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I've been trying to decode a file that is (supposedly) ARINC 717. According to all the literature I've been able to find on ARINC 717, the data should be separated into 4 repeating, one second frames, the start of which is delineated by a frame start code or 'barker' code. According to the literature, these codes should be 001001000111, 010110111000, 101001000111 and 110110111000.

I would therefore assume that these codes should appear an approximately equal number of times throughout the file, but this is not true. I've constructed a code to iterate through each combination of bits and log the number of times these codes occur, and the results generally show that the 1st and 4th codes appear a large number of times (thousands to tens of thousands), but the second and third codes only appear a handful of times (tens to hundreds). This seems very inconsistent with the literature of ARINC 717. I have tried these codes most and least significant bit first. I have assumed therefore that the data had been processed in some additional way, be it encryption or compression, but I'm at a bit of a loss.

Are these codes correct, and is there a gap in my logic?

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    $\begingroup$ Providing a small, relevant sample of the data would make this far less of a shot in the dark. $\endgroup$
    – user71659
    Commented Jan 25, 2023 at 19:42
  • $\begingroup$ @AdityaSharma I’m not sure if you’re familiar with ARINC, it is both the aviation electronics standards body, and simultaneously a private company. Devices in the aircraft use ARINC protocols as the way they communicate with each other, and to communicate with ground services. There’s over 100 different ARINC standards and 717 establishes the data format for flight data recording. See en.m.wikipedia.org/wiki/ARINC. I believe that the reason the OP didn’t provide more context is that it’s a question that can’t be answered without the person already having ARINC expertise. $\endgroup$
    – Max R
    Commented Jan 26, 2023 at 4:24
  • $\begingroup$ @MaxR Alright, sure 👍 $\endgroup$ Commented Jan 26, 2023 at 5:52
  • $\begingroup$ This is correct. I also can't provide a sample of the data for commercial reasons, apologies. $\endgroup$
    – C.Marsden
    Commented Jan 30, 2023 at 11:01
  • $\begingroup$ Barker codes are used for frame synchronization, due to their strong autocorrelation property, along with error correction codes. They are in the frame preamble, not part of data, therefore you may not be able to see them in the frame data. $\endgroup$
    – mins
    Commented Jun 23, 2023 at 15:40

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After consultation with a third part organisation, I've discovered that the issue here was that there was an additional layer of proprietary encoding above the Arinc 717 that rendered this approach useless without information on this additional encoding scheme.

I hope this helps someone in a similar situation.

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