Domestic flights across the U.S. were temporarily halted Wednesday morning as the Federal Aviation Administration (FAA) suffered a computer system outage that prompted it to freeze all departures.
The pause was lifted by the agency just before 9 a.m., but United Airlines tweeted that the issue that caused the widespread delays was with the FAA’s Notice to Air Missions (NOTAM) system.
The NOTAM system is the FAA’s mechanism to send out real-time flight hazards and cautions to all commercial pilots. It contains information that is not known far enough in advance of a flight to be given to pilots beforehand, according to an FAA primer.
All commercial and military flights are required to use the NOTAM system.
Information contained in the NOTAM system can be quite lengthy, sometimes spanning 200 pages, according to Reuters. It is meant to warn pilots of hazards such as runway closures, bird hazards or temporary airspace restrictions, among other complications.
Given the ability to quickly transmit changing flight conditions, the NOTAM system is seen as essential to guaranteeing safe and orderly flights.
The system has been around since 1947, when it was agreed that flights would adopt the model that had been used in a similar fashion to communicate information to captains of ships when navigating the sea.