18.104.22.168 Word spelling in radiotelephony. When proper names, service abbreviations and words of which the spelling is doubtful are spelled out in radiotelephony the alphabet in Figure 5-1 (The Radiotelephony Spelling Alphabet) shall be used.
Note 1. The pronunciation of the words in the alphabet as well as numbers may vary according to the language habits of the speakers. In order to eliminate wide variations in pronunciation, posters illustrating the desired pronunciation are available from ICAO.
Note 2. The Spelling Alphabet specified in 22.214.171.124 is also prescribed for use in the Maritime Mobile Service (ITU Radio Regulations, Appendix S14).
Source: ICAO Annex 10.2