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A Notice to Airmen (NOTAM) is a notice filed with an aviation authority to alert aircraft pilots of potential hazards along a flight route or at a location that could affect the safety of the flight. NOTAMs are unclassified notices or advisories distributed by means of telecommunication that contain information concerning the establishment, conditions or change in any aeronautical facility, service, procedure or hazard, the timely knowledge of which is essential to personnel and systems concerned with flight operations. NOTAMs are created and transmitted by government agencies and airport operators under guidelines specified by Annex 15: Aeronautical Information Services of the Convention on International Civil Aviation (CICA). The term NOTAM came into common use rather than the more formal Notice to Airmen following the ratification of the CICA, which came into effect on 4 April 1947. Notices to Airmen were normally published in a regular publication by each country's air authorities (e.g., in Flight Magazine in the UK). A number of developments and amendments to the CICA have resulted in the more automated system available today.
A NOTAM is filed with an aviation authority to alert aircraft pilots of any hazards en route or at a specific location. The authority in turn provides a means of disseminating relevant NOTAMs to pilots.
NOTAMs are issued (and reported) for a number of reasons, such as:
- hazards such as air shows, parachute jumps, kite flying, lasers, rocket launches, etc.
- flights by important people such as heads of state (sometimes referred to as temporary flight restrictions, TFRs)
- closed runways
- inoperable radio navigational aids
- military exercises with resulting airspace restrictions
- inoperable lights on tall obstructions
- temporary erection of obstacles near airfields (e.g., cranes)
- passage of flocks of birds through airspace (a NOTAM in this category is known as a BIRDTAM)
- notifications of runway/taxiway/apron status with respect to snow, ice, and standing water (a SNOWTAM)
- notification of an operationally significant change in volcanic ash or other dust contamination (an ASHTAM)
- software code risk announcements with associated patches to reduce specific vulnerabilities
Aviation authorities typically exchange NOTAMs over AFTN circuits.
Software is available to allow pilots to identify NOTAMs near their intended route or at the intended destination. Some complain that the volume and increasing triviality of NOTAMs has reduced their usefulness. 
In the U.S. Air Force information technology enterprise, C4 NOTAMs (Command, Control, Communications, and Computer Notices to Airmen) are notices of new or updated Air Force Network Operating Instructions (AFNOIs). Often, these notices serve to direct Air Force computer administrators to install security updates or change the configuration of computer systems.
In July 2017, Air Canada Flight 759 nearly crashed into four other airliners as it attempted to land on a San Francisco taxiway misidentified as a runway: the next runway was closed but the information was buried in the Notam. In September 2018, the NTSB stated Notams were unintelligible and ignored, and recommended a more effective information presentation for better relevance. Flight planning applications for electronic flight bag can help decipher and better organize Notams, as from Foreflight or Jeppesen.
The following describes ICAO NOTAMs. NOTAMs are published using all upper case letters which are claimed by some to make NOTAMs difficult to read. Note that some countries such as the United States may diverge from the following ICAO standards.
- The first line contains NOTAM identification (series, sequence number, and year of issue), the type of operation (NEW, REPLACE, or CANCEL), as well as a reference to a previously-issued NOTAM (for NOTAMR and NOTAMC only).
- The "Q" line holds information about who the NOTAM affects along with a basic NOTAM description. This line can be encoded/decoded from tables defined by ICAO. This allows NOTAMs to be displayed electronically
- The "A" line is the ICAO code of the affected aerodrome or FIR for the NOTAM. The area of influence of the NOTAM can be several hundreds of kilometres away from the originating aerodrome.
- The "B" line contains the start date and time, the "C" line contains the finish date and time of the NOTAM. The date is in the format YY/MM/DD and the times are given in Universal Co-ordinated Time; also known as UTC or Zulu time.
- Sometimes a "D" line may be present. This gives a miscellaneous diurnal time for the NOTAM if the hours of effect are less than 24 hours a day, e.g., parachute dropping exercises tend to occur for short periods of a few hours during the day, but may be repeated over many days.
- The "E" line is the full NOTAM description. It is in English but can be heavily abbreviated. These abbreviations can be encoded/decoded by tables defined by ICAO.
- When present, "F" and "G" lines detail the height/altitude restrictions of the NOTAM. Typically SFC means surface height or ground level and UNL is unlimited height. Other heights are given in feet or flight level or a combination of the two.
- A1234/06 NOTAMR A1212/06
- E)DUE WIP TWY B SOUTH CLSD BTN 'F' AND 'R'. TWY 'R' CLSD BTN 'A' AND 'B' AND DIVERTED VIA NEW GREEN CL AND BLUE EDGE LGT. CTN ADZ
This decodes into the following:
- SERIES and NUMBER : A1234 issued in 2006
- NATURE OF THE NOTAM : Replacing NOTAM 1212 issued in 2006
- FIR: EGTT (LONDON FIR)
- SUBJECT: Taxiway (MX)
- CONDITION: Closed (LC)
- TRAFFIC: NOTAM issued for IFR (I) flights and VFR flights (V)
- PURPOSE: NOTAM selected for immediate attention of flight crew members (N)
- PURPOSE: NOTAM selected for PIB entry (B)
- PURPOSE: NOTAM concerning flight operations (O)
- SCOPE: Aerodrome
- LIMITS: FL 000 to FL 999 (000/999)
- GEOGRAPHICAL LOCATION : 51°29' N 000° 28' W
- OPERATIONAL RADIUS OF THE NOTAM : 5 NM
- AERODROME : London Heathrow (EGLL)
- FROM: 05:00 UTC 5 September 2006
- UNTIL:05:00 UTC 30 April 2007
- CATEGORY: Aerodromes, Air Routes, and Ground Aids
- DESCRIPTION: Due to work in progress, taxiway "B South" is closed between "F" and "R". Taxiway "R" is closed between "A" and "B" and is diverted via a new green centre line and blue edge lighting. Caution advised.
U.S. domestic NOTAMs
- NOTAM (D) or distant NOTAMs
- A NOTAM (D) information is disseminated for all navigational facilities that are part of the National Airspace System (NAS), all public use airports, seaplane bases, and heliports listed in the Airport/Facility Directory (A/FD) (e.g., such information as whether or not an airport or a certain facility is usable). NOTAM (D) information includes, among other topics, such data as taxiway closures, personnel and equipment near or crossing runways, and airport lighting aids that do not affect instrument approach criteria, such as VASI.
- Flight Data Center (FDC) NOTAMs
- The National Flight Data Center will issue these NOTAMs when it becomes necessary to disseminate information that is regulatory in nature, and they contain such things as amendments to published IAPs and other current aeronautical charts. They are also used to advertise temporary flight restrictions caused by such things as natural disasters or large-scale public events that may generate congestion of air traffic over a site.
- Pointer NOTAMs
- NOTAMs issued by a flight service station to highlight or point out another NOTAM, such as an FDC or NOTAM (D) NOTAM. This type of NOTAM will assist users in cross-referencing important information that may not be found under an airport or NAVAID identifier.
- Special activity airspace (SAA) NOTAMs
- SAA NOTAMs are issued when SAA (the term "SAA" includes SUA, as well as instrument and visual military training routes, aerial refueling tracks and anchors) will be active outside the published schedule times and when required by the published schedule.
- Military NOTAMs
- NOTAMs pertaining to U.S. Air Force, Army, Marine, and Navy navigational aids/airports that are part of the NAS.
- Chambers, Dan (February 10, 2010). "Flight School 101: What is a NOTAM?". College of Aeronautical Science & Technology. Retrieved February 9, 2013.
- AIR FORCE INSTRUCTION INTERSERVICE PUBLICATION 11-208 http://www.e-publishing.af.mil
- "Notices To Airmen", a 1921 NOTAM in Flight magazine
- FSB Flight Service Bureau, March 17, 2017. Retrieved 28 September, 2018
- HQ AFCA/GCLO. "Air Force Instruction 33-115, Volume 3: Air Force Network Operating Instructions" Air Force Departmental Publishing Office, 15 April 2004. Retrieved 11 May 2010.
- Stuart “Kipp” Lau (October 26, 2018). "AINsight: Notams Are Wall of Text and Bunch of Garbage". AIN online.
- AIM, 5–1–3 "Notice to Airmen (NOTAM) System" (August 22, 2013 revision)
- FAA Order JO 7930.2N, Notices to Airmen (NOTAM), effective 2013-10-01, accessed 2014-02-26
- European NOTAM website
- FAA NOTAM website
- FAA NOTAM website (with search capability that also allows retrieval of Letters to Airmen)
- DOD NOTAM website
- TFR NOTAM Visualizer (Temporary Flight Restrictions NOTAMs are visualized on 20+ maps)
- NOTAM on Skybrary
- US NOTAMS
- NOTAM decoder
- Free online NOTAM decoder
- http://ead.dhmi.gov.tr/ Turkish NOTAM display and database
- Turkish NOTAM display and database (notamtr)
- Learning the notices to airman -NOTAM
- Learning the notices to airman - D NOTAM
- The top 7 things you need to know about NOTAMs