Just before midnight on 7 July 2017, Air Canada Flight 759, an Airbus A320 inbound from Toronto, was cleared to land on runway 28R at San Francisco International Airport. The crew lined up instead with taxiway C, where four airliners sat waiting to take off. The A320 descended to 100 feet above the ground over the first of them and reached a minimum of about 60 feet over the second before the go-around finally took hold.

The warning that could have prevented it had been in the crew's paperwork since Toronto. The parallel runway, 28L, was closed, and the line saying so, "RWY 10R/28L CLSD", sat on page 8 of a 27-page flight release. It was a NOTAM.

NOTAMs are the least glamorous documents in aviation and among the most important. Every pilot is expected to read the ones that touch their flight, from a light-aircraft owner hopping between grass strips to an airline captain crossing an ocean. Here is what they are, how to decode one, why safety investigators have called them garbage, and how their computer system once stopped every departure in the United States.

What a NOTAM Actually Is

The International Civil Aviation Organization defines a NOTAM, in the wording reproduced by the safety encyclopedia SKYbrary from ICAO Annex 11, as "a notice containing information concerning the establishment, condition or change in any aeronautical facility, service, procedure or hazard, the timely knowledge of which is essential to personnel concerned with flight operations."

The FAA's own definition is shorter and more practical: "a notice containing information essential to personnel concerned with flight operations but not known far enough in advance to be publicized by other means." The agency adds that a NOTAM states the abnormal status of a part of the National Airspace System, not its normal status. Charts and airport directories describe the world as it should be. NOTAMs describe what has changed.

In practice that covers closed runways and taxiways, unserviceable radio navigation aids, cranes put up near an airfield, unlit obstructions, parachute jumps and air shows, military exercises that close blocks of airspace, and flights by heads of state. Each one is small. Together, at a busy airport, they can run to pages.

A Mercury News animation reconstructs Air Canada 759's approach over the airliners waiting on taxiway C at San Francisco in July 2017.

Airmen, Air Missions, and Airmen Again

The acronym came into common use after the Chicago Convention, which founded the modern ICAO system, took effect on 4 April 1947. On 2 December 2021 the FAA changed what the letters stood for in the United States, from Notice to Airmen to Notice to Air Missions, through a change to its NOTAM order 7930.2S. AOPA reported that the FAA described it as "the more applicable term", and that it also covered small drones and uncrewed free balloons.

Critics including Senator Ted Cruz called the change virtue signalling, according to AIN. On 10 February 2025 the FAA reversed it, with a notice reading: "Effective immediately, the term Notice to Air Missions (Notam) is being changed to Notice to Airmen (Notam)." ICAO had kept "Notice to Airmen" throughout, and the four letters pilots actually type never changed at all.

Anatomy of an ICAO NOTAM

The clearest way to learn the format is the FAA's own worked example: runway 04L/22R closed at Chicago O'Hare on 23 June 2021. The first line, B0667/21 NOTAMN, gives the series (B covers aerodrome maneuvering areas such as runways and taxiways), the number and year, and the action. N means new; R replaces an earlier NOTAM and C cancels one.

Then comes the Q line, which the FAA describes as coded information, coordinates and radius "for the automated filtering of NOTAMs". KZAU is the flight information region, here the Chicago Air Route Traffic Control Center. QMRLC is the NOTAM code: always a Q, then MR for runway and LC for closed. IV means it affects both instrument and visual flights, NBO flags it for immediate attention, pre-flight briefing and flight operations, A sets the scope as an aerodrome, and 000/999 are the default height limits used for airport NOTAMs. The last group, 4159N08754W005, places the centre at 41°59'N 087°54'W with a five-nautical-mile radius of influence.

After that the lettered items read almost like plain English. A) KORD is the airport. B) and C) are the start and end times in UTC, written year, month, day, hour, minute, so 2106231700 means 23 June 2021 at 1700Z. E) RWY 04L/22R CLSD is the message itself. Optional D) gives a schedule, while F) and G) set lower and upper limits for airspace NOTAMs.

The same closure in the FAA's US domestic format is a single line: !ORD 06/001 ORD RWY 04L/22R CLSD 2106231700-2106232300. The FAA says it is working to make US NOTAMs comply with ICAO standards, which is why American pilots increasingly meet both styles. Either way, as the FAA puts it, "NOTAMs have a unique language using special contractions to make communication more efficient."

TFRs, Military Airspace and Closed Skies

Some NOTAMs are not just information but law. In the United States, Temporary Flight Restrictions are issued as FDC NOTAMs, the regulatory category that also covers changes to instrument approaches and airways. TFRs, airway changes and laser activity are filed as Center Area NOTAMs under the air route traffic control center that owns the airspace, so a pilot searching only under the destination airport can miss them.

Miss a TFR and the consequence can arrive with afterburners. Afterburner has covered a run of NORAD intercepts in which F-16 fighters met light aircraft that had strayed into restricted airspace, from Maryland and Bedminster to Chicago, where F-16s fired flares at aircraft during a presidential visit.

Military airfields publish NOTAMs too, and they read like orders of the day. On the morning of the 2023 outage, the FAA's public search for Nellis Air Force Base in Nevada listed exercise aircraft that had to arrange prior permission, limited transient support, obstruction lights out of service, and a blunt line stating the base was for official business only.

The Morning the NOTAM System Stopped America

That banner was the visible tip of a national problem. The US NOTAM system began failing on 10 January 2023. By the next morning the FAA had ordered airlines to pause all domestic departures until 9 a.m. Eastern Time "to allow the agency to validate the integrity of flight and safety information." Flights already airborne continued.

Departures resumed at Newark and Atlanta first, and by 8:50 a.m. Eastern the FAA announced the ground stop had been lifted. By noon, FlightAware had counted about 6,988 delayed flights and more than 1,100 cancellations, NPR reported. The pause was widely described as the first nationwide ground stop since 11 September 2001, although NPR noted that claim was unconfirmed.

That evening the FAA said its preliminary work had traced the outage "to a damaged database file" and that there was no evidence of a cyber attack. The fuller explanation came eight days later.

There was still no sign of a cyber attack. The cause, the FAA said on 19 January, was a maintenance job that went wrong while contractors tried to keep two copies of the database in step.

The FAA has since built a replacement. Its new NOTAM Management Service, a cloud-hosted system, began operations at the end of September 2025, and the agency set late spring 2026 as its target for moving to a single-source NOTAM service.

Air Canada 759 and the “Garbage” Problem

Back in San Francisco, the National Transportation Safety Board found that the probable cause of the 2017 incident was the crew's misidentification of taxiway C as the landing runway, resulting from their lack of awareness that the parallel runway was closed "due to their ineffective review of NOTAM information before the flight and during the approach briefing." Air Canada's ineffective presentation of approach procedure and NOTAM information was a contributing factor.

The NTSB looked hard at how that information reached the cockpit. The closure NOTAM sat on page 8 of the 27-page release, in the middle of the package, despite bold type and a red NEW tag. The investigators cited the serial position effect: people remember the first and last items in a list better than the middle ones.

The airport information that arrived by datalink before landing was no better. The ATIS message, as displayed in the cockpit, was 14 continuous lines in capital letters, with the runway closure split across the end of line 8 and the start of line 9.

At the NTSB board meeting in September 2018, chairman Robert Sumwalt read out a verbose NOTAM restricting part of a taxiway to aircraft with a wingspan of 214 feet or less, and asked, as AIN reported: "Why is this even on there?"

Vice Chairman Bruce Landsberg went further in a concurring statement. He wrote: "Concerns about legal liability rather than operational necessity, drive the current system to list every possible Notice to Airmen (Notam) that could, even under the most unlikely circumstance, affect a flight." The result, in his words, is "an impossibly heavy burden on individual pilots, crews and dispatchers."

The NTSB recommended that the FAA set up a group of human factors experts to work out how flight information should be organised, prioritised and presented so pilots actually retain what matters. ICAO has since run its own campaign to clean up the NOTAM flood.

OpsGroup's clip of the NTSB board meeting in which Robert Sumwalt dismissed the NOTAM system after the Air Canada 759 investigation.

How Pilots Read NOTAMs Today

Most crews no longer wade through raw teleprinter text. Flight-planning software and electronic flight bags filter and sort NOTAMs by route and airport, which is exactly what the Q line was designed to make possible. The FAA still reminds pilots to check 25 nautical miles either side of their full route so that relevant navigation-aid NOTAMs show up.

The principle is as old as the system itself: if it is in a NOTAM, the pilot is expected to know it. Air Canada 759 proved how close the gap between published and noticed can come to a catastrophe. About sixty feet, in fact.

Sources: NTSB Aircraft Incident Report AIR-18/01 (Air Canada 759), FAA (What is a NOTAM?, ICAO NOTAM Format Example, Order JO 7930.2 Appendix B, NOTAM statements of 11 and 19 January 2023), AIN, AOPA, NPR, SKYbrary, Wikipedia (NOTAM, 2023 FAA system outage)