I have now written a program that can decode the compressed parts of
the FDR file. The program and output files are available here.
decodes the uncompressed parts of the raw Flight Data Recorder (FDR
commonly called "black box")
file for American Airlines Flight 77 (AAL77) included by the US
Transport Safety Board (NTSB) on CDROMs provided in response to FOIA
(Freedom of Information Act) requests for information regarding the
events of September 11th 2001.
program allows you to selectively
uncompressed parts of the FDR
generate a Comma Separated Value (CSV) file containing the selected
information. The first line of the CSV file contains the parameter
and it can be opened by various programs including Microsoft Excel and
Microsoft Access. Up to 4 subframes of uncompressed data is generated
in the file each time the FDR is started up which I believe happens
when the engines are started. After that, data is stored in a
compressed form which this program can not decode (which is
why I call it a partial decoder). Most of the data in the FDR file is
The method which the program uses to recognise uncompressed
data is not fool proof so it attempts to decode some of the compressed
data as if it were uncompressed. This shows up as lines with unusual
subframes appear in the output in my best estimate of the order
they were recorded. For more details see the entries for the
Position, Bit Offset and Flight Stream Number parameters in Notes
on Parameters for the AAL77 FDR
the NTSB provided CSV
files generated from the FDR file which
were also included on the CDROMs, I have created this program to decode
information not included in
the NTSB CSV files.
As I am providing this program free of charge, it is provided as is.
I take no responsibility for what the program does or doesn't do.
However, you can email
feedback to me (Warren Stutt).
will need to download a copy of the FDR file American
can download a copy from here.
You can also
get an ISO image of the entire CDROM that
I received in response to my FOIA request which
includes the FDR file from here.
Click on the button to choose
location of the file. It is the file \AA77 FDR\American 77.fdr in the
Each subframe appears on a separate line in the output file. Subframes
are recorded in the FDR once per second.
Put a tick in the Include Incomplete Subframes check box if you want to
also include incomplete subframes in the output. Incomplete subframes
will most likely have some valid information and some invalid
information. The invalid information will likely consist of unusual
values and zeroes. If you do choose to include the incomplete
subframes, you will
probably want to mark "Incomplete Subframe" as one of the included
parameters in your output file (More on this below). This will let you
which lines may contain invalid information.
Put a tick in the Maximum One Line Per Subframe check box if you want
only one line to be output for each subframe. This is the default
option. If the check box is cleared more than one line will be output
per subframe for the acceleration parameters since there are several
for these parameters recorded in each subframe. If the check box is
only the first line will be output for each subframe.
The first time the program is started; all the parameters are listed in
Excluded Parameters list box. Only the parameters listed in the
list box are included in the output file. I have grouped some of the
parameters that have similar names together so each entry in the
Included Parameters list box can create more than one column in the
To move fields form the Excluded Parameters list box to the Included
list box, first select a parameter by clicking on it. You can select
than one parameter by holding down the SHIFT or CTRL keys while
the parameters. Then click on the
button to move the parameters you selected across. You can move all the
parameters across at once by using the button.
Similarly parameters can be moved back from the Included Parameters
list box to
the Excluded Parameters list box by using the and buttons.
Once you have selected the parameters you want included, click on the button to choose
where you want the output file to be saved and to generate the file.
All the program options will be disabled (greyed out) until the file
has been completely generated. Close the Output Progress dialog box if
you want to cancel generating the output file.
When you exit the program, the options you selected will be saved in
file AAL77FDRPartialDecoder.config.xml in the same folder as the
reloaded next time you start the program.
The information that the program uses on how each parameter is stored
the subframes is mostly from this file.
information see Notes on Parameters for the AAL77 FDR
Go back to the AAL77
FDR Partial Decoder