AAL77 FDR Partial Decoder Help

UPDATE: I have now written a program that can decode the compressed parts of the FDR file. The program and output files are available here.

This program 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 National 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.

The program allows you to selectively decode uncompressed parts of the FDR file and generate a Comma Separated Value (CSV) file containing the selected information. The first line of the CSV file contains the parameter names 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 compressed.

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 values.

The subframes appear in the output in my best estimate of the order they were recorded. For more details see the entries for the Block Position, Bit Offset and Flight Stream Number parameters in Notes on Parameters for the AAL77 FDR Partial Decoder.

Although 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).

You will need to download a copy of the FDR file American 77.fdr. You 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 Choose button to choose the location of the file. It is the file \AA77 FDR\American 77.fdr in the ISO image.

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 know 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 values for these parameters recorded in each subframe. If the check box is ticked, only the first line will be output for each subframe.

The first time the program is started; all the parameters are listed in the Excluded Parameters list box. Only the parameters listed in the Included Parameters 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 output file.

To move fields form the Excluded Parameters list box to the Included Parameters list box, first select a parameter by clicking on it. You can select more than one parameter by holding down the SHIFT or CTRL keys while clicking on 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 Start 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 the file AAL77FDRPartialDecoder.config.xml in the same folder as the program and reloaded next time you start the program.

The information that the program uses on how each parameter is stored in the subframes is mostly from this file. For further information see
Notes on Parameters for the AAL77 FDR Partial Decoder.

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