US grounds flights nationwide. What was the reason?

For nearly 4.5 hours, flight departures were halted across the United States. Airport traffic was restored after 8:16 PM Eastern Time.

Known causes

What caused this incident? As reported by Secretary of Transportation Sean Duffy, the cause of the disruption was a failure of an outdated communication system that became overloaded with data during an update. He noted simultaneously that the digital equipment replaced by the administration had recorded no problems. The Secretary of Homeland Security Makwayne Mullin added that the failure occurred during an attempt to patch the system by introducing new hardware, which overloaded the older, analogue one. He ruled out AI in the process.

Mullin stated that there is currently no evidence of a cyberattack or the involvement of third-party states, though he announced that the matter would be thoroughly investigated to rule this out with 100 per cent certainty. He noted that the failure appears „mechanical” and no traces of cyber intrusions were detected. Mullin also emphasised that the matter is unrelated to the Microsoft service outage.

As announced by officials, President Donald Trump is set to declare a state of emergency to expedite the modernisation of the system. Duffy, however, appealed to Congress for additional funding. In his assessment, a total of $50 billion (£40 billion) is needed to build the new system, while Congress has allocated $12.5 billion to date.

Historical ban

According to Fox News, the grounding of flights caused delays for over 8,500 flights and the cancellation of a further 6,500. The result was also mass chaos at airports. Some aircraft were diverted to other airports due to a lack of space. Due to occupied gates, in many instances, passengers were held on board aircraft for several hours.

Friday’s nationwide grounding was only the third such instance in history. Previous occurrences took place after the 11 September attacks and in January 2023 due to a failure of the system of warnings for pilots (NOTAM). In the latter case, the disruption lasted several hours but caused a cascade of flight cancellations and delays for several subsequent days.