The United States on Friday lifted an hours-long ground stop at the nation's airports, with top officials explaining that the disruption was due to old equipment and not a cyberattack or sweeping Microsoft outage. Transportation Secretary Sean Duffy told a late-night briefing at the White House that US airspace was now "opened up," while warning it would take time for the travel chaos to clear. "At 8:15 tonight Eastern Time, we've opened up the airspace," Duffy said. "Now…