Originally Posted by FD
where the big rectangle is painted unnecessarily far down, to allow for the very large planes
I wouldn't call it "unnecessarily". The aim is to stop long-bodies touching down too close to the threshold. "Tiddlers" on that same runway (by definition, >2400m) will still have plenty of strip to land on, even if they do use the PAPI. The whole point of having a big white square is to use that as the visual aim point. If it was always at 300m in your long/big jet, you'd have to do trick flying to aim for ~400m so you didn't run the risk of scraping the mains through the grass if you got a tad low. ICAO has obviously decided that having a big white square in a realistic position is good. The Yanks, not (at least not on KLAX 07R).
Originally Posted by FD
In the US, the distance marker stays at 305 m (=1000') but PAPI can still be further down to accommodate the 747 and assure MLG clearance.
This post by Dan Winterland is informative:
747 aiming point - Following G/S or VASI's
With the gear down in the 747, the pilots eyes would definitely be heading somewhere in the vicinity of your 440m, way down the runway compared to the GS path.
Originally Posted by FD
My charts shows GP at THR of 60', meaning the signal is aligned to an imaginary distance of 1144 ft = 349 m past the threshold.
You mean "TCH" (as opposed to MEHT).