The output from the program closely matches that from the NTSB CSV files for the period of time that the NTSB CSV files cover. (You can read about the NTSB CSV files here). I did not work from an official Data Frame Layout, so I picked out which parts of the subframe represent each parameter by looking for correlations between the binary data in the subframes and the values of the parameters in the NTSB CSV files. There is no guarantee that I have done this correctly although I believe I am fairly close.

For the single bit parameters that only have two values (i.e. the ON/OFF type of parameters), I looked for bits in the subframe that perfectly represent the values in the NTSB CSV files. In some instances I had more than one choice of bit in the subframe that could be used to represent a parameter. Sometimes I made a choice as to which one to use by eliminating conflicts. Other times I made a choice based on consistency. Sometimes I used the same bit in the subframe to represent more than one parameter in the NTSB CSV files. I was always able to find a bit in the subframe to represent each of the single bit parameters in the NTSB CSV files.

For the numeric values, I looked for parts of the subframe which represented a binary value that had a linear relationship with the values in the NTSB CSV files. I considered an error of 1 in the last decimal place as still good enough to be correct. I was successful in finding binary values in the subframes except where noted below.

There are many other parameters listed in the NTSB's United Airlines Flight 93 FDR Report (available here) that the program currently doesn't handle. If there are any that you are interested in tell me (Warren Stutt) about them and I'll consider including them.

CONTROL COLUMN POSN-CAPT
The best match for the binary value in the subframe that I found had an almost but not quite linear relationship with the parameter in the NTSB CSV file. The maximum difference between the output of the program and the NTSB CSV files is 0.248 degrees.

FLAP HANDLE POSN
The best match for the binary value in the subframe that I found has positive and negative values, however where a negative binary value appears, the corresponding value in the NTSB CSV files is 0. The parameter in the NTSB CSV file uses 5 decimal places whereas 2 decimal places would seem more appropriate. The maximum difference between the output of the program and the NTSB CSV files is 0.00012 degrees.

FL CH MODE OPER
IAS
On these 4 pairs of parameters, I made an arbitrary choice as to which way around the bits in the subframes should be assigned. They could as easily be all the correct way around as all reversed. Both ways around produce a perfect match with the parameters in the NTSB CSV files.

MANUFACTURER CODE
The NTSB CSV Files give the single value of Honeywell in this parameter. The program gives the single value of 3 in this parameter. I chose the location of this binary value from the fact that together with the MANDATORY S/W P/N CODE, ACMS S/W P/N CODE and the VENDOR DATABASE CODE parameters it follows a similar pattern to that in the shortened Data Frame Layout for American Airlines Flight 77 available from UnderTow's site here.

PRES POSN -Data
PRES POSN
These parameters do not appear in the NTSB CSV files, so I looked for correlations with positions I calculated from the VOR/DME navigation aid parameters. I obtained the positions of the VOR/DME navigation aids from AirNav. The Most Significant (MS) data is only recorded once every 64 subframes, whereas the Least Significant (LS) Data is recorded in every subframe. I have combined these values to produce the PRES POSN LAT (DEG) and PRES POSN LONG (DEG) parameters, however since the MS and LS data are recorded at different frequencies, I have provided the option to include the uncombined MS and LS data fields. If you choose to include all subframes in the output, the first values in the PRES POSN LAT (DEG) and PRES POSN LONG (DEG) parameters will be incorrect because of these different frequencies.

RADIO HEIGHT
These four parameters do not appear in the NTSB CSV files, so I looked for correlations with the altitude parameter for altitudes less than 4000 feet. I found values that they behave similarly to the Readout 2 Alt.Rad values provided by UnderTow for American Airlines Flight 77. It is quite possible that I have mixed up the naming of the parameters between CAPT, LRRAL, LRRAR and LRRAC but I believe the values should be in separate parameters since the port names are different in the NTSB's United Airlines Flight 93 FDR Report available here

RUDDER PEDAL POSN
The best match for the binary value in the subframe that I found had an almost but not quite linear relationship with the parameter in the NTSB CSV file. The maximum difference between the output of the program and the NTSB CSV files is 0.037 degrees.

STATOR VANE POSN - L (IN)
STATOR VANE POSN - R (IN)
The NTSB CSV Files has two parameters with the name STATOR VANE POSN (IN). It would appear from the NTSB's United Airlines Flight 93 FDR Report (available here) that they should have different names so I have given them different names.

Go back to the UAL93 FDR Decoder page.