Originally Posted by extricate
Am I missing something?
Yes you are. Every "long" runway in Oz, ie those which might accept "long" or "high" bodies jets, has a MEHT of at least 60ft. The MEHT, of course relates only to the PAPI. The Glideslope threshold crossing height is a different kettle of fish altogether and is always 50ft.
The difference exists because, if the MEHT (for the PAPI) was 50ft, when the jet was on the GS, you'd see 4 whites out of your long/high body. Looking at it from another angle, if you did a visual approach without the GS, if you had a MEHT of 50ft and followed it, the wheels of your long/high jet would be
very low over the threshold.
What this all means is that, when on the ILS GS, the PAPI will look basically OK (2W2R) when you're on short final. If you are in a tiddler, then, at the DA, you'll probably see 3R because your eyes and the GS are closer together.
A further clue is the physical location of the PAPI. It will be on the front edge of the aiming point marking, which, on a longer runway, is well past the 300m marker (which is where the GS touches the ground).