Update Letter to the NTSB
Dated 29th December
I have now found the problem that caused
the United States National
Transportation Safety Board (NTSB) to decode almost 4 seconds less data in the Comma
Separated Value (CSV) file they produced from the raw Flight Data Recorder (FDR
commonly called "black box") file for American Airlines Flight 77
(AAL77) than my
AAL77 FDR Decoder. I discussed this issue in the previous letter that I sent
to the NTSB. I have found that this problem was caused by the fact
that the FDR did not record Hamming Code and Page
Parity Error Correcting Codes (hereafter referred to as error
correcting codes) for two 128 byte pages towards the end of the FDR
I previously wrote a Hamming
Code and Page Parity Checker for the FDR file that checks the error
correcting codes. The two pages for which that program shows the error
correcting codes as being incorrect are the pages where the FDR did not
record the error correcting codes.
On 4th January 2011, I posted the
following letter to the NTSB. An ISO image of the CDROM that I included
with that letter is available here.
Details of my
FOIA request that I
referred to are available here.
I will provide an update if I receive a response.
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