WASHINGTON (AP) — American Airlines briefly grounded flights nationwide 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 federal regulators Tuesday. The American groundings couldn’t come at a worse time for the millions of travelers expected to fly over the next 10 days. The Transportation Security Administration expects to screen 40 million passengers over the holidays and through January 2.