USA: US Federal Aviation Administration stops air traffic throughout the country

The FAA halted air traffic across the United States on Friday evening. Flights will not be permitted to take off until further notice. Incoming international flights are assessed on a case-by-case basis. The authorities cited exceptional circumstances and security reasons as reasons. No further details were initially given.

• ?What specific exceptional circumstances and security reasons are there?
• ?How long will the flight stop last?
• ?What impact does the stop have on international air traffic?