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Garmin 2 Inch Navigator question in regards to primary IFR navigation source

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Working with a friend who is trying to go GPS only in her Arrow. After talking with her avionics shop of choice, they claimed that the GPS175/GNC355/GNX375 cannot be used as the primary source of IFR navigation and requires a nav radio like an SL30 or something like a GPS400, GNS 430, or GTN 650. I cannot remember where I heard it but I also remember seeing it in text on one of the forms fairly recently. Has anyone run in to this or heard similar?

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I've heard the same.  When I did my upgrade I put in a Garmin GNC255A ($4k).  I did it because I wanted a ground based navigation system but it also satisfies the legal requirement.

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That doesn't appear to be true for any Single Engine piston under 6000 lbs, only for all others - from  the AFMS below.

However, IMO as a CFI-II I wouldn't ever be caught out doing training in actual IMC with only GPS on-board - that's nuts given how easily they're jammed and with almost daily GPS interefence testing NOTAMs putting it at risk of losing coverage. That said, all I ever use to navigate is GPS. But I have lost GPS from jamming 3 times now, including being IMC, (although not yet in US airspace) and each time I was abe to fall back on VOR navigation.  So for me, not even two TSO GPS navigators (which I do have) are sufficient without a Nav radio backup  The Arrow came with 2 nav-com radios, personally I'd want both for an IFR Arrow. 


Edited by kortopates
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The GNC355 can be used as primary NAV in our planes for IFR, as long as you have a second COM at a minimum. Whether you want to have only GPS in your plane or retain ground based NAV is another discussion and Paul brings up some very good points. Here is a post in a different thread which may be the one you were thinking of. I included the information from the GNC355 Installation manual for the GNC355 along with links to an FAA notice from 2013 and the current AIM.


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