VASI / PAPI
There is a certain error induced if the VASI or the PAPI is followed all the way to touchdown.. .Visual guidance systems like the PAPI are designed for a certain fuselage length and unlike the old VASI, there is no different view for a long body type.. .Even on the most pefect approach, say an Autoland, there is a stage when the PAPI turns 'All Red' on a smaller aircraft, and almost 'All White' on a very long airplane.. .Can somebody throw light on the subject, especially on the height at which they cease to be reliable, and where is the information to be found?