All United Continental flights in the U.S. were grounded Wednesday due to computer problems.
Just shy of two hours after the problems began, the Federal Aviation Administration lifted the ground stop order.
United said it was recovering from a "network connectivity issue" and restoring regular flight operations. The airline said that it would have a waiver available on its website for customers that are able to change their flight plans.
It is the second time in two months that the carrier has been hit by major technical issues.
The Chicago company had halted all takeoffs in the U.S. on June 2 due to what the airline described as computer automation issues.
The Federal Aviation Administration used the same language in its notice about the outage Wednesday.
United suffered a series of computer problems in 2012 after switching to a passenger information computer system previously used by merger partner Continental Airlines.
In each case, hundreds of flights were delayed. A number of high-paying business travelers defected to other airlines and revenue dropped.
"We don't know everything behind this morning's issues yet, but today's incident underscores the sense that something is very wrong at United," said Gary Leff, co-founder of frequent-flier website MilePoint.
Shares of United Continental Holdings Inc. slid 2 percent to $53.20 in morning trading.
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