What is the FAA's 'NOTAM' system that suffered an outage and caused flight delays?

• The FAA has resumed domestic flights after temporarily pausing them on Wednesday.
• The agency attributed the delays to a problem with its Notice to Air Missions system, or NOTAM.

A critical Federal Aviation Administration system crashed on Tuesday night, leading to thousands of flight disruptions into Wednesday morning.

The system impacted, which temporarily paused all domestic flights, is as called a NOTAM, or a Notice to Air Mission.

The notice reports essential information to pilots when other means of communication cannot be done further in advance. The messages help keep pilots aware of any potential hazards to note in their upcoming flight. These can include things like a runway closure during a specific period of time, or a rocket returning to Earth.

In other words, NOTAMs report a real-time abnormality in the US national airspace system. The messages are different from the FAA's air traffic control system, which is used to separate aircraft. Though, both are safety-critical.

These messages can be as long as 200 pages for long international flights, Reuters reported.

The name was changed in December 2021 from Notice to Airmen to be "inclusive of all aviators and missions," according to the FAA.

By mid-morning on the East Coast, the FAA said flights could resume. "FAA has determined that the safety system affected by the overnight outage is fully restored, and the nationwide ground stop will be lifted effective immediately," Transportation Secretary Pete Buttigieg said in a tweet. "I have directed an after-action process to determine root causes and recommend next steps."

White House Press Secretary Karine Jean-Pierre said in a tweet that there is "no evidence of a cyberattack at this point," but President Joe Biden has "directed DOT to conduct a full investigation into the causes."

In a statement to Insider, United Airlines said customers "may continue to see some delays and cancellations as we work to restore our schedule," and noted it is offering refunds to passengers who no longer wish to travel, as well as waivers for flight changes.

According to FlightAware, over 6,400 flights within, into, or out of the US have been delayed as of 11:00 a.m. on Wednesday, and another 1,000 have been canceled.