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Thread: experimental IFR GPS

  1. #1

    experimental IFR GPS

    What would be the necessary process for building an experimental IFR GPS?

    Thanks to ADS B we have a number of relatively inexpensive TSO'ed IFR GPS WAAS sensors, so it looks like the "only" part that would need to be experimental would be the actual receiver waypoint sequencing and error display. This would be a matter of software, which I can produce and could be produced as part of an open source project so everybody could use/help over time.

    There are plenty of non-TSO'ed ADIs, EHSIs, PFDs etc being used in IFR conditions, so there must be some sort of customary process for producing and verifying these things, but every time I talk to anyone about it they tell me that its "too hard" without getting specific.

    Anyone at EAA etc have some specific info? With the cost of IFR GPS being so very high these days, it seems an interesting thing to explore.

  2. #2
    Auburntsts's Avatar
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    Quote Originally Posted by yakman2020 View Post
    What would be the necessary process for building an experimental IFR GPS?

    Thanks to ADS B we have a number of relatively inexpensive TSO'ed IFR GPS WAAS sensors, so it looks like the "only" part that would need to be experimental would be the actual receiver waypoint sequencing and error display. This would be a matter of software, which I can produce and could be produced as part of an open source project so everybody could use/help over time.

    There are plenty of non-TSO'ed ADIs, EHSIs, PFDs etc being used in IFR conditions, so there must be some sort of customary process for producing and verifying these things, but every time I talk to anyone about it they tell me that its "too hard" without getting specific.

    Anyone at EAA etc have some specific info? With the cost of IFR GPS being so very high these days, it seems an interesting thing to explore.
    The problem is an IFR GPS has to meet the applicable TSOs (eg TSO non-WAAS c129 and WAAS c145) unlike the flight instruments you mentioned as non-TSO'd examples. Showing TSO compliance requires testing and equipment beyond the reach of most. So I don't see the FAA ever buying off on an "experimental" IFR GPS. Just my $.02 but I'm not an avionics expert by any stretch.
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  3. #3
    Quote Originally Posted by Auburntsts View Post
    .

    The problem is an IFR GPS has to meet the applicable TSOs (eg TSO non-WAAS c129 and WAAS c145) unlike the flight instruments you mentioned as non-TSO'd examples. Showing TSO compliance requires testing and equipment beyond the reach of most. So I don't see the FAA ever buying off on an "experimental" IFR GPS. Just my $.02 but I'm not an avionics expert by any stretch.

    So, thats precisely the question. What is the process, if any.
    I think at that point it might be possible to size the effort. Note, the receiver per se, in otherwords the hardware, is already TSO'ed.

    I'm hoping some folks who have worked on non-TSO'ed avionics might have some info.

    To save some time, I've already looked at the applicable advisory circular, TSO C149, 161b and 162b, 192 etc.

    They don't say anything specific other than "meets DO-178B" which is also pretty non-specific.

    Is the only way to do IFR GPS to be garmin?

  4. #4

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    I have to report that saying DO-178 is non-specific is kind of like saying that FAR Part 23 is non-specific about certifying airframes. DO-178 is up to rev C and requires full documentation of system requirements, design documentation that describes how the software implementation supports the requirements, unit, integration, and full system test with documentation of results. Winds up being a pretty big paper package that describes how your hardware and software does what you say it does, reliably and repeatably, every time. The paperwork, and particularly the test documentation, is a pretty big burden for a hobbyist who has to have a day job.

    You can build a GPS based navigation system around the available components. Fly VFR and have fun. For IFR Garmin has a big head start on the rest of us. The regulatory burden is a big barrier to folks who want to compete with them. And in all fairness, they do what they do really well and their gear is well worth the $$.

    The medical device world I live in is very similar. 21 CFR 820 if you need some light bed-time reading.

    Best of luck,

    Wes

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