Just briefly returning to airways fan markers, I only started airways flying at the time they had become pretty rare, say the mid-eighties; it used to happen from time to time that the marker receiver was left on audio by mistake, and we would be flying along, thumb in bum, mind in neutral, doing the crossword or chatting up a hosty when suddenly there would be a yellow flashing light and an insistent "beep-beep-beep-beep".
Used to grab the attention fairly effectively!
Are there any left, does anyone know?
W