Update: At 2:22 PM Eastern, an American Airlines spokesperson told Ars that the company has "resolved connectivity issues that led to a ground stop today at our Chicago, Dallas/Fort Worth and Miami hubs. We apologize for the inconvenience and are working to get our customers on their way as soon as possible."

Earlier today, a network outage at Chicago's O'Hare International grounded many American Airlines flights today. As the company tried to restore service this afternoon, flights from those three major hubs were halted. American has not said which systems were affected by the outage, or what caused the network connectivity issue.

The Federal Aviation Administration announced via Twitter at 1:33 PM Eastern that American had requested a ground stop for flights out of the three airports:

FAA Air Traffic Alert: @AmericanAir requested a ground stop for all of their traffic in and out of DFW/ORD/MIA due to their computer issue. — The FAA (@FAANews) September 17, 2015

During the issue, American's Twitter feed was filling up with responses to customers: "We’re working to resolve technical issues and apologize for the inconvenience." Some of the complaints had nothing to do specifically with the grounded flights, however—it appears the outage has also affected parts of American's website, blocking access to frequent flyer accounts and other customer data. That suggested a broader issue within American's corporate network.

The outage parallels similar problems at United Airlines in July, when United's systems also suffered a "network connectivity issue." United's outage, however, was more severe, and affected over 4,900 flights worldwide. United's problems were caused by problem with a single network router.

Both United and American have gone through recent mergers—American just completed its merger with U.S. Airways, which will make its final flight under that name next month. The merger has been plagued with system integration concerns, including problems integrating the ticketing systems. In March, the Washington Post reported on problems with the integration of customer data, including the experience of one American customer who, when trying to change her name on a ticket after getting married, was told that the airline lost her booking. Viviane Tran told the Post, “I waited for at least 15 minutes; when she finally came back she told me that we’ve lost our seats and she’s unable to re-book us on the same flights because she does not have access to American Airlines’ inventory."