The Federal Aviation Administration has grounded all flights in the US until further notice, and it has not said why.
The order came suddenly on Friday. The only detail available so far is a missing one: no reason was immediately given for the grounding. The order also has no stated end point, since it runs until further notice.
That leaves two open questions. The first is cause, and nothing in the available information answers it, so any theory would be a guess. The second is duration. An order with no clock attached gives airlines, airports and passengers nothing to plan around.
What the order does establish is scope. It covers every flight in the US, not one region or one carrier. That makes the agency's silence the story for now, and it makes the FAA's next statement the one that matters. Until it arrives, travelers are best served by checking their own airline's status page rather than relying on secondhand explanations.