Being on the same page is key in controlling. In Infinite Flight we have the luxury of using text-to-speech. It’s a luxury because not everyone speaks English fluently, and in the real world dialects have to be taken into account. That is why you hear “niner” or “tree” instead of “nine” or “three.
The pronunciation of the digits 3, 4, 5, and 9 differs from standard English – being pronounced tree, fower, fife, and niner. The digit 3 is specified as tree so that it is not pronounced sri; the long pronunciation of 4 (still found in some English dialects) keeps it somewhat distinct from for; 5 is pronounced with a second “f” because the normal pronunciation with a “v” is easily confused with “fire” (a command to shoot); and 9 has an extra syllable to keep it distinct from German nein ‘no’.
The phonetic alphabet is not a random selection of words.
The final choice of code words for the letters of the alphabet and for the digits was made after hundreds of thousands of comprehension tests involving 31 nationalities.