Originally Posted by
peekay4
For this specific runway (LGA RWY 4), two-dots high on the GS is not four whites on the PAPI, due the GS and PAPI not being coincident, as discussed in the previous page. (And why the FO is slow to correct).
In fact at the runway threshold, even a full-UP deflection on the ILS GS would be well
below the normal PAPI glide path!
We can calculate that for this runway, a full-up ILS GS deflection (3.8 degrees) at the threshold is 66 ft AGL, well below the PAPI TCH -- three reds! -- and just 3 ft above four-reds (at 63 ft).
A pilot flying the ILS right on the GS would see four-reds on the PAPI just prior to touchdown:
https://www.youtube.com/watch?v=VynLpoKXfxA
Yet the only warning on the approach plates is:
"VGSI and RNAV glidepath not coincident (VGSI Angle 3.10/TCH 76.)"
Surely, an approach where there is a gross difference between VGSI and ILS/RNP approaches should be highlighted a little more than a throw away comment? Perhaps:
"
WARNING - DISPLACED VISUAL THRESHOLD -
Glidepath on ILS will be shown 4 Reds by PAPI -
2 Red 2 White on PAPI will show as well above glidepath on ILS"
This would alert the crews to brief the PM prior to TOD that a panic reaction is NOT required if there is a mismatch ILS to VGSI