Originally Posted by
Ascend Charlie
Is the real reason for this rule simply that somebody with CVD could not distinguish between a green light and a red light shone from a tower? Something which I have only ever seen once, and that was because I asked the tower to shine it at me for a check?
The real reason for the original rule is that the rules of the air came from the rules of the sea, and navigation by sea required - and still requires - a deck officer to be able to identify colours. That is because, in sea navigation, the colour of a navaid is often itself essential information.
That is no longer the case in a contemporary civil aircraft operations.
But pilot CVD has been such a noble cause for some safety zealots for such a long time that it’s difficult to wean them off it. They know - just ask them - how crucial it is for HCRPT aircraft to achieve separation through the identification and interpretation of the Nav lights on other aircraft. They also know - just ask them - that one day the only thing stopping an aviation catastrophe will be a signal light gun in a control tower, and the CVD pilot who can’t understand the signals (as well as being inexplicably unable to see what’s happening on the runways and their approaches despite being able to see the tower...) will cause the catastrophe.