International Civil Aviation Organization#Standards

In the early 20th Century, the International Telecommunication Union met to discuss and implement one of the first internationally agreed upon standards relating to aviation, country-specific prefixes for aircraft callsigns. The first convention was held in 1903 in Berlin, Germany, but no agreements were reached among the eight countries that attended. At the second convention in 1906, also held in Berlin, twenty-seven countries attended.{{Cite web |url=http://www.airhistory.org.uk/gy/reg_index.html |title=Golden Years of Aviation – Register index |access-date=20 October 2019 |archive-url=https://web.archive.org/web/20191222220837/http://www.airhistory.org.uk/gy/reg_index.html |archive-date=22 December 2019 |url-status=live }} The third convention, held in London in 1912, allocated the first radio callsigns for use by aircraft. Following this, at the Paris Convention of 1919, a forerunner to ICAO named ICAN was established, the International Commission for Air Navigation. ICAN continued to operate until 1945.{{cite web |url=http://www.goldenyears.ukf.net/reg_index.htm |title=Registrations |publisher=Golden Years of Aviation |access-date=11 February 2011 |archive-url=https://web.archive.org/web/20110130183900/http://www.goldenyears.ukf.net/reg_index.htm |archive-date=30 January 2011 |url-status=dead}}{{cite web |url=http://www.goldenyears.ukf.net/reg_1912.htm |title=1912 Radio Callsign prefixes |publisher=Golden Years of Aviation |access-date=11 February 2011 |archive-url=https://web.archive.org/web/20110101190356/http://www.goldenyears.ukf.net/reg_1912.htm |archive-date=1 January 2011 |url-status=dead}}

The Convention on International Civil Aviation, also known as the Chicago Convention, in Chicago, was signed by 52 countries on 7 December 1944. Under its terms, a Provisional International Civil Aviation Organization was to be established, to be replaced in turn by a permanent organization when twenty-six countries ratified the convention. PICAO began operating on 6 June 1945, replacing ICAN. The 26th country ratified the convention on 5 March 1947 and, consequently, PICAO was disestablished on 4 April 1947 and replaced by ICAO, which began operations the same day.{{Citation needed|date=October 2024}}

In October 1947, ICAO became an agency of the United Nations under its Economic and Social Council (ECOSOC).{{cite web|url=https://www.icao.int/about-icao/History/Pages/default.aspx|title=icao.int International Civil Aviation Organization History|access-date=28 July 2017|archive-url=https://web.archive.org/web/20170729011700/https://www.icao.int/about-icao/History/Pages/default.aspx|archive-date=29 July 2017|url-status=live}}

In April 2013, Qatar offered to serve as the new permanent seat of the Organization. Qatar promised to construct a massive new headquarters for ICAO and to cover all moving expenses, stating that Montreal "was too far from Europe and Asia", "had cold winters", was hard to attend due to the Canadian government's slow issuance of visas, and that the taxes imposed on ICAO by Canada were too high.[https://www.cbc.ca/news/politics/baird-fighting-tooth-and-nail-to-keep-un-aviation-office-in-montreal-1.1311536 Baird fighting 'tooth and nail' to keep UN aviation office in Montreal], CBC News, 2 May 2013. According to The Globe and Mail, Qatar's invitation was at least partly motivated by the pro-Israel foreign policy of Canadian Prime Minister Stephen Harper.[https://www.theglobeandmail.com/news/world/disgruntled-arab-states-look-to-strip-canada-of-un-agency/article11672346/ Disgruntled Arab states look to strip Canada of UN agency] {{Webarchive|url=https://web.archive.org/web/20170504035124/http://www.theglobeandmail.com/news/world/disgruntled-arab-states-look-to-strip-canada-of-un-agency/article11672346/ |date=4 May 2017 }} by Campbell Clark, The Globe and Mail, 2 May 2013.[https://www.theglobeandmail.com/commentary/canada-now-paying-the-price-for-bairds-misstep-into-east-jerusalem/article11730522/ Canada now paying the price for Baird's misstep into East Jerusalem] {{Webarchive|url=https://web.archive.org/web/20130511220230/http://www.theglobeandmail.com/commentary/canada-now-paying-the-price-for-bairds-misstep-into-east-jerusalem/article11730522/ |date=11 May 2013 }} by Michael Bell, The Globe and Mail, 6 May 2013.

Approximately a month later, Qatar withdrew its bid after a separate proposal to the ICAO's governing council to move the ICAO triennial conference to Doha was defeated by a vote of 22–14.[https://montrealgazette.com/business/ICAO+stays+Montreal+after+Qatar+stumbles/8433119/story.html ICAO stays in Montreal after Qatar stumbles] {{Webarchive|url=https://web.archive.org/web/20130603093543/http://www.montrealgazette.com/business/ICAO+stays+Montreal+after+Qatar+stumbles/8433119/story.html |date=3 June 2013 }} by François Shalom, The Montreal Gazette, 24 May 2013.{{cite news|title=Lobbying saved Montreal's UN aviation agency, Paradis says|url=https://www.cbc.ca/news/politics/lobbying-saved-montreal-s-un-aviation-agency-paradis-says-1.1396643|access-date=24 May 2013|publisher=CBC News|date=24 May 2013|archive-url=https://web.archive.org/web/20130525033122/http://www.cbc.ca/news/politics/story/2013/05/24/pol-icao-montreal-un-aviation-qatar-baird.html|archive-date=25 May 2013|url-status=live}}[http://www.icao.int/Newsroom/Pages/Qatar-withdraws-offer-to-host-ICAO-permanent-seat.aspx Qatar Withdraws Offer to Host ICAO Permanent Seat] {{Webarchive|url=https://web.archive.org/web/20130613133651/http://www.icao.int/Newsroom/Pages/Qatar-withdraws-offer-to-host-ICAO-permanent-seat.aspx |date=13 June 2013 }}, ICAO Newsroom, 24 May 2013.

In January 2020, ICAO blocked several Twitter users, including think-tank analysts, U.S. Congressional staff, and journalists, who mentioned Taiwan in tweets related to ICAO. Many of the tweets were related to the COVID-19 pandemic and Taiwan's exclusion from ICAO safety and health bulletins due to pressure from China. In response, ICAO issued a tweet stating that publishers of "irrelevant, compromising and offensive material" would be "precluded".{{cite web |first2=Jerome |last2=Taylor |first1=Sean |last1=Chang |title=Twitter row over Taiwan virus response hits UN aviation body |url=https://news.yahoo.com/twitter-row-over-taiwan-virus-response-hits-un-053211089.html |publisher=Yahoo! News |agency=Agence France-Presse |date=29 January 2020 |access-date=30 January 2020 |archive-date=30 January 2020 |archive-url=https://web.archive.org/web/20200130052909/https://news.yahoo.com/twitter-row-over-taiwan-virus-response-hits-un-053211089.html |url-status=live }}{{cite web |last1=Pei-ju |first1=Teng |title=UN's aviation agency blocks Twitter accounts mentioning 'Taiwan' |url=https://www.taiwannews.com.tw/en/news/3865735 |work=Taiwan News |date=28 January 2020 |access-date=28 January 2020 |archive-date=28 January 2020 |archive-url=https://web.archive.org/web/20200128093210/https://www.taiwannews.com.tw/en/news/3865735 |url-status=live }}{{cite web |last1=Grundy |first1=Tom |title=Wuhan coronavirus: UN aviation body blocks users who raise issue of Taiwan's inclusion on Twitter |url=https://www.hongkongfp.com/2020/01/28/wuhan-coronavirus-un-aviation-body-blocks-users-raise-issue-taiwans-inclusion-twitter/ |work=Hong Kong Free Press |access-date=28 January 2020 |archive-url=https://web.archive.org/web/20200128034804/https://www.hongkongfp.com/2020/01/28/wuhan-coronavirus-un-aviation-body-blocks-users-raise-issue-taiwans-inclusion-twitter/ |archive-date=28 January 2020 |url-status=live |date=28 January 2020 }}

Since that action, the organization has followed a policy of blocking anyone asking about it.{{cite web |last1=Allen-Ebrahimian |first1=Bethany |title=UN aviation agency blocks critics of Taiwan policy on Twitter |url=https://www.axios.com/as-virus-spreads-un-agency-blocks-critics-taiwan-policy-on-twitter-e8a8bce6-f31a-4f41-89e0-77d919109887.html |work=Axios |date=27 January 2020 |access-date=28 January 2020 |archive-url=https://web.archive.org/web/20200127202341/https://www.axios.com/as-virus-spreads-un-agency-blocks-critics-taiwan-policy-on-twitter-e8a8bce6-f31a-4f41-89e0-77d919109887.html |archive-date=27 January 2020 |url-status=live }}{{cite news |last1=Smith |first1=Nicola |title=UN aviation body criticised for 'silencing' critics over Taiwan's role in virus fight |url=https://www.telegraph.co.uk/news/2020/01/28/un-aviation-body-criticised-silencing-critics-taiwans-role-virus/ |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/news/2020/01/28/un-aviation-body-criticised-silencing-critics-taiwans-role-virus/ |archive-date=12 January 2022 |url-access=subscription |url-status=live |newspaper=The Telegraph |access-date=28 January 2020|date=28 January 2020 }}{{cbignore}}

The United States House Committee on Foreign Affairs harshly criticized ICAO's perceived failure to uphold principles of fairness, inclusion, and transparency by silencing non-disruptive opposing voices. Senator Marco Rubio also criticized the move.{{cite web |author=Staff Writer |title=US House committee blasts ICAO over Taiwan issue |url=http://www.taipeitimes.com/News/front/archives/2020/01/29/2003729989 |work=Taipei Times |access-date=28 January 2020 |archive-url=https://web.archive.org/web/20200128213221/http://www.taipeitimes.com/News/front/archives/2020/01/29/2003729989 |archive-date=28 January 2020 |url-status=live }} The Taiwanese Ministry of Foreign Affairs (MOFA) and legislators criticized the move, with MOFA head Jaushieh Joseph Wu tweeting in support of those blocked.

In January 2020, Anthony Philbin, Chief of Communications for the ICAO Secretary General, defended ICAO's actions, stating, 'We felt completely justified in taking steps to protect the integrity of the information and discussions that our followers reasonably expect from our feeds.' In exchanges with the International Flight Network, Philbin refused to acknowledge the existence of Taiwan.{{cite web |last1=Wert |first1=Jakob |title=ICAO excludes Taiwan from cooperation amid Coronavirus, rejects criticism |url=https://www.ifn.news/posts/icao-excludes-taiwan-from-cooperation-amid-coronavirus-rejects-criticism/ |work=International Flight Network |access-date=28 January 2020 |archive-url=https://web.archive.org/web/20200128134227/https://www.ifn.news/posts/icao-excludes-taiwan-from-cooperation-amid-coronavirus-rejects-criticism/ |archive-date=28 January 2020 |url-status=live |date=28 January 2020 }}

On 1 February 2020, the United States Department of State issued a press release heavily criticizing ICAO's actions, characterizing them as "outrageous, unacceptable, and not befitting of a UN organization."{{cite press release |first=Morgan |last=Ortagus |title=ICAO's Outrageous Practice of Blocking Twitter Users Who Reference Taiwan |url=https://2017-2021.state.gov/icaos-outrageous-practice-of-blocking-twitter-users-who-reference-taiwan/index.html |work=United States Department of State |access-date=1 April 2023 |date=1 February 2020 |archive-date=1 April 2023 |archive-url=https://web.archive.org/web/20230401193541/https://2017-2021.state.gov/icaos-outrageous-practice-of-blocking-twitter-users-who-reference-taiwan/index.html |url-status=live }}{{cite web |last1=Tiezzi |first1=Shannon |title=Amid Coronavirus Panic, Taiwan Scrambles to Distinguish Itself From China |url=https://thediplomat.com/2020/02/amid-coronavirus-panic-taiwan-scrambles-to-distinguish-itself-from-china/ |work=The Diplomat |date=4 February 2020 |access-date=4 February 2020 |archive-date=3 February 2020 |archive-url=https://web.archive.org/web/20200203175043/https://thediplomat.com/2020/02/amid-coronavirus-panic-taiwan-scrambles-to-distinguish-itself-from-china/ |url-status=live }}

On May 2, 2025, the ICAO Council expressed grave concern over ongoing Global Navigation Satellite System (GNSS) radio frequency interference in the Incheon Flight Information Region (FIR), incidents that have persisted since October 2, 2024, and are attributed to North Korea, officially known as the Democratic People's Republic of Korea (DPRK). The Council emphasized that such interference endangers international air navigation safety and violates the principles of the Chicago Convention. It strongly urged the DPRK to adhere to its international obligations and prevent future occurrences. Given the severity of the situation, the Council is considering reporting the matter to the 42nd Session of the ICAO Assembly in September 2025, as per Article 54(k) of the Convention, and will continue to monitor developments closely.{{cite news |title= ICAO Council condemns radio frequency interference affecting civil aviation safety, urges DPRK to stop disruptive activities |url= https://www.icao.int/Newsroom/Pages/ICAO-Council-condemns-radio-frequency-interference-TBC.aspx |accessdate=4 May 2025 |agency=ICAO |date=2 May 2025}}

The 9th edition of the Convention on International Civil Aviation includes modifications from years 1948 up to 2006. ICAO refers to its current edition of the convention as the Statute and designates it as ICAO Document 7300/9. The convention has 19 Annexes that are listed by title in the article Convention on International Civil Aviation.{{cite web|url=http://www.icao.int/safety/SafetyManagement/Pages/Annex-19,-1st-Edition---Executive-summary.aspx|title=Annex 19 on Security Management|access-date=31 May 2017|url-status=dead|archive-url=https://web.archive.org/web/20131210131909/http://www.icao.int/safety/SafetyManagement/Pages/Annex-19%2C-1st-Edition---Executive-summary.aspx|archive-date=10 December 2013}}

File:ICAO.png

{{As of|2019|04}}, there are 193 ICAO members, consisting of 192 of the 193 UN members (all but Liechtenstein, which lacks an international airport), plus the Cook Islands.{{cite web|url=http://www.icao.int/MemberStates/Member%20States.French.pdf|title=Member States|publisher=ICAO|access-date=2025-02-19|archive-url=https://web.archive.org/web/20190607062702/http://www.icao.int/MemberStates/Member%20States.English.pdf|archive-date=7 June 2019|url-status=live}}[http://www.sudantribune.com/spip.php?article40710 South Sudan becomes 191st member of ICAO – Sudan Tribune: Plural news and views on Sudan]. Sudan Tribune. Retrieved 2013-07-12. {{webarchive |url=https://web.archive.org/web/20150323225722/http://www.sudantribune.com/spip.php?article40710 |date=23 March 2015 }}

Despite Liechtenstein not being a direct party to ICAO, its government delegated Switzerland to enter into the treaty on its behalf in 1947, and the treaty is applicable in the territory of Liechtenstein.{{cite web|url=http://www.icao.int/publications/Documents/chicago.pdf|title=Member States.English.pdf|publisher=ICAO|access-date=2014-07-20|archive-url=https://web.archive.org/web/20150605144229/http://www.icao.int/publications/Documents/chicago.pdf|archive-date=5 June 2015|url-status=live}}

The Minister of Switzerland made the following statement in the note transmitting the Swiss Instrument of Ratification:

"My Government has instructed me to notify you that the authorities in Switzerland have agreed with the authorities in the Principality of Liechtenstein that this Convention will be applicable to the territory of the Principality as well as to that of the Swiss Confederation, as long as the Treaty of 29 March 1923 integrating the whole territory of Liechtenstein with the Swiss customs territory will remain in force".

The Republic of China was a founding member of ICAO. Following its retreat to Taiwan, it was eventually replaced by the People's Republic of China as the legal representative of China in 1971.

In 2013, Taiwan was for the first time invited to attend the ICAO Assembly, at its 38th session, as a guest under the name of "Chinese Taipei". {{As of|2019|09}}, it has not been invited to participate again, due to renewed PRC pressure.{{cite web |last1=Jennings |first1=Ralph |title=UN Aviation Agency Rejects Taiwan: Here's Why It Matters |url=https://www.forbes.com/sites/ralphjennings/2016/09/28/un-aviation-agency-rejects-taiwan-3-losses/ |work=Forbes |access-date=28 January 2020 |archive-url=https://web.archive.org/web/20181125133514/https://www.forbes.com/sites/ralphjennings/2016/09/28/un-aviation-agency-rejects-taiwan-3-losses/#1055f2b33c72 |archive-date=25 November 2018 |url-status=live }}{{cite web |last1=Joseph Yeh |first1=Chiang Chin-yeh and |title=Taiwan's absence from ICAO creates gap in aviation network: CAA |url=https://focustaiwan.tw/politics/201909240005 |website=focustaiwan.tw |date=24 September 2019 |publisher=Focus Taiwan |access-date=28 January 2020 |archive-date=4 July 2021 |archive-url=https://web.archive.org/web/20210704071127/https://focustaiwan.tw/politics/201909240005 |url-status=live }}{{cite web |agency=Reuter |title=Sorry, you're not invited: UN aviation agency snubs Taiwan in sign of pressure from Beijing |url=https://www.scmp.com/news/china/policies-politics/article/2021950/sorry-youre-not-invited-un-aviation-agency-snubs-taiwan |work=South China Morning Post|access-date=28 January 2020 |archive-url=https://web.archive.org/web/20191217081407/https://www.scmp.com/news/china/policies-politics/article/2021950/sorry-youre-not-invited-un-aviation-agency-snubs-taiwan |archive-date=17 December 2019 |url-status=live |date=23 September 2016 }}{{cite web |last1=Sutton |first1=David |title=International Civil Aviation Organization Shuts out Taiwan |url=https://thediplomat.com/2016/09/international-civil-aviation-organization-shuts-out-taiwan/ |website=thediplomat.com |publisher=The Diplomat |access-date=28 January 2020 |archive-url=https://web.archive.org/web/20200128111702/https://thediplomat.com/2016/09/international-civil-aviation-organization-shuts-out-taiwan/ |archive-date=28 January 2020 |url-status=live }}

The host government, Canada, supports Taiwan's inclusion in ICAO. Support also comes from Canada's commercial sector with the president of the Air Transport Association of Canada saying in 2019 that "It's about safety in aviation so from a strictly operational and non-political point of view, I believe Taiwan should be there."{{cite news |last1=Robert Fife |first1=Steven Chase and |title=Canada backing Taiwan's effort to gain invitation to International Civil Aviation Organization |url=https://www.theglobeandmail.com/politics/article-canada-backing-taiwans-effort-to-gain-invitation-to-international/ |work=The Globe and Mail|access-date=28 January 2020 |archive-url=https://web.archive.org/web/20190913011708/https://www.theglobeandmail.com/politics/article-canada-backing-taiwans-effort-to-gain-invitation-to-international/ |archive-date=13 September 2019 |url-status=live }}

File:ICAO Council Chamber 2013.jpg

The ICAO Council is elected by the Assembly every three years and consists of 36 members elected in three groups. The present council was elected in October 2022.{{cite web|url=https://www.icao.int/Newsroom/Pages/ICAO-Assembly-elects-new-Council-for-threeyear-term.aspx|title=ICAO Assembly elects new Council Member States for three-year term|website=International Civil Aviation Organization|date=4 October 2022|access-date=7 October 2022|archive-date=1 June 2023|archive-url=https://web.archive.org/web/20230601085937/https://www.icao.int/Newsroom/Pages/ICAO-Assembly-elects-new-Council-for-threeyear-term.aspx|url-status=live}}

The structure of the present Council is as follows:

File:ICAO ANC meeting room 2013.jpg

The Air Navigation Commission (ANC) is the ICAO Council technical executive body in charge of 17 of the 19 Annexes to the Chicago Convention. ANC develops and recommend ICAO minimal standards that are related to these Annexes. To review and/or finalize the ongoing developments the commission meets for three sessions per year. Each session normally considers a number of documents being developments of ANC expert Panels. The ANC is composed of nineteen commissioners nominated by ICAO States in various aviation domains. However, legally these commissioners do not represent the interest of their State or any particular State or region. They have to conduct independently in the interest of the entire international civil aviation community. Additionally, several other representatives from ICAO States and up to eight members from the civil aviation industry may be invited to take part in ANC meetings as observers.{{Cite web |title=Air Navigation Commission |url=https://www.ifatca.org/about-ifatca/icao-activities/air-navigation-commission/ |access-date=2023-02-25 |website=IFATCA |language=en-GB |archive-date=25 February 2023 |archive-url=https://web.archive.org/web/20230225100553/https://www.ifatca.org/about-ifatca/icao-activities/air-navigation-commission/ |url-status=live }}{{Cite web |title=Air Navigation Commission |url=https://www.icao.int/about-icao/AirNavigationCommission/Pages/default.aspx |access-date=2023-02-25 |website=ICAO |archive-date=25 February 2023 |archive-url=https://web.archive.org/web/20230225100551/https://www.icao.int/about-icao/AirNavigationCommission/Pages/default.aspx |url-status=live }}

{{further|Standards And Recommended Practices}}

ICAO also standardizes certain functions for use in the airline industry, such as the Aeronautical Message Handling System (AMHS). This makes it a standards organization.

Each country should have an accessible Aeronautical Information Publication (AIP), based on standards defined by ICAO, containing information essential to air navigation. Countries are required to update their AIP manuals every 28 days and so provide definitive regulations, procedures and information for each country about airspace and airports. ICAO's standards also dictate that temporary hazards to aircraft must be regularly published using NOTAMs.

ICAO defines an International Standard Atmosphere (also known as ICAO Standard Atmosphere), a model of the standard variation of pressure, temperature, density, and viscosity with altitude in the Earth's atmosphere. This is useful in calibrating instruments and designing aircraft.{{cite book |title=Manual of the ICAO Standard Atmosphere: extended to 80 kilometres (262,500 feet) |year=1993 |publisher=ICAO |location=Montreal |isbn=92-9194-004-6 |url=http://legacy.icao.int/cgi/ISBN_txt.pl?16 |edition=3rd |access-date=2012-09-06 |language=en, fr, es, ru |format=CD-ROM |archive-url=https://web.archive.org/web/20121206111249/http://legacy.icao.int/cgi/ISBN_txt.pl?16 |archive-date=6 December 2012 |url-status=dead}} The standardized pressure is also used in calibrating instruments in-flight, particularly above the transition altitude.

ICAO is active in infrastructure management, including communication, navigation and surveillance / air traffic management (CNS/ATM) systems, which employ digital technologies (like satellite systems with various levels of automation) in order to maintain a seamless global air traffic management system.{{cite web|title=Infrastructure Management|url=http://www.icao.int/sustainability/Pages/eap-im-cns-atm.aspx|publisher=ICAO|access-date=2012-09-06|archive-url=https://web.archive.org/web/20121206115759/http://www.icao.int/sustainability/Pages/eap-im-cns-atm.aspx|archive-date=6 December 2012|url-status=live}}

ICAO has published standards for machine-readable passports.{{cite web |title=Welcome to the ICAO Machine Readable Travel Documents Programme |url=http://www.icao.int/Security/mrtd/Pages/default.aspx |publisher=ICAO |access-date=2012-09-06 |archive-url=https://web.archive.org/web/20120829034033/http://www.icao.int/Security/mrtd/Pages/default.aspx |archive-date=29 August 2012 |url-status=live }} Machine-readable passports have an area where some of the information otherwise written in textual form is also written as strings of alphanumeric characters, printed in a manner suitable for optical character recognition, which enables border controllers and other law enforcement agents to process such passports more quickly without having to enter the information manually into a computer.

ICAO's technical standard for machine-readable passports is contained in Document 9303 Machine Readable Travel Documents.{{cite book |publisher=ICAO |title=Machine Readable Travel Documents, Document 9303 |year=2006 |edition=Sixth |url=http://www.icao.int/Security/mrtd/Pages/Document9303.aspx |access-date=2013-08-09 |archive-url=https://web.archive.org/web/20121211143634/http://www.icao.int/Security/mrtd/Pages/Document9303.aspx |archive-date=11 December 2012 |url-status=live }}

A more recent standard covers biometric passports. These contain biometrics to authenticate the identity of travellers. The passport's critical information is stored on a tiny RFID computer chip, much like information stored on smart cards. Like some smart cards, the passport book design calls for an embedded contactless chip that is able to hold digital signature data to ensure the integrity of the passport and the biometric data.

Both ICAO and IATA have their own airport and airline code systems.

{{main article|ICAO airport code}}

ICAO uses 4-letter airport codes (vs. IATA's 3-letter codes). The ICAO code is based on the region and country of the airport—for example, Charles de Gaulle Airport has an ICAO code of LFPG, where L indicates Southern Europe, F, France, PG, Paris de Gaulle, while Orly Airport has the code LFPO (the 3rd letter sometimes refers to the particular flight information region (FIR) or the last two may be arbitrary). In most parts of the world, ICAO and IATA codes are unrelated; for example, Charles de Gaulle Airport has an IATA code of CDG. However, the location prefix for the continental United States is K, and ICAO codes are usually the IATA code with this prefix. For example, the ICAO code for Los Angeles International Airport is KLAX. Canada follows a similar pattern, where a prefix of C is usually added to an IATA code to create the ICAO code. For example, Calgary International Airport is YYC or CYYC. (In contrast, airports in Hawaii are in the Pacific region and so have ICAO codes that start with PH; Kona International Airport's code is PHKO. Similarly, airports in Alaska have ICAO codes that start with PA. Merrill Field, for instance is PAMR.) Not all airports are assigned codes in both systems; for example, airports that do not have airline service do not need an IATA code.

ICAO also assigns three-letter airline codes versus the more-familiar two-letter IATA codes—for example, UAL vs. UA for United Airlines. ICAO also provides telephony designators to aircraft operators worldwide, a one- or two-word designator used on the radio, usually, but not always, similar to the aircraft operator name. For example, the identifier for Japan Airlines International is JAL and the designator is Japan Air, but Aer Lingus is EIN and Shamrock. Thus, a Japan Airlines flight numbered 111 would be written as "JAL111" and pronounced "Japan Air One One One" on the radio, while a similarly numbered Aer Lingus would be written as "EIN111" and pronounced "Shamrock One One One". In the US, FAA practices{{cite web |url=https://www.faa.gov/air_traffic/publications/ATpubs/ATC/atc0204.html |title=Archived copy |access-date=2010-03-27 |url-status=dead |archive-url=https://web.archive.org/web/20100416174212/http://www.faa.gov/air_traffic/publications/atpubs/atc/atc0204.html |archive-date=16 April 2010}} require the digits of the flight number to be spoken in group format ("Japan Air One Eleven" in the above example) while individual digits are used for the aircraft tail number used for unscheduled civil flights.

{{main|List of aircraft registration prefixes}}

ICAO maintains the standards for aircraft registration, including the alphanumeric codes that identify the country of registration.

{{main|List of aircraft type designators}}

{{See also|Type rating}}

ICAO is also responsible for issuing two to four character alphanumeric aircraft type designators for those aircraft types which are most commonly provided with air traffic service. These codes provide an abbreviated aircraft type identification, typically used in flight plans. For example, the Boeing 747-100, -200 and -300 are given the type designators B741, B742 and B743 respectively.{{cite web |title=DOC 8643 – Aircraft Type Designators |url=https://www.icao.int/publications/doc8643/Pages/default.aspx |publisher=ICAO |access-date=1 February 2019 |ref=doc8643 |date=1 February 2019 |archive-url=https://web.archive.org/web/20190202042325/https://www.icao.int/publications/doc8643/Pages/default.aspx |archive-date=2 February 2019 |url-status=live }}

Since 2010, ICAO recommends a unification of units of measurement within aviation based on the International System of Units (SI), using:{{Cite web |url=https://www.icao.int/publications/Documents/9958_en.pdf |title=International Civil Aviation Organization - Assembly Resolutions in Force (as of 8 October 2010) - Doc 9958 - Published by authority of the Secretary General |access-date=26 October 2019 |archive-url=https://web.archive.org/web/20191210005805/https://www.icao.int/publications/Documents/9958_en.pdf |archive-date=10 December 2019 |url-status=live }}{{Cite web |url=https://aerosavvy.com/wp-content/uploads/2014/08/an05_cons.pdf |title=International Civil Aviation Organization - International Standards and Recommended Practices - Annex 5 to the Convention on International Civil Aviation - Units of Measurement to be Used in Air and Ground Operations Fifth Edition - July 2010 |access-date=26 October 2019 |archive-url=https://web.archive.org/web/20191210005804/https://aerosavvy.com/wp-content/uploads/2014/08/an05_cons.pdf |archive-date=10 December 2019 |url-status=live }}

• kilometres per hour (km/h) for speed during travel.
• metres per second (m/s) for wind speed during landing.
• kilometres (km) for distance.
• metres (m) for elevation.

Non-SI units have been permitted for temporary use since 1979,Council action in pursuance of Assembly Resolution A22-18 adopted 23 March 1979:

[..]to cover all aspects of air and ground operations; provision of standardized system of units based on the SI; identification of non-SI units permitted for use in international civil aviation; provision for termination of the use of certain non-SI units. but a termination date has not yet been established, which would complete metrication of worldwide aviation,{{Cite web |url=https://aerosavvy.com/metric-imperial/ |title=Aviation's Crazy, Mixed Up Units of Measure – AeroSavvy |access-date=26 October 2019 |archive-url=https://web.archive.org/web/20191207230641/http://aerosavvy.com/metric-imperial/ |archive-date=7 December 2019 |url-status=live |date=5 September 2014 }} and the following units are still in widespread use within commercial aviation:

• knots (kn or kt) for speed.
• nautical mile (NM) for distance.
• foot (ft) for elevation.

inches of mercury are used in Japan and North America to measure pressure, although sometimes METAR at Japanese airports show only hPa.

Aviation in Russia and China currently use km/h for reporting airspeed, and many present-day European glider planes also indicate airspeed in kilometres per hour.{{citation needed |date=October 2019}} China and North Korea use metres for reporting altitude when communicating with pilots. Russia also formerly used metres exclusively for reporting altitude, but in 2011 changed to feet for high altitude flight. From February 2017, Russian airspace started transitioning to reporting altitude in feet only. Runway lengths are now commonly given in metres worldwide, except in North America where feet are commonly used.

The following table summarizes units commonly used in flight and ground operations and their recommended replacement. A full list of recommended units can be found in annex 5 to the Convention on International Civil Aviation.

{{sup|†}} Altitude, elevation, height.

ICAO has a headquarters, seven regional offices, and one regional sub-office:{{cite web|title=Contact Us|url=http://www.icao.int/Pages/Contact_us.aspx|publisher=ICAO|access-date=2012-09-06|archive-url=https://web.archive.org/web/20130929221825/http://www.icao.int/Pages/contact_us.aspx|archive-date=29 September 2013|url-status=live}}

• Headquarters – Montreal, Quebec, Canada
• Asia and Pacific (APAC) – Bangkok, Thailand; Sub-office – Beijing, China
• Eastern and Southern African (ESAF) – Nairobi, Kenya
• Europe and North Atlantic (EUR/NAT) – Paris, France
• Middle East (MID) – Cairo, Egypt
• North American, Central American and Caribbean (NACC) – Mexico City, Mexico
• South American (SAM) – Lima, Peru
• Western and Central African (WACAF) – Dakar, Senegal

{{further|Environmental impact of aviation}}

{{Update|inaccurate=yes|section|date=February 2009}}

Emissions from international aviation are specifically excluded from the targets agreed under the Kyoto Protocol. Instead, the Protocol invites developed countries to pursue the limitation or reduction of emissions through the International Civil Aviation Organization. ICAO's environmental committee continues to consider the potential for using market-based measures such as trading and charging, but this work is unlikely to lead to global action. It is currently developing guidance for states who wish to include aviation in an emissions trading scheme (ETS) to meet their Kyoto commitments, and for airlines who wish to participate voluntarily in a trading scheme.{{citation needed|date=December 2020}}

Emissions from domestic aviation are included within the Kyoto targets agreed by countries. This has led to some national policies such as fuel and emission taxes for domestic air travel in the Netherlands and Norway, respectively. Although some countries tax the fuel used by domestic aviation, there is no duty on kerosene used on international flights.{{cite web|title=Climate Change: Aviation Emissions, an ignored but fast growing problem|url=http://www.aef.org.uk/downloads/Factsheetclimate.pdf|publisher=greenskies.org|access-date=3 August 2011|year=2005|archive-url=https://web.archive.org/web/20110716144742/http://www.aef.org.uk/downloads/Factsheetclimate.pdf|archive-date=16 July 2011|url-status=live}}

ICAO is currently opposed to the inclusion of aviation in the European Union Emission Trading Scheme (EU ETS). The EU, however, is pressing ahead with its plans to include aviation.{{citation needed|date=December 2020}}

ICAO has been called "flawed and biased in favour of the industry" by Jo Dardenne, the manager for aviation at Transport & Environment.[https://www.theguardian.com/environment/2021/jun/30/un-aviation-emissions-body-decried-for-hiring-industry-lobbyist UN aviation emissions body decried for hiring industry lobbyist] {{Webarchive|url=https://web.archive.org/web/20210705084240/https://www.theguardian.com/environment/2021/jun/30/un-aviation-emissions-body-decried-for-hiring-industry-lobbyist |date=5 July 2021 }} The Guardian, 2021

{{further|Carbon Offsetting and Reduction Scheme for International Aviation}}

On 6 October 2016, the ICAO finalized an agreement among its 191 member nations to address the more than {{val|1000|u= million tonnes}} of carbon dioxide emitted annually by international passenger and cargo flights. The agreement will use an offsetting scheme called CORSIA (the Carbon Offsetting and Reduction Scheme for International Aviation) under which forestry and other carbon-reducing activities are directly funded, amounting to about 2% of annual revenues for the sector. Rules against 'double counting' should ensure that existing forest protection efforts are not recycled. The scheme did not take effect until 2021 and will be voluntary until 2027, but many countries, including the US and China, have promised to begin at its 2020 inception date. Under the agreement, the global aviation emissions target is a 50% reduction by 2050 relative to 2005.{{cite web|last1=Gill|first1=Michael|title=Preparing for CORSIA Take-Off|url=http://www.ieta.org/resources/Resources/GHG_Report/2017/Preparing%20for%20CORSIA%20Take-off%20-%20Gill.pdf|website=IETA.org|access-date=19 September 2017|archive-url=https://web.archive.org/web/20170919234006/http://www.ieta.org/resources/Resources/GHG_Report/2017/Preparing%20for%20CORSIA%20Take-off%20-%20Gill.pdf|archive-date=19 September 2017|url-status=live}} NGO reaction to the deal was mixed.{{cite news |first= Oliver |last= Milman |title= First deal to curb aviation emissions agreed in landmark UN accord |date= 6 October 2016 |work= The Guardian |location= London, United Kingdom |url= https://www.theguardian.com/environment/2016/oct/06/aviation-emissions-agreement-united-nations |access-date= 22 October 2016 |archive-date= 20 October 2016 |archive-url= https://web.archive.org/web/20161020175045/https://www.theguardian.com/environment/2016/oct/06/aviation-emissions-agreement-united-nations |url-status= live }}{{cite news |author=Henry Fountain |title='Aviation's Paris Moment' as Nations Near Emissions Deal |url=https://www.nytimes.com/2016/09/26/business/energy-environment/aviations-paris-moment-as-nations-near-emissions-deal.html |archive-url=https://ghostarchive.org/archive/20220103/https://www.nytimes.com/2016/09/26/business/energy-environment/aviations-paris-moment-as-nations-near-emissions-deal.html |archive-date=2022-01-03 |url-access=subscription |url-status=live |newspaper=NYT |date=25 September 2016 }}{{cbignore}}{{cite news |author=Henry Fountain |title=Over 190 Countries Adopt Plan to Offset Air Travel Emissions |url=https://www.nytimes.com/2016/10/07/science/190-countries-adopt-plan-to-offset-jet-emissions.html |archive-url=https://ghostarchive.org/archive/20220103/https://www.nytimes.com/2016/10/07/science/190-countries-adopt-plan-to-offset-jet-emissions.html |archive-date=2022-01-03 |url-access=subscription |url-status=live |newspaper=NYT |date=6 October 2016}}{{cbignore}}

The agreement has critics. It is not aligned with the 2015 Paris climate agreement, which set the objective of restricting global warming to 1.5 to 2 °C. A late draft of the agreement would have required the air transport industry to assess its share of global carbon budgeting to meet that objective, but the text was removed in the agreed version.[http://www.climatechangenews.com/2016/10/06/un-aviation-pact-will-not-be-aligned-with-paris-climate-goals/ UN aviation pact will not be aligned with Paris climate goals] {{Webarchive|url=https://web.archive.org/web/20161021074547/http://www.climatechangenews.com/2016/10/06/un-aviation-pact-will-not-be-aligned-with-paris-climate-goals/ |date=21 October 2016 }}, M. Darby, Climate Change News, 6 October 2016.[http://theconversation.com/the-new-un-deal-on-aviation-emissions-leaves-much-to-be-desired-66768 The new UN deal on aviation emissions leaves much to be desired] {{Webarchive|url=https://web.archive.org/web/20171201031014/https://theconversation.com/the-new-un-deal-on-aviation-emissions-leaves-much-to-be-desired-66768 |date=1 December 2017 }}, D. Hodgkinson & R. Johnston. The Conversation, 10 October 2016. CORSIA will regulate only about 25 percent of aviation's international emissions, since it grandfathers all emissions below the 2020 level, allowing unregulated growth until then.[http://www.biologicaldiversity.org/news/press_releases/2016/airplane-emissions-10-06-2016.html Weak Market-based Measure Allows Airplanes' Greenhouse Pollution to Triple] {{Webarchive|url=https://web.archive.org/web/20161007183828/http://www.biologicaldiversity.org/news/press_releases/2016/airplane-emissions-10-06-2016.html |date=7 October 2016 }}, press release by Center for Biological Diversity and Friends of the Earth. 6 October 2016. Only 65 nations will participate in the initial voluntary period, not including significant emitters Russia, India and perhaps Brazil. The agreement does not cover domestic emissions, which are 40% of the global industry's overall emissions. One observer of the ICAO convention made this summary: {{Blockquote|Airline claims that flying will now be green are a myth. Taking a plane is the fastest and cheapest way to fry the planet and this deal won't reduce demand for jet fuel one drop. Instead offsetting aims to cut emissions in other industries,}} although another critic called it "a timid step in the right direction."[http://www.commondreams.org/news/2016/10/06/green-groups-warn-deal-lower-aviation-pollution-weak-shell-game Green Groups Warn Deal to Lower Aviation Pollution is 'Weak Shell Game'] {{Webarchive|url=https://web.archive.org/web/20161021072936/http://www.commondreams.org/news/2016/10/06/green-groups-warn-deal-lower-aviation-pollution-weak-shell-game |date=21 October 2016 }}, N. Prupis, Common Dreams, 6 October 2016

ICAO has expressed strong opposition to 2025 proposals from various UN bodies and international organizations, including the International Monetary Fund, suggesting new taxes or levies on international aviation to fund global climate initiatives. ICAO contends that such measures could undermine CORSIA, emphasizing that CORSIA is the sole global framework for addressing international aviation emissions and warning that additional levies could disrupt its implementation and the broader goal of sustainable aviation development. While acknowledging the need for increased climate finance, ICAO urged stakeholders to support existing mechanisms like CORSIA rather than introducing potentially conflicting financial measures. {{cite news |title= ICAO “deeply concerned” over proposals to raise global climate finance through international levies on aviation |url= https://www.greenairnews.com/?p=7169 |accessdate=1 May 2025 |agency=Green Air News |date=22 April 2025}}

Emissions limits for aircraft engines are defined by the Annex 16, Volume 2 of the ICAO Technology Standards, they include standards for hydrocarbons, carbon monoxide, NOx, smoke and particulate matter for local air quality near airports, below {{cvt|3,000|feet}}. The first ICAO emissions regulation was adopted in 1981, and more stringent NOx standards were subsequently adopted: CAEP/2 in 1993, CAEP/4 in 1999, CAEP/6 in 2005 and CAEP/8 in 2011. Higher bypass ratios, lean burn and Rich Quick Quench Lean combustor design can reduce NOx emissions.{{cite web |url= https://www.icao.int/Meetings/EnvironmentalWorkshops/Documents/2015-Warsaw/4_1_Local-Air-Quality-and-ICAO-Engine-Emissions-Standards.pdf |title= Local Air Quality and ICAO Engine Emissions Standards |author= Neil Dickson |work= Committee on Aviation Environment Protection |publisher= ICAO |date= 2015 |archive-url= https://web.archive.org/web/20210704071126/https://www.icao.int/Meetings/EnvironmentalWorkshops/Documents/2015-Warsaw/4_1_Local-Air-Quality-and-ICAO-Engine-Emissions-Standards.pdf |archive-date= 4 July 2021 |url-status= live }}

Most air accident investigations are carried out by an agency of a country that is associated in some way with the accident. For example, the Air Accidents Investigation Branch conducts accident investigations on behalf of the British Government. ICAO has conducted four investigations involving air disasters, of which two were passenger airliners shot down while in international flight over hostile territory.

1. Libyan Arab Airlines Flight 114 which was shot down on 21 February 1973 by Israeli F-4 jets over the Sinai Peninsula during a period of tension that led to the Arab-Israeli Yom Kippur War killing 108 people.
2. Korean Air Lines Flight 007, which was shot down on 1 September 1983 by a Soviet Su-15 interceptor near Moneron Island just west of Sakhalin Island during a period of heightened Cold War tension killing all 269 people on board including U.S. Representative Larry McDonald.{{cite book |title=KAL 007: Cover-up |author=David Pearson |publisher=Summit Books |location=New York |year=1987 |page=[https://archive.org/details/kal007coverup00pear/page/266 266] |url=https://archive.org/details/kal007coverup00pear |url-access=registration |isbn=978-0-671-55716-4}}
3. UTA Flight 772, which was destroyed by a bomb on 19 September 1989 above the Sahara Desert in Niger, en route from N'Djamena, Chad, to Paris, France. The explosion caused the aircraft to break up, killing all 156 passengers and 15 crew members, including the wife of U.S. Ambassador Robert L. Pugh. Investigators determined that a bomb placed in the cargo hold by Chadian rebels backed by Libya was responsible for the explosion. A French court convicted in absentia six Libyans of planning and implementing the attack.{{cite web|url=http://aviation-safety.net/database/record.php?id=19890919-1|title=ASN Aircraft accident McDonnell Douglas DC-10-30 N54629 Ténéré desert|first=Harro|last=Ranter|website=aviation-safety.net|access-date=31 May 2017|archive-url=https://web.archive.org/web/20111209181930/http://aviation-safety.net/database/record.php?id=19890919-1|archive-date=9 December 2011|url-status=live}}
4. The 1996 shootdown of Brothers to the Rescue aircraft on 24 February 1996, when two civilian aircraft operating north of Cuba were shot down by two jets of the Cuban Air Force. The Cuban military alleged that aircraft operated by the group Brothers to the Rescue had scattered propaganda leaflets onto Cuba prior to the incident, and issued orders that such aircraft be shot down. All four crew members aboard the two aircraft were killed, whilst a third aircraft managed to escape and return to the American mainland.

ICAO is looking at having a singular ledger for drone registration to help law enforcement globally. Currently, ICAO is responsible for creating drone regulations across the globe, and it is expected that it will only maintain the registry. This activity is seen as a forerunner to global regulations on flying drones under the auspices of the ICAO.{{Cite news|url=https://www.geospatialworld.net/blogs/un-proposes-setting-up-a-global-database-for-drone-registration/|title=UN proposes global database for drone registration|date=2017-10-06|work=Geospatial World|access-date=2017-10-06|language=en-US|archive-url=https://web.archive.org/web/20171007115832/https://www.geospatialworld.net/blogs/un-proposes-setting-up-a-global-database-for-drone-registration/|archive-date=7 October 2017|url-status=live}}

ICAO currently maintains the 'UAS Regulation Portal'{{Cite web|url=https://www.icao.int/safety/RPAS/Pages/UAS-Regulation-Portal-COM.aspx|title=UAS Regulation Portal|website=icao.int|language=en-us|access-date=2017-10-06|archive-url=https://web.archive.org/web/20171007021404/https://www.icao.int/safety/RPAS/Pages/UAS-Regulation-Portal-COM.aspx|archive-date=7 October 2017|url-status=dead}} for various countries to list their country's UAS regulations and also review the best practices from across the globe.

• Airline codes (includes ICAO codes)
• {{lang|fr|Fédération Aéronautique Internationale|italic=no}} (FAI)
• Freedoms of the air
• ICAO airport code
• International Maritime Organization
• Kenneth Macdonald Beaumont
• List of aircraft manufacturers by ICAO name
• International Aviation Services Organization{{cite web|url=https://mixjet.aero/blog/the-story-of-the-international-aviation-services-organization-iaso/|title=recognition of IASO by ICAO|date=30 March 2020 |access-date=March 16, 2024|archive-date=16 March 2024|archive-url=https://web.archive.org/web/20240316192319/https://mixjet.aero/blog/the-story-of-the-international-aviation-services-organization-iaso/|url-status=live}}

{{reflist|30em}}

{{Library resources box}}

• [http://www.icao.int/ Official website of the International Civil Aviation Organization]
• [http://www.icao.int/publications/Pages/doc7300.aspx Convention on International Civil Aviation – Document 7300]
• [http://www.icao.int/safety/ism/Accident%20Incident%20Reporting%20Guidance/LocationIndicatorsByState.pdf ECCAIRS 4.2.8 Data Definition Standard – Location Indicators by State, 17 Sep 2010] {{Webarchive|url=https://web.archive.org/web/20190325001252/https://www.icao.int/safety/ism/Accident%2520Incident%2520Reporting%2520Guidance/LocationIndicatorsByState.pdf |date=25 March 2019 }}
• [http://www.icao.int/publications/DOC8643/Pages/Doc8643.aspx ICAO Aircraft and Manufacturer Codes – Document 8643]
• [https://applications.icao.int/postalhistory/ The Postal History of the International Civil Aviation Organization (ICAO)]
• [https://international.thenewslens.com/article/50372 ICAO Will Mute Mics At Mention of Taiwan: Paraguay Official]

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