skwinty,
The pressure data in the FDR file is unadjusted. When adjusted for known pressure and temperature on the day it showed the plane at the right altitude for the airport prior to take off and also at the right altitude according to radalt when flying at normal speed. So it appears the altimeter was not defective.
mono,
The plane had pretty well pulled out of its descent in the last few seconds so it seems hysteresis would not have been significant. It is likely that the discrepancy between radalt and pressure is due to the plane being outside its calibration envelope, as you suggest, and that unusual airflow around the static source would be suspected. The fact that GPWS was operating does imply the radalt was functioning.
winglit,
The plane was almost straight and level at the end so there would be no significant error in the radalt reading due to angles.
FlightPath OBN,
Temperature and baro were allowed for when calculating the pressure altitude.
sycamore,
Thanks for the info about the 'pressure error graph' for the ASI,and the altimeter. The plane in question was a Boeing 757. I do not have access to a manual. Is there any way to get hold of this graph?