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Garmin GNC250XL upgrade to 300XL

Radioflyer

Radioflyer

Well Known Member
My VFR RV currently has a GNC250XL coupled to a TruTrak AP. I would like to have at least a minimal level of IFR capable avionics. If I could find a really cheap GNC300XL, would it be a simple exchange and plug in to the existing tray?
 
Not exactly…. The unit would probably operate, but to be legal for IFR the 300XL needs an annunciator panel with a couple of switches (see the AK950) So there would be wiring involved, and a panel modification needed. What do you use for a CDI?
 
Panel currently has a King CDI (probably a KI202) driven by a KX155 nav/com (without glideslope). The 300XL doesn't provide vertical guidance, so can it drive King CDI or would I also have to get a seperate CDI for the 300XL? I guess there are several ways to go for minimalist IFR, given legacy equipment..just trying to navigate cheapest least effort approach.
 
The GPS can definitely drive the King CDI. Does the 250 currently drive the King CDI? If not, there are quite a few wires to add because the AK950 (or equivalent) needs to switch between sending the VOR/Loc and GPS signals to the CDI. That (of course) requires the more expensive AK950 due to all the switches needed.
You can also add a second CDI directly connected to the GPS, which eliminates the need for switching and somewhat simplifies the wiring but now adds the cost of a CDI.
If you have any sort of EFIS that has a CDI, then a simple 2 wire RS232 connection will do the trick (that is how the TruTrak is connected).
Your current setup is probably 'legal' IFR, just limited to VOR nav and VOR/ILS approaches - pretty limiting in today's environment.
I started with a 300XL when I built my RV, and last year upgraded to a GNC355. Already sold the 300XL...
No matter what you do, it won't feel either cheap or low effort...
 
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Yep, VOR based IFR is very limited, and so some minimal GPS based IFR capability is good. The King CDI is only connected to the KX155. No matter what, it's looking like beyond getting a 300XL, I'll be doing some panel work for either a 2nd CDI or EFIS. Well, at least replacing the 250xl with a 300xl won't itself be a problem, which is good to know.
Thanks for your help.
 
Radioflyer said:
Yep, VOR based IFR is very limited, and so some minimal GPS based IFR capability is good. The King CDI is only connected to the KX155. No matter what, it's looking like beyond getting a 300XL, I'll be doing some panel work for either a 2nd CDI or EFIS. Well, at least replacing the 250xl with a 300xl won't itself be a problem, which is good to know.
Thanks for your help.
Click to expand...
Hopefully you’re aware that the 300xl was TSO’d under the old TSO129 rules. To use it under ifr you must have alternate means of navigation, which you have with your kx155. But in practice you may find this a problem: if you’re flying ifr to an airport that has only a gps approach, then you have to carry enough gas (plus 45 min) to reach an alternate that offers a vor or loc approach. For some trips that can be pretty limiting, along with the higher minimums for non precision approaches. Just be aware you’re buying technology that’s so old it’s no longer produced.
 
Yes, you're right about the tso129 rules, and they are very limiting for IFR work. The rules are more limiting than the old tech! Yeah, it makes marginal sense to go through the trouble with the 300XL "upgrade" unless one is satisfied with just practicing non-precision approaches.
 
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