FAA halts all departing US flights nationwide in rare safety ground stop

What happened

The Federal Aviation Administration ordered a nationwide ground stop for all departing flights in the United States on Friday afternoon, an action it said was taken "due to extraordinary circumstances and for reasons of safety." According to NBC News, the alert went out at 3:54 p.m. ET with no further explanation, telling airports that departing traffic should stay on the ground until further notice. Inbound international flights would be handled case by case, the agency said.

At the moment the order was issued, 4,042 flights heading for US destinations were already airborne, according to the flight tracking service Flightradar24.

Officials point to a telecommunications outage

Homeland Security Secretary Markwayne Mullin said there was no indication so far of anything nefarious behind the stop, which he attributed "as of now" to a telecommunications outage. He said President Donald Trump had been briefed and that nothing was being ruled out regarding the cause of the communications problem, while insisting that people currently in the air had no reason to worry.

Officials from several agencies involved told NBC News the early stages of the investigation had turned up none of the activity normally associated with a cyberattack, though they cautioned that this assessment could change as investigators learn more. Three senior officials separately said nothing suggested a connection between the incident and the Microsoft outage.

FAA vendor denies its software is involved

Air Space Intelligence, an AI startup working with the FAA on its new SMART air traffic control system, publicly pushed back against speculation about its role. In a statement posted to X, the company said the ground stop was not based on, or a result of, the SMART system, any of its products, or its integration with the FAA and air traffic control.

NBC Chicago reported that shortly before the national alert, both of Chicago's major airports, O'Hare and Midway, had already been placed under ground stops because of an equipment outage.

The safety problem becomes a logistics problem

By 6 p.m., Reagan Washington National Airport was at capacity and Chicago O'Hare was close behind, a source with knowledge of the situation told NBC News, raising the likelihood that incoming aircraft would have to divert elsewhere. Audio captured by LiveATC captured controllers at Newark describing the scene as chaotic, with one saying the airport was running out of space and facing significant gate issues, and another saying he was getting no information from anyone.

Aviation safety expert Jeff Guzzetti told NBC News he considered the outage extraordinary and could not say what caused it. He noted that pilots are trained to operate through communications outages and that information can be relayed through other channels to keep arriving aircraft properly spaced. In his view, the situation was shifting from a safety issue into a large logistics problem, with grounded jets unable to leave and arriving planes potentially forced to park on taxiways.

United Airlines said flights already in the air would continue, but that no new domestic departures would take off while the FAA's order remained in place.

A very rare event

Nationwide ground stops are extremely unusual. The FAA halted all civilian air traffic after the September 11, 2001 attacks, ordering airborne planes to land at the nearest available airport. In January 2023 it grounded flights nationwide again after a failure in the Notice to Air Missions system, which warns pilots of potential hazards.

Why it matters

A single telecommunications failure appears to have frozen the entire US departure system within minutes, with thousands of aircraft aloft and dependent on backup procedures. Even with no early evidence of an attack, the event exposes how much of the aviation network depends on a thin layer of critical infrastructure, echoing the resilience questions raised by the 2023 NOTAM outage. The investigation is at an early stage and NBC News is treating this as a developing story, so the initial read on the cause may yet change.