If there was a conspiracy theory sub forum here, I would say this thread is heading in that direction.
Hopefully it won't go too far down that road.
To sum up and continue on topic.
gravity32 asks -
"Can you explain why you personally think the pressure altitude is more reliable than the radalt?"
MadFLT already answered this back on post 15.
You really can't compare the two. they aren't even really measuring the same thing. Depending on what you actually want to know, either may be better/"more accurate".
http://www.pprune.org/6697454-post15.html
When Radalt is compared to True Altitude (MSL) over a known object (such as the runway), Radalt is within 2-8 feet of True Altitude once runway elevation is added to radalt, as would be expected.
Flight Data Expert Confirmation: No Evidence Linking Fdr Data To American 77 - Pilots For 9/11 Truth Forum
For some reason, Frank Legge omitted this from his paper and continues to dodge such analysis. It is obvious why he does, as it is fatal to his argument with respect to an "altitude divergence" along the approach corridor for the approaches cited in his paper. It is clear the divergence between radalt and pressure alt was due to the radalt measuring from the tops of buildings, etc, till the aircraft got over the runway threshold.
Also for gravity32, the reason you do not see a step in the altitude data at FL180 from the FDR files, is because the FDR records Pressure Altitude
only. ie. 29.92. You must adjust the Pressure Altitude data using local barometric pressure to get a True Altitude (MSL). The Baro Cor column in the FDR data has this information. A detailed explanation of this can be found here with respect to the CSV files supplied by the NTSB vs the Animation reconstruction done by the NTSB.
Flight Data Recorder Research Team Presents... - Pilots For 9/11 Truth Forum