Overdrive
The meaning of Red and Green generally is entrenched. But this is aviation and we are professionals. Rules change all the time. I can tell you that to research and justify to ICAO a CAD based colour vision test that is not going to fix the problem and will be very expensive. The fact that the Papi is red and white is an example that we are adaptable, easy just change the rules and send a letter to every pilot, done. The light signals are used so often that most pilots have forgotten what they mean and the lamps in the towers are covered with dust.
If they were serious about red and green the Papi system would have been designed to show 4 greens when "on-slope". But the designers knew that green and red are easily mixed up even for colour normal’s under some conditions and therefore the approach would not be fool-proof, which it isn’t anyway. They have designed the Papi to show both colours together so that you can see which is which even in dusty conditions and this reduces the risk of a mix up. If you see all one colour then you better check the radalt because you screwed it up before you got to the Papi. Remember the Papi is for within 5nm unless you've got an ILS (7nm).
Better still get rid of the Papi and stick with the Vasi, it's a far better system, more expensive but very reliable and does not discriminate. I see we provide wheel chair access to toilets for those who cannot walk and subsidise dogs for those who cannot see, why not make the workplace colour vision friendly?
