A corrupt computer database file has been initially blamed for a “major” Federal Aviation Administration IT failure that grounded thousands of domestic flights across the United States on Wednesday morning.

The catastrophe arose because the Notice to Air Missions (NOTAM) system, which keeps pilots and other airport staff updated with real-time information about aviation hazards and airport facilities across American airspace, reportedly stopped processing data.

“Our preliminary work has traced the outage to a damaged database file. At this time, there is no evidence of a cyberattack,” the FAA said.

“The FAA is working diligently to further pinpoint the causes of this issue and take all needed steps to prevent this kind of disruption from happening again.”

The FAA is trying to find out if any one person or “routine entry” into the database was responsible for the corrupted file, an official familiar with the investigation told CNN.

The same file corrupted both the main system and its backup, people familiar with the review, who asked not to be identified, told Reuters.

More than 11,300 flights were delayed or cancelled on Wednesday in the first national grounding of domestic flights in almost 20 years, according to the news organisation.

The system is used to notify both pilots and airport and ground staff of incidents that may affect take-offs, landings and routes, including: air shows and parachute jumps, military exercises affecting airspace, volcanic ash clouds, obstacles close to airfields, significant flocks of birds likely to cause bird strikes or closed runways and taxiways.

“NOTAMs are essential for the safe continuation of global air travel,” aviation analyst Alex Macheras told The Independent.

“These essential notices and directives ultimately keep the world’s aviation sector, specifically flight crew and all personnel concerned with flight operations, informed and up to speed with latest air travel-related directives, operational updates, security, weather and warnings.

“With a system failure affecting NOTAMs, operations will be disrupted almost immediately and this will soon be felt elsewhere across the world, including for flights waiting to depart to the US.”

Unable to guarantee passenger safety without vital information available, the FAA had no choice but to order airlines to pause all domestic departures until 9am EST [2pm GMT] on Wednesday “to allow the agency to validate the integrity of flight and safety information”.

Flights already airborne were allowed to continue their journeys and land as normal, however.

The disaster left travellers stranded in airport departure lounges across the country – many tweeting away their frustration – with schedules in chaos, thousands of planes grounded on the tarmac and no word on when the system would be back up and running as engineers scrambled to fix the problem.

US president Joe Biden and his transport secretary Pete Buttigieg assured the public that the FAA was doing all it could to restore NOTAM and White House press secretary Karine Jean-Pierre moved to dismiss speculation by stating that there was “no evidence of a cyberattack” being responsible for the disaster and that the Department of Transportation (DoT) would be conducting “a full investigation into the the causes”.

The FAA subsequently announced that the problem had been resolved and that flights would be able to continue, with airports gradually resuming departures but facing a nightmarish backlog as a result of the outage.

“Normal air traffic operations are resuming gradually across the United States following an overnight outage to the FAA’s Notice to Air Missions system that provides safety information to flight crews,” it said in a tweet.

“The agency continues to look into the cause of the initial problem.”

Mr Buttigieg reiterated the DoT’s intention to find out precisely what had caused the chaos, tweeting: “I have directed an after-action process to determine root causes and recommend next steps.”

As planes returned to the skies, NBC News reported that the FBI had likewise seen no evidence that hackers were to blame for the crisis, citing a senior law enforcement official, as well as security experts who believed “a bad software update” was the more likely cause.

Until the internal investigations are completed, we will not know for sure precisely what caused the NOTAM malfunction.

However, air industry insiders were quick to suggest on social media that the system in question is vulnerable to overzealous use, with users allegedly too often prone to uploading needless posts, which can leave flight planners swamped and forced to sort through multiple pages when they have limited time at their disposal, causing them to, potentially, miss out on key information relevant to their journey.

Speaking on BBC News, business correspondent Victoria Valentine underlined the scale of the problem by pointing out that the NOTAM system can include up to 200 pages of information for a single long-haul flight, which, given that there were 21,464 flights scheduled to take off from 19,000 airports across the US on Wednesday, amounts to an awful lot of data.

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