Assymetricdrift,
Going into somewhere like Gatwick, if you follow the papi indication on the way down, you will find that your glide slope indication goes far too high. If you follow the ILS indication below minima you'll see that at 150 feet or so, you hit 3 red lights.
What is the TCH for the ILS and the MEHT for the PAPI? This will probably explain what you see.
Now, my question would be if you were doing a Cat II/Cat III landing, and with the autopilot disconnected at MUH, what the indication on the PAPIs would be? We did a practice Cat II into an airport recently, and when we came out of the simulated approach at 100 feet RH, the PAPIs were showing 3 red and 1 white.
From a
previous thread on this issue, the Canadians switch off the PAPI during low vis ops so this phenomenon doesn't occur. If you're on-slope on the ILS at 100ft, doing 10ft/sec, you must be pointed at the correct aim point and unless you do something crazy with the flight path you're going to "hit" the runway at the right point. What the PAPI shows is irrelevant.