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What is NOTAM, the FAA’s system that failed and caused mass delays?

A traveler looks at a flight board with delays and cancellations at Reagan National Airport in Arlington, Va., on Wednesday. (Patrick Semansky/AP)

As the Federal Aviation Administration directed U.S. airlines to temporarily halt all domestic departures Wednesday, passengers booked on nearly 4,600 delayed flights waited for an outage to be fixed in a system that many travelers might have been learning about for the first time.

The FAA announced about 6:30 a.m. Eastern time that its Notice to Air Missions system, or NOTAMs, had failed, affecting operations “across the National Airspace System.” In another update, the FAA noted that it had “ordered airlines to pause all domestic departures until at least 9 a.m. Eastern time to allow the agency to validate the integrity of flight and safety information.”

“The FAA is still working to fully restore the Notice to Air Missions system following an outage,” the agency wrote on Twitter.

Just before 9 a.m. Eastern time, the FAA said that “normal air traffic operations are resuming gradually across the U.S.” after an overnight outage of its NOTAM system.

“The ground stop has been lifted,” the FAA wrote. “We continue to look into the cause of the initial problem.”

The outage in the system, which issues essential notices to flight personnel, has caused mass delays across the United States. Nearly 4,600 flights within, into or out of the United States were delayed as of 9:30 a.m. Eastern time Wednesday, according to the flight tracking website FlightAware. At least 832 flights have been canceled.

FAA systems restored after nationwide outage, ground stop

The FAA emphasized that “all flights currently in the sky are safe to land” and that departures are resuming at major hubs, such as Newark Liberty International Airport and Hartsfield-Jackson Atlanta International Airport.

What is a NOTAM?

A NOTAM is a notice to personnel containing important safety information including potential facility outages and hazards that could affect flights. The information in a NOTAM is unclassified and is not known far enough in advance to be publicized any other way, according to a 2021 PowerPoint presentation from the FAA on the history of NOTAMs.

The construction of a NOTAM includes a specialized NOTAM number, an affected location, a keyword and the start time of the activity that could affect safety.

When did NOTAMs begin?

While many travelers might be learning about the system because of Wednesday’s mass delays, NOTAMs have been around for more than 75 years.

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In 1947, the Convention on International Civil Aviation, a specialized agency of the United Nations that coordinated international air travel, agreed to begin issuing NOTAMs through telecommunications to assist with airplane safety. Originally known as the Notice to Airmen system, NOTAMs were modeled after Notice to Mariners. That system advised ship captains of hazards in navigating the high seas, according to the FAA.

When are NOTAMs issued?

NOTAMs can be issued by authorities for a variety of reasons, including potential hazards such as parachute jumps, air shows and glider or micro-light flying, and warning of flights carrying heads of state. Closed runways and taxiways, unserviceable radio navigational aids or military exercises causing airspace restrictions also could trigger the issuing of NOTAMs.

It also doesn’t take much for a NOTAM to flag a hazard that could interfere with flight operations. The erection of temporary obstacles, such as cranes, by an airfield or airport, as well as lights that cannot be serviced on tall obstructions also are factors that could trigger NOTAMs.

Have there been any issues with NOTAMs?

Although the system has been largely effective for years, critics of the FAA often point to a 2017 incident to underscore a view that NOTAMs are “garbage.”

As Air Canada Flight 759 tried to land in San Francisco in July 2017, the plane nearly crashed into four other airliners. The pilots of Flight 759 were able to avoid disaster after trying to land on a taxiway that was misidentified as a runway. The runway the pilots were looking for had been closed — and that information was buried in a NOTAM they had received, according to investigators.

The National Transportation Safety Board found at the conclusion of its investigation in 2018 that NOTAMs were ignored by pilots since they were unintelligible. Robert Sumwalt, then the chairman of the NTSB, described NOTAMs as “a bunch of garbage that nobody pays any attention to,” according to Reuters.

The fallout from the investigation led the International Civil Aviation Organization to reform the NOTAM system, allowing the notices to be better organized and deciphered through electronic flight planning apps.