Many years ago I frequently worked an aircraft with the callsign KKK. Brilliant pilot who, unfortunately for at least one other jockey, had a pronounced stutter which came up only on first contact.

".........., this is KKK". Took around 40 seconds. In the meantime the other hoop tried his rather necessary "Mayday, Mayday, Mayday...................." - to no avail. It took some considerable time to find out where the poor sod had crashed. The crashee survived.

Far as I remember he was checked out frequently but never stuttered once - but he always managed to do it on first contact on no-check days.