when passing the threshold, the typical altitude is 50ft, which is the GS height over the threshold. the aircraft GS antenna is locate near the nose, so when passing the threshold, the cockpit is around 50ft, and the GPWS anounces RA50, according to the FCTM, the landing gear is around 35ft height.
and when decend and flare, the RA and landing gear decrease syncronized to 0.
I heard that there is a program pin in there for calculation for the aircraft pitch, bank angle, antenna location etc. for landing.
does someone know this program?