skwinty and ChristiaanJ
Yes the altitude data is unadjusted in the FDR file. We know it is unadjusted because in all 12 flights on the file there is no jump at the transition level on ascent and descent. The units of the data are feet, so two steps were used to arrive at True altitude, first converting the feet back to pressure then calculating True. On the ground at Dulles this gave the published elevation for Dulles, after adjusting for baro and temp, so we know it is based on standard atmosphere, and so should give correct altitude at destination by applying destination baro and temp. What it gave at the last position was 124 feet higher than radalt plus ground elevation.
The radalt appears to be reliable and accurate on the ground as all 12 flights show -6 feet while on the ground. If we add 16 to this we get wing height, allowing that the radalt should read zero on touchdown. The last radalt reading was 4 feet, giving a wing height of about 20 feet, which looks about right as the plane still had a little distance to go before impact.
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