Annex 10 - Aeronautical Telecommunications


Annex 10

Developed by ICAO, the International Standards and Recommended Practices (SARPS) contained in the eighteen 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:

- Volume I: Radio Navigation Aids.

- Volume II: Communication Procedures.

- Volume III: Digital Data Communication Systems and Voice Communications Systems.

- Volume IV: Surveillance Radar and Collision Avoidance Systems

- Volume V: Aeronautical Radio Frequency Spectrum Utilization.


International Radiotelephony

Spelling Alphabet

It is interesting to note that the first internationally recognized phonetic alphabet was adopted by the International Telecommunications Union (ITU)  Radio Conference in 1927 and was for use by the maritime mobile service; such alphabet assigns code words to each letter of the alphabet (i.e. Alfa for A, Bravo for B, etc.), 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. The experience gained with that alphabet resulted in several changes being made by the 1932 Radio Conference of ITU. 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.


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, it was recognized that 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.


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. During 1948 and 1949, Professor Jean-Paul Vinay of the University of Montreal, 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.


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. 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 here on the left-side (and printed in Annex 10, volume II) 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.


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 any one 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, 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.



First Day Cover - Special Middle East Communications Meeting

Rhodes, Greece - 11 to 31 May 1954

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.






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.