What to know about the rare nationwide ground stop issued by the FAA

The US Federal ⁠Aviation Administration said in a statement that the nationwide halt to departures and delays to landings at all US airports that began at about 4pm ET on Friday was caused by “a temporary telecommunications outage”.“Every flight has been accounted for and international flights will be handled on a case by case basis,” the FAA added.Here is what we know about the rare nationwide ground stop issued by the FAA.1. What caused this and how long will it last?It remains unclear what caused the outage, but according to Markwayne Mullin, the former Oklahoma senator now leading the Department of Homeland Security, “there is no indication … that this was a nefarious attack.” There is, as of now, no sign that the “telecommunications outage” that led to the sudden halt to all departures at US airports has been fixed and there is no clear indication of how long the stoppage will last.2. Will flights already in the air be allowed to land?Mullin said in a news conference outside the White House that the immediate priority is restoring communications so that all planes in the could land safely.3. How many flights have been affected?There have been 10,543 flight delays within, into, or out of the US so far, according to the website FlightAware, and 3,580 cancellations.4. What is a ground stop?A ground-stop order by the FAA requires that aircraft remain on the ground and bars them from taking off. Planes already in the air are usually allowed to remain in the air. The FAA has more than 14,000 air traffic controllers who handle the more than 44,000 flights that take off from airports across the US each day, according to FAA data.5. Has this happened before?This is just the second nationwide ​ground stop of all departures since the 9/11 attacks. The previous one came in January 2023, when the FAA paused all ⁠domestic departures for less than two hours.