The FAA's nationwide ground stop on Friday left more than 3,220 flights canceled and roughly 10,200 delayed by 6:40 p.m. ET, according to FlightAware.com — and the two companies most suspected of causing it both say they had nothing to do with it.

Microsoft and Air Space Intelligence, the vendor behind the FAA's new AI-powered SMART air traffic system, issued public denials within hours of the Federal Aviation Administration ordering all planes grounded nationwide because of communications issues.

"We have no indication that the FAA's nationwide ground stop is related to any Microsoft services," Microsoft wrote on X.

Air Space Intelligence went further, explicitly distancing its flagship product from the incident. "The current ground stop is not based on or a result of the SMART system, any product of ASI or our integration with FAA and ATC," the company posted on X.

What happened on Friday?

Thousands of flights were delayed Friday afternoon after the FAA ordered all planes grounded nationwide, citing communications issues. Photos from airports across the country showed crowds forming as passengers were taken off flights and planes lining up on the tarmac.

At a press conference outside the White House on Friday evening, Department of Homeland Security Secretary Markwayne Mullin said authorities were not ruling out any possible cause of the outage. The investigation into the cause is ongoing.

The scale of the disruption is nearly unprecedented. Since federal aviation officials famously froze US airspace during the 9/11 terrorist attacks, only one other nationwide ground stop has occurred.

Why were SMART and Microsoft suspected?

The SMART system, a tool from Air Space Intelligence that uses AI to monitor air traffic and prevent delays, began rolling out to wider use this week — days before the outage. Online speculation quickly pointed to the new system as a possible cause.

That suspicion had a history. In September, POLITICO reported that airline industry veterans were initially nervous about the new system because of the FAA's vague description of it.

Microsoft faced its own questions for a different reason. Earlier in the week, a worldwide Microsoft outage knocked out services like email for hours, snarling the workweek at major companies and inspiring memes from office workers. Some online wondered whether the two events were connected.

The company quickly rejected those claims.

What do the numbers show?

By Friday evening, the toll on US aviation was substantial:

• Over 3,220 flights into, within, or out of the US canceled, according to FlightAware.com
• Roughly 10,200 flights delayed
• One of only two nationwide ground stops since the 9/11 attacks, when federal officials froze US airspace
• One worldwide Microsoft outage earlier in the same week, though the company says it was unconnected

What comes next?

Authorities continue to investigate the cause of the major FAA outage. Neither denial — from Microsoft or Air Space Intelligence — settles the question, and no cause has been identified.

The ground stop was the second of its kind in more than two decades, and no one has yet said what triggered it.