A sudden FAA system outage grounded thousands of flights nationwide, and it's bad news for travelers but probably not a sign of anything worse.

• Six air traffic control towers, including Boston, went down at the same time, forcing one to switch to an old 1980s backup radio system while repairs are made.
• Nearly 8,000 flights were stuck on the ground or circling, with officials warning full fixes could take until late tonight or even days for the hardest-hit areas.
• Homeland Security said there is no sign of a cyber attack so far, and officials are calling it a telecommunications outage rather than anything more serious.
• The outage hit around the same time as a separate Microsoft cloud service disruption and a National Weather Service radar website outage, fueling speculation about a bigger cause, though none of that has been confirmed.
• Airports are running low on space to park landed planes, and passengers on some flights may be stuck waiting on the tarmac with limited staff to let them off.

Outlook: Officials expect the system to be gradually restored through the day and overnight, with no confirmed link to a cyber attack, though a full return to normal could take time.