EXPLAINED | Why the FAA Ordered the Biggest US Ground Stop Since 9/11

On Friday, 13 November, the US Federal Aviation Administration (FAA) ordered a nationwide ground stop after air traffic controllers began getting inconsistent radar and communications data. About 3,500 aircraft were already airborne, US Transportation Secretary Sean Duffy said. Departures could start again shortly after 8 p.m. Eastern time, more than four hours after the order. By then, the routes those planes and crews were meant to fly next had already been disrupted.

What did controllers do with 3,500 planes already in the air?

They kept handling the flights already aloft while the FAA stopped adding most new departures. The agency said it had accounted for every flight and was managing inbound international flights case by case. Some aircraft landed as planned. Others went back to where they took off or landed at another airport. By 7:05 p.m. Eastern, aviation data firm Cirium counted 827 diversions. Of those, 670 were returns to the departure airport and 157 were landings elsewhere.

By the time Duffy briefed reporters, he said his latest count showed fewer than 400 aircraft still in US airspace. He said the FAA allowed critical flights, including medical evacuations and flights carrying life-saving medicines, to continue.

What is an FAA ground stop?

It’s an order to hold affected flights before takeoff. The FAA uses ground stops when airports or the air traffic control system can temporarily handle fewer aircraft. Most are narrower, affecting flights headed to a particular airport or area. This one covered airports nationwide. Think of a plane waiting at its gate in Los Angeles. Holding it there gives controllers room to deal with aircraft already approaching crowded airports or being sent to alternate ones.

What failed at 3:36 p.m.?

Duffy said controllers began seeing instability at 3:36 p.m. Eastern on Friday, or 2:06 a.m. IST on Saturday. The trouble affected regional centres that guide aircraft between airports and approach control facilities that sequence planes arriving and departing around airports. The FAA advisory put the start of the nationwide stop at 3:53 p.m. Eastern.

Radar helps controllers see where aircraft are. Radio lets them tell pilots where to go. Both depend on ground networks getting information to the people who need it. Duffy said older networking equipment became overloaded and delivered inconsistent data. Some radar and communications stayed available, which let controllers guide aircraft down. He said newer switches that move data using internet protocols kept working. Those protocols can run over dedicated networks. They are also used on the public internet.

Was it a cyberattack, and did Microsoft have anything to do with it?

Officials said their initial checks found no evidence of a cyberattack. Homeland Security Secretary Markwayne Mullin said there was no indication of a link to the separate Microsoft outage. Microsoft also said it saw no indication of a connection. Mullin said new equipment had overwhelmed older systems. Duffy described what the overloaded equipment did. The exact trigger and how the trouble spread across centres remained under investigation.

Why did the cancellations continue after the FAA reopened?

Restarting departures cleared aircraft to fly as capacity allowed. A diverted plane could still be hundreds of kilometres from its next passengers. The crew might be somewhere else or approaching its legal duty limit. An arriving flight could also have to wait for a gate occupied by a plane that had never left. Each problem can knock out another flight later in the day.

Duffy put the restart at 8:15 p.m. Eastern, or 6:45 a.m. IST on Saturday. In its updated coverage, Reuters cited Flightradar24’s Friday tally of more than 6,600 cancellations and 8,600 delays. That is a count of flight disruptions. Cirium’s diversion tally measures where aircraft that took off ended up.

Has the US ever done this before?

Yes. In January 2023, the FAA paused US domestic departures for about 90 minutes after the system that distributes safety notices to pilots failed. The agency’s preliminary review traced that failure to files contractors accidentally deleted while working on the live and backup databases. Friday’s failure reached the radar and communications systems controllers use to manage air traffic.

A closer technical comparison came at Newark in April 2025. The FAA said a telecommunications breakdown interrupted communications and radar displays serving that airport. It subsequently announced steps to replace connections with fibre and add redundancy, meaning extra paths the data can take if one fails. Newark showed how a communications fault could affect one airport. Friday showed how widely the disruption could spread.

What does it mean for Air India passengers?

Air India warned of possible disruptions to flights in both directions and advised passengers to check their flight status before leaving for the airport. A US departure can be held or cancelled directly. A later flight from India can also be delayed if the aircraft or crew meant to operate it is still out of position. The airline’s warning gave no route-by-route tally.

Under US rules, if an airline cancels a flight to or from the US and you choose to abandon the trip, you’re entitled to a refund. The rule also covers significant schedule changes, including an international flight scheduled to arrive at least six hours late.

India has had its own reminder of how much rides on information reaching a controller on time. In November 2025, delays in processing flight-plan and clearance messages disrupted operations at Delhi airport. India’s civil aviation ministry told Parliament that the Airports Authority of India restored the system on 8 November and replaced core switches and database servers. That incident involved flight messages at one airport.

Can the FAA replace its oldest equipment while keeping flights moving?

That is the test now. Congress allocated $12.5 billion in 2025 to start the overhaul. The first phase includes replacing old communications links with fibre and is targeted for December 2028. In September, the Government Accountability Office, Congress’s watchdog, said the FAA still lacked a single schedule tying thousands of installation projects together. That matters when several installations are planned at the same site while controllers still have to run it.

Before Friday’s outage, the administration had asked Congress for $30.1 billion for airport and air traffic upgrades. The immediate question for investigators is which equipment first became overloaded and why other parts of the network felt it. That finding should help the FAA decide which links to replace first and which backups need to work independently.