Annex 10 - Aeronautical Telecommunications


Annex 10

Developed by ICAO, the International Standards and Recommended Practices (SARPS) contained in the nineteen Technical Annexes to the Convention on International Civil Aviation (also called Chicago Convention) are applied universally and produce a high degree of technical uniformity which has enabled international civil aviation to develop in a safe, orderly and efficient manner. Among those Annexes, Annex 10 Aeronautical Telecommunications covers three of the most complex and essential elements of international civil aviation. i.e., aeronautical communications, navigation and surveillance. Annex 10 is divided into five volumes:

1.    Volume I - Radio Navigation Aids

2.    Volume II - Communications Procedures including those with PANS status

3.    Volume III - Communication Systems
     a. Part 1 - Digital Data Communication Systems
     b. Part 2 - Voice Communication Systems

4.    Volume IV - Surveillance Radar and Collision Avoidance Systems

5.    Volume V - Aeronautical Radio Frequency Spectrum Utilization

6.    Volume VI – Communication Systems and Procedures to Remotely Piloted Aircraft Systems C2 Link.


Standards and Recommended Practices for Aeronautical Telecommunications were first adopted by the Council on 30 May 1949 and designated as Annex 10 to the Chicago Convention; they became effective on 1 March 1950. These Standards and Recommended Practices were based on recommendations of the Communications Division at its Third Session from 11 January to 26 February 1949.


Up to and including the Seventh Edition, Annex 10 was published in one volume containing four Parts together with associated attachments: Part I - Equipment and Systems, Part II - Radio Frequencies, Part III - Procedures, and Part IV - Codes and Abbreviations. By Amendment 42 adopted on 25 March 1964, Part IV was deleted from the Annex; the codes and abbreviations contained in that Part were transferred to a new ICAO document, Doc 8400. As a result of the adoption of Amendment 44 on 31 May 1965, the Seventh Edition of Annex 10 was replaced by two volumes: Volume I containing Part I - Equipment and Systems, and Part II - Radio Frequencies, and Volume II containing Communication Procedures. Further to the work of Third Meeting of the Aeronautical Mobile Communications Panel (AMCP, held in Montréal from 7 to 22 April 1994) and as a result of the adoption of Amendment 70 on 20 March 1995, Annex 10 was restructured to include five volumes as known today; in addition to Standards and Recommended Practices (SARPs), the five volumes of this Annex 10 contain Procedures for Air Navigation Services (PANS) and guidance material on aeronautical communication, navigation and surveillance systems.


An important element of the ground-ground communication is the Aeronautical Fixed Telecommunications Network (AFTN), a worldwide network organized to meet the specific requirements of international civil aviation. This is an integrated system of aeronautical fixed circuits provided as part of the Aeronautical Fixed Service (AFS) for the exchange of communication and/or digital data between the aeronautical stations having the same or compatible communications characteristics. Within the AFTN category, all significant ground points, which include airports, air traffic control centres, meteorological offices and the like, are joined by appropriate links designed to serve aircraft throughout all phases of flight. Messages originated at any point on the network are routed as a matter of routine to all points required for the safe conduct of flight. The AFTN exchanges vital information for aircraft operations such as distress messages, urgency messages, flight safety messages, meteorological messages, flight regularity messages and aeronautical administrative messages. The format of AFTN messages is defined in ICAO Annex 10, Volume II.


ICAO Spelling Alphabet


International Radiotelephony

Spelling Alpha bet

When a pilot is communicating with air traffic control, static and other interferences would often create confusion with specific English language letters. In the very early days of civil aviation and military communication, and even today when dealing with businesses over the phone, a universal spelling alphabet is used to clarify parts of messages that contain letters and numbers. With short and simple words, ICAO’s phonetic alphabet lowers the chance of misunderstandings and increases operational safety for passengers and crew.


A spelling or phonetic alphabet assigns code words to each letter of the alphabet, so that critical combinations of letters (and numbers) can be pronounced and understood by those who transmit and receive voice messages by radio or telephone regardless of their native language, especially when the safety of navigation or persons is essential. Each word in a spelling alphabet typically replaces the name of the letter with which it starts (acrophony).


It is interesting to note that the first non-military internationally recognized spelling (phonetic) alphabet was adopted by the International Telecommunications Union (ITU) Radio Conference held in Washington in 1927 at Washington and was for use by the maritime mobile service.

Note that 1) the C.C.I.R. (Consultative Committee on International Radiocommunication) was set up by Article 17 of the International Radiotelegraph Convention concluded at Washington on 25 November 1927; 2) the CCIR and several other organizations merged to form what would become known in 1934 as the International Telecommunication Union; in 1992, the CCIR became the ITU-R, the ITU Radiocommunication Sector, i.e., one of the three sectors of the ITU.


The experience gained with that alphabet resulted in several changes being made by the 1932 Radio Conference of ITU held in Madrid. The resulting alphabet was adopted by the International Commission for Air Navigation (ICAN), the predecessor of ICAO, and was used in civil aviation until World War II (ICAN Alphabet: Amsterdam Baltimore Casablanca Danemark Edison Florida Gallipoli Havana Italia Jerusalem Kilogramme Liverpool Madagascar New_York Oslo Paris Quebec Roma Santiago Tripoli Upsala Valencia Washington Xanthippe Yokohama Zurich).


During WWII, the military requirements of joint operations let to the development of a common spelling alphabet for the use of the combined allied services; it became known as the Able Baker alphabet after the words for the letters A and B. After World War II, with many aircraft and ground personnel drawn from the allied armed forces, the "Able/Baker" alphabet continued to be used in civil aviation. The Second Session of the ICAO Communications Division naturally adopted in 1946 that alphabet. However civil aviation begun to suffer confusion in South America where English words were not fully recognized; many speech sounds of this alphabet were associated only with the English language; in fact, an alternative alphabet "Ana/Brazil" was approved by ICAO and introduced for the South American and Caribbean regions.


Able/Baker Alphabet: Able Baker Charlie Dog Easy Fox George How Item Jig King Love Mike Nan Oboe Peter Queen Roger Sugar Tare Uncle Victor William X-ray Yoke Zebra.


Ana/Brazil Alphabet: Ana Brazil Coco Dado Elsa Fiesta Gato Hombre India Julio Kilo Luis Mama Norma Opera Peru Quebec Rosa Sara Tomas Uruguay Victor Whiskey Equis Yolanda Zeta


At the International Radio Conference held in Atlantic City in 1947, it was decided that the International Civil Aviation Organization and other international aeronautical organizations would assume the responsibility for procedures and regulations related to aeronautical communication. However, ITU would continue to maintain general procedures regarding distress signals.


The coexistence of two spelling alphabets led IATA at its First Technical Conference in Nice in 1947 to submit for consideration by ICAO a first draft of a proposed single universal alphabet that had sounds common to English, French, Spanish and Portuguese.


During 1948 and 1949, Professor Jean-Paul Vinay of the Université de Montréal, Canada worked on the problem in collaboration with the ICAO Language Section. After those studies, consultations with communications experts and comments from all of ICAO’s member governments, a new ICAO alphabet was adopted and incorporated in the Aeronautical Telecommunications Annex 10 for implementation on 1 November 1951 in civil aviation, with one-year transition to this new alphabet: Alfa Bravo Coca Delta Echo Foxtrot Golf Hotel India Juliett Kilo Lima Metro Nectar Oscar Papa Quebec Romeo Sierra Tango Union Victor Whisky Extra Yankee Zulu.


The new spelling alphabet was based on the following criteria:

1.     A world could only be considered if it was a live word in each of the three working languages and had a similar spelling in English, French, and Spanish;

2.     It had to be easily pronounced and recognized by airmen of all languages, clearly transmissible by radio and easy to read;

3.     A chosen word could not have any negative meaning or association.


Jean-Paul Vinay (1910-1999) was one of the foremost Linguists and Researchers from Canada who has deeply influenced teaching of second languages, translation, and language discipline in Canada and abroad; in 1950, he founded the department of linguistics at the Université de Montréal, where he set up the linguistics program as well as courses in translation and interpretation.


See related article by L.J. Rose here below.

The revised alphabet was eventually adopted on 1 November 1951 as a universal standard for communicating English letters over a phone or radio; it came into use for civil aviation on 1 April 1952, but it may not have been adopted by any military.


Immediately, problems were found with the newly adopted alphabet. Some users felt that they were so severe that they reverted to the old "Able/Baker" alphabet. Because of the complaints, ICAO decided in 1952 to re-examine the question and its member governments (through airlines, pilots, air traffic controllers, etc.) were invited to collaborate in further studies and actual tests which could be as objective as possible; testing was conducted among speakers from 31 countries, principally by the governments of Canada, the United Kingdom and the United States. The conclusions confirmed strikingly the basic soundness of the original work. However, confusion among words like Delta, Nectar, Victor, and Extra, or the unintelligibility of other words under poor receiving conditions were the main problems.


After much study, only the five words, i.e., Charlie, Mike, November, Uniform and X-Ray, representing the letters C, M, N, U, and X were replaced in the original alphabet. The final version given in the table shown on the left side (and printed in Annex 10, volume II, Chapter 5 - Aeronautical Mobile Service – Voice Communications) was implemented by ICAO on 1 March 1956, and thus was adopted by many other international and national organizations, including the North Atlantic Treaty Organization (NATO), ITU, the International Maritime Organization (IMO), etc. The phonetic alphabet became to be formally known as the International Radiotelephony Spelling Alphabet or the NATO Phonetic Alphabet. It is commonly referred to as the Alpha/Bravo/Charlie alphabet.


The pronunciation of the words in the alphabet may vary according to the language habits of the speakers; the approximate pronunciation is provided in Volume II of Annex 10. However, in order to eliminate wide variations in pronunciation, posters illustrating the desired pronunciation are available from ICAO. According to the 4-page ICAO pamphlet (see sample below) accompanying the recording illustrating the correct way of pronouncing the words of the new Radiotelephony Spelling Alphabet, distributed to all countries in November 1955 when the alphabet was introduced, the spelling alphabet was developed as a result of extensive studies involving hundreds of thousands of tests and the participation of both scientific personnel and those having extensive experience in aviation. Tests were conducted both between aircraft and aeronautical stations and under controlled laboratory conditions and the results obtained had shown a strong similarity.


In the official version of the alphabet, the non-English spellings Alfa and Juliett are used. Alfa is spelled with an f as it is in most European languages because the English and French spelling alpha would not be pronounced properly by native speakers of some other languages – who may not know that ph should be pronounced as f. Juliett is spelled with a tt for French speakers, because they may otherwise treat a single final ‘t’ as silent. In some English versions of the alphabet, one or both of these may have their standard English spelling.


According to Annex 10, volume II, Chapter 5, all numbers used in the transmission of altitude, cloud height, visibility and runway visual range (RVR) information, which contain whole hundreds and whole thousands, shall be transmitted by pronouncing each digit in the number of hundreds or thousands followed by the word HUNDRED or THOUSAND as appropriate. Combinations of thousands and whole hundreds shall be transmitted by pronouncing each digit in the number of thousands followed by the word THOUSAND followed by the number of hundreds followed by the word HUNDRED. When the language used for communication is English, numbers shall be transmitted using the pronunciation shown here at the left side. A few of them are pronounced differently from their standard English pronunciation; those include the number three, pronounced as tree (tri), five as fife and nine as niner.


According to Annex 10, Volume II, Chapter 5, the air-ground radiotelephony communications shall be conducted in the language normally used by the station on the ground or in the English language. The English language shall be available, on request from any aircraft station, at all stations on the ground serving designated airports and routes used by international air services. When proper names, service abbreviations and words of which the spelling is doubtful are spelled out in radiotelephony, the International Radiotelephony Spelling Alphabet is used. In most instances, all numbers shall be transmitted by pronouncing each digit separately.


This chapter on Annex 10 was translated into Italian by Nico Michelini; he added many references to the NATO documents concerning the adoption of the phonetic alphabet. See at the following links: L’alfabeto Fonetico Internazionale and Aviation’s ABC.


One important aspect of Aeronautical Communications is the use of Global Navigation Satellite System (GNSS) navigation in civil aviation. ICAO’s standardization of GNSS played a crucial role in enabling the use of GNSS by international civil aviation. In 1991, the 10th Air Navigation Conference requested the initiation of an agreement between ICAO and GNSS-provider States concerning quality and duration of GNS. The ICAO GNSS Panel was established in 1993.


The ICAO Council adopted the first ICAO GNSS Standards, contained in Annex 10 and applicable in March 2001, covering both Global Positioning System (GPS, operated by the United States) and GLObal NAvigation Satellite System (GLONASS, operated by the Russian Federation). ICAO officially endorsed GNSS as one of standard radio navigation aids, in addition to traditional aids such as instrument landing systems (ILS), very high frequency (VHF), VHF omnidirectional range (VOR), and distance measuring equipment (DME).


On the institutional side, both the United States and the Russian Federation took the unprecedented initiative of offering to the ICAO Council their respective GNSS systems, GPS and GLONASS respectively, to be available for international civil aviation. As regards the technical side, the ICAO GNSS Panel had to assess the extent to which GPS and GLONASS were able to meet safety requirements, and the technical means needed to be devised to augment their performance as required to meet those requirements in full.


Two decades after the ICAO Council adopted the GNSS SARPs, GNSS has been globally embraced by aviation users throughout the international and domestic air transport fleet and general aviation and constitutes the foundation of the ICAO Performance-Based Navigation (PBN) concept, by providing a ubiquitous navigation capability virtually regardless of ground infrastructure.


GNSS technology is evolving and offers today new opportunities to civil aviation. ICAO has accompanied its development since the inception of its deployment for civil aviation and will continue to do as GNSS evolves towards ever more advanced and robust navigation performance.


The first edition of the new Volume VI on “Communication Systems and Procedures to Remotely Piloted Aircraft Systems C2 Link” was dated July 2021.


In March 2023, the ICAO Council achieved a major milestone this week in the global standardization and roll-out of new dual-frequency multi-constellation (DFMC) capabilities for international aviation’s Global Navigation Satellite System (GNSS). “This is an important development toward improving the safety, efficiency and sustainability of international air transport through more precise airspace management and more efficient routes and procedures,” emphasized Council President Salvatore Sciacchitano. “Eventually these new standards will provide international aviation with access to an extensive global infrastructure and over 50 new GNSS satellites.” DFMC GNSS permits the combined leveraging of dual frequency signals from up to four GNSS constellations simultaneously, including the GPS system (United States), Galileo (European Union), GLONASS (Russian Federation), and BeiDou (China). The capability has been enabled through latest advances in aircraft-, satellite-, and ground-based augmentation systems, and will become more prevalent as aircraft become increasingly equipped with DMFC-capable avionics. Currently, global aviation GNSS capabilities rely mainly on just one constellation and one frequency via GPS L1, meaning that the new multi-constellation capability will assure greater system accuracy and redundancy, delivering important air network capacity and safety benefits. “ICAO has worked in close cooperation with EUROCAE and the RTCA on the development of these new standards, to ensure that they fully align with industry specifications,” commented ICAO Secretary General Juan Carlos Salazar.



First Day Cover - Special Middle East Communications Meeting.

Rhodes, Greece - 11 to 31 May 1954. Violet cancels.

This Meeting was called to consider among other items for the region: 1) proposals to amend the interim and final aeronautical fixed telecommunications network (AFTN) plans in the light of changing operational requirements; 2) proposals to amend the operational requirements for radio navigation aids in the light of recent developments in air operations; 3) review of progress of implementation of the regional plan for very high frequency communications in the aeronautical mobile service.


First Day Cover - Special Middle East Communications Meeting.

Rhodes, Greece – Cancel in blue dated 15 May 1954.


Canada – 1 June 1955 – First Day Cover

10th Anniversary of the interim Agreement and first PICAO Meeting

Picture representative of a Communications Service, showing a Monitor Control Unit which provides facilities for an instructor to monitor any selected or all operating circuits in the complete trainer; a tape recorder either records anyone selected circuit or may inject any prefabricated instructional material into any selected or all circuits in the system. The Monitor Control Unit was part of a Synthetic Air Traffic Communications Trainer, displayed at ICAO headquarters during the Personnel Licensing Division (held from 22 January to 14 February 1952) and designed by the US Civil Aeronautics Administration and ICAO; it could be shipped to any section of the world where ICAO training assistance teams (within the framework of the UN Expanded Programme for Technical Assistance) would train local personnel in the operation of modern aerodrome equipment.




Except from the ICAO Bulletin.






ICAO Phonograph recording (with the 4-page accompanying pamphlet) illustrating the correct way of pronouncing the words of the new Radiotelephony Spelling Alphabet, distributed to all countries in November 1955 when the alphabet was introduced.



Art Cartoons - 1956 ICAO Alphabet by Artist Carl Rose.

Creator/Publisher: Popular Science - March 1956 Edition, pages 160 and 161.

Approximate Size (inches): 6 x 9.

This is an original two-page two-colour print article about the airmen's alphabet for pilots that was developed by ICAO and illustrated through a series of cartoons by Artist Carl Rose.

Carl Rose (1903 – 1971) was an American cartoonist whose work appeared in The New Yorker, Popular Science, The Saturday Evening Post, and elsewhere.


ICAO Spelling Alphabet with pictograms associated to each letter.

Note two errors: 1) The letter “L” must be associated to the codeword Lima; 2) The letter “M” must be associated with the codeword Mike. Apparently, an adaptation from the original ICAO phonetic alphabet was made to assist visual recognition for these two letters!


Vintage Spark Plug Aircraft ICAO Alphabet Sticker.

Note the error in the name of the Organization: “Aeronautics” should have been “Aviation”.