"Either you are suggesting the a/c was descending at 'way outside' 20 000 fpm, or you don't understand the notion of radalt 'tracking capability'.
I assume the latter."
If you are claiming the tracking capability is based on terrain closure, ie, in the vertical, when flying at 330 fps and level, anything with a rise in terrain of 45 deg slope will out run the tracking capability. This includes buldings which have 90 degree "slopes".
The faster you go, the less slope in terrain that will be required to outrun the tracking capability.
Again, it is all explained here.
Aal77 Fdr Decoder Program - Pilots For 9/11 Truth Forum
You don't have to be descending for terrain to rise to you. The speed at which terrain rises to your altitude is a function of your forward speed.
The tracking capability is based on forward motion of the aircraft. These radalt's are used for low and slow approaches. They are not TFR radalts as used by Fighter and Attack aircraft following terrain.
As for pressure altimeters, which comment in particular are you referring to? That they are required for IFR flight and a radlat is not? Do you feel the static system in a standard 757 is not calibrated to .86 mach?