“Sep 13, 2001: DOT [Department of Transportation] ordered the reopening of the national airspace to U.S. air carriers, effective 11:00 a.m., provided that the airport involved had implemented the new security measures. …Foreign air carriers were still not allowed to fly into the United States, with certain exceptions, but could depart if they met the new security standards. General aviation remained grounded, except in Alaska.”
– FAA, “Chronology of the September 11 Attacks and Subsequent Events Through October 24, 2001,” FAA Believed Second 9/11 Plane Heading Towards NY for Emergency Landing, The National Security Archive, Sep. 9, 2005