which is the difference between a 3 degree PAPI and a 3 degree VASI??
PAPIs are a set of 4 lights mounted either side of the instrument TD point. Both pairs should be identical. For each set, too low and you get 4 red lights. As you get progressively stepper you will go through: 3 red, one white; 2 of each; one red, 3 white; 4 white. Two of each usually being 3 deg.
VASIs are separate bars of lights (like multiple PAPIs) but each bar is always all red or all white. Glideslope info comes from the progressive change of colour of the bars. I'll try to find some pictures.
Ahh! Found some of PAPIs
And some VASIs.
