The U.S. aviation sector was struggling to return to normal on Wednesday following a nationwide ground stop imposed by the Federal Aviation Administration (FAA) over a computer issue that forced a 90-minute halt to all U.S. departing flights.

Almost 9,600 flights have been delayed so far and over 1,300 canceled, according to FlightAware, in the first national grounding of flights in about two decades. Many industry officials compared the grounding to what occurred after the terrorist attacks on Sept. 11, 2001.

The total number of flights disrupted topped 10,900 and was still rising but airline officials expressed confidence that normal operations could largely return by Thursday.