American Airlines briefly grounded flights nationwide Tuesday due to a technical issue just as the Christmas travel season kicks into overdrive and winter weather is threatening more potential problems for those planning to fly or drive. American flights were cleared to fly by federal regulators about one hour after a national ground stop order was issued by the Federal Aviation Administration. There were 1,447 delays for flights entering or leaving the U.S. early in the day, with 28 cancellations. Snow was falling early in New York and Dallas-Fort Worth International, which is American Airlines' main hub, was getting hit with rain.