The failure of a system that alerts pilots and other flight personnel about hazards and other key information led to the temporary grounding of all US domestic flights on Wednesday morning.
From about 7am to 9am, the FAA halted all US domestic departures, a disruption that impacted at least 4,000 scheduled flights, in the first nationwide ground stop since September 11, 2001.
The FAA the disruption was caused by an outage in the system that alerts pilots to hazards and changes to airport facilities and procedures that had stopped processing updated information.
‘The FAA is still working to fully restore the Notice to Air Missions (NOTAM) system following an outage. While some functions are beginning to come back on line, National Airspace System operations remain limited,’ the FAA said in a statement.
Travelers wait in the terminal as an Alaska Airlines plane sits at a gate at Los Angeles International Airport in Los Angeles on Wednesday during a nationwide ground stop
Here is so far known about the outage, its origins, and potential impact:
What is the NOTAM system?
The halt on takeoffs was prompted by a failure in what is known as the Notice to Air Missions (NOTAM) system.
A NOTAM is a notice containing information essential to pilots and other flight personnel, but not known far enough in advance to be publicized by other means.
Before commencing a flight, pilots are required to consult NOTAMs, which list potential adverse impacts on flights, from runway construction to the potential for icing.
Information can go up to 200 pages for long-haul international flights and may include items such as runway closures, general bird hazard warnings, or low-altitude construction obstacles.
The NOTAM system is seen above, with a list of advisories for JFK Airport in New York. Advisories issued prior to the disruption still appeared during Wednesday’s outage
The system used to be telephone-based, with pilots calling dedicated flight service stations for the information, but has now moved online.
In an advisory, the FAA said its NOTAM (Notice to Air Missions) system had ‘failed’.
There was no immediate estimate for when it would be back, the website showed, though NOTAMs issued before the outage were still viewable.
The outage caused widespread disruption and led to a nationwide ground stop. All aircraft are required to route through the system, including commercial and military flights.
European flights into the US appeared to be largely unaffected.
Why are all US flights grounded?
With the NOTAM system offline, air traffic controllers can’t risk allowing pilots to take off without potentially key information about hazards on their route.
The FAA ordered all US flights to delay departures until 9am Eastern, though airlines earlier said they were aware of the situation and had already begun grounding flights.
A display shows flights, many delayed, at LaGuardia Airport in New York on Wednesday. A computer outage at the FAA brought flights to a standstill across the U.S.
At 8.40am, there were more than 4,000 delayed flights within, into or out of the United States, according to the flight tracking website FlightAware, exceeding the number of all delayed flights on the previous day.
More than 1,900 flights have been cancelled, and those numbers are likely to grow.
More than 21,000 flights were scheduled to take off in the U.S. today, mostly domestic trips, and about 1,840 international flights expected to fly to the US, according to aviation data firm Cirium.
Could this be a cyberattack?
The White House said that there is no evidence of a cyberattack, but President Joe Biden directed the Department of Transportation to investigate the cause of the disruption.
President Joe Biden addressed the FAA issue Wednesday before leaving the White House. He said he had just been briefed by Transportation Secretary Pete Buttigieg, who told him they still had not identified what went wrong.
Grounded planes at Washington Reagan airport on Wednesday morning after an FAA systems failure grounded all flights across the country
‘I just spoke to Buttigieg. They don´t know what the cause is. But I was on the phone with him about 10 minutes,’ Biden said. ‘I told him to report directly to me when they find out. Air traffic can still land safely, just not take off right now. We don´t know what the cause of it is.’
Buttigieg said in a tweet that he is in touch with the FAA and monitoring the situation.
Has this ever happened before?
The last time a nationwide ground stop was issued, halting all departures from US airports, was in the immediate aftermath of the terrorist attacks on September 11, 2001.
Regional or airport-specific ground stops have been issued since then, primarily over security incidents, though even those are quite rare.
Tampa: Passengers stranded at Tampa airport in Florida on Wednesday
For instance, on January 10, 2022, the FAA issued a ground stop for the West Coast and Hawaii.
Though officials gave no explanation for the halt in takeoffs, it was widely believed to be related to a North Korean missile test.
Experienced pilots call the outage of the NOTAM system unprecedented, and cannot recall a similar incident with such widespread impact on flights.