Foxmoth has it for the original question.
The answer to the supplementary is that the first person of royal blood to use a radio in an aircraft (Lord Bending, the third Earl of all saints) had a slight speech impediment. All loyal subjects (with the exception of the colonies) follow the lead of our aristocracy, hence the redundant "s". This is particularly present in the military who are frequently known to even call "initials" before "finals".
HTH to complete your day
HFD