Flightradar24 says 4,042 flights were airborne and bound for US airports when the FAA's nationwide ground stop was issued at 20:54 UTC, which is 3.54pm ET and 8.54pm UK time. The figure appears on the Flightradar24 live blog.
That is higher than the roughly 3,100 aircraft reported earlier. That number also came from Flightradar24, shared on X by Reuters correspondent David Shepardson, and CBS News, citing the same tracking service, still gives about 3,100 airborne aircraft heading for US airports when the stop began.
The two counts are both attributed to Flightradar24 but differ by more than 900 aircraft, and neither outlet explains the gap. We have not been able to reconcile them, so for now they stand as conflicting figures.
The ground stop itself remains in place. The FAA advisory cites only "extraordinary circumstances" and safety, and says all departing traffic should remain grounded until further notice.