all new take offs went into effect at 8:26 a.m.; it was lifted at 9:47 a.m.
Agents were unable to check in passengers and boarding pass kiosks went down.
At one point, agents even start hand-writing tickets.
The repercussions will last days because of how jammed flights are, all the missed connections and other issues, experts say. In all, about 100 flights were grounded; the number may not seem small but the ripple effects are much greater.