AAL77 FDR Decompressor

This program decompresses 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.

One subframe is written per line. The 12-bit words are written in binary with a space in between them starting from word 1 and continuing through to word 256.

The end of a compressed section of data is marked by the line Sync Lost. The last frame before Sync Lost will be incomplete, so the last subframe before Sync Lost will most likely have fewer than 256 words.

You can download the output file generated by the program from here.

To decode the 12-bit words you can use the data frame layouts from here.

The subframe number of a frame can be calculated by treating the first (most significant) two bits of word 1 as a 2-bit unsigned integer and adding one.

Alternatively I have also written an AAL77 FDR Decoder program.

In the interests of transparency in showing that the program is really generating its output from the raw FDR file, you can download the C# source code. I used Microsoft Visual C# 2008 Express Edition to create it. You can look at the .cs source files using any text editor, and you can download the Microsoft Visual C# 2008 Express Edition from Microsoft to compile it. Alternatively, you may be able to get a DVD with the Visual Studio Express Editions from your local Microsoft sales office.

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 if you want to run the program. 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.

A Change Log detailing the changes in different versions is available here.

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