NEW YORK: The safety system at the heart of Wednesday's temporary nationwide US flight grounding provides pilots with notifications of unusual conditions that could affect travel.
The Notice to Air Missions (NOTAM) is a safety system distinct from air traffic control, which tracks plane location in order to prevent crashes.
A NOTAM "is a notice containing information essential to personnel concerned with flight operations but not known far enough in advance to be publicized by other means," according to the Federal Aviation Administration website.
"It states the abnormal status of a component of the National Airspace System -- not the normal status."
Aviation experts say such alerts can be highly important, such as the notification of a closed runway, or if there is a problem with ground-based signals used to land the plane.
But the alerts can be numerous and may contain less vital information, such as the presence of construction cranes near an airport, or of a crew mowing a lawn.
The notices are written in a shorthand style "characterized by the use of specialized contractions," according to an FAA handbook for pilots.
"Contractions are imperative to the NOTAM structure because they make communication more efficient and allow computer systems to parse important words."
The system dates to 1947 and was long known as the "Notice to Airmen." The FAA changed the name in December 2021 to be "inclusive of all aviators and missions," the agency said.
Transportation Secretary Pete Buttigieg said the agency had not ruled out the possibility of a "nefarious" actor causing Wednesday's outage -- which forced the delay of thousands of US flights -- but that there was no evidence so far pointing in that direction.
Buttigieg told MSNBC that the investigation will focus in part on why backup systems were not able to avert a national outage.
Some experts have speculated that the problem may stem from a software update that was not well received.