Panel planning - ILS and VOR or not?

[NTex]

I don't have circuit breakers

I have ATC style fuses in a fuse block that is accessible from the forward baggage compartment.

Prior to this conversation I couldn't think of any reason I would want to disable my primary COM/NAV in flight.

just get longer arms

my mistake, assumed you had conventional breakers or a VPX.

 

[mburch]

I see quite a few posts about GPS antennas becoming transmitters presumably when the op amp oscillates after water ingress. Water disrupts a delicate balance in the op amp circuit. GA35 may be not better or worse than any other. May be some cracks can develop and let in moisture. Seem like a checklist item on loss of GPS should be to power off external antennas one at a time.

Yes, there have been some known cases where these antennas have been damaged by overzealous tightening or incorrect hardware, leading to eventual water ingress. A Garmin representative posted the following on another forum around ten years ago:

there are some situations where the internal antenna goes into an oscillation mode and transmits at the 1.575 GHz frequency and then will knock out other GPS units. We (Garmin) sent out a communique to our dealers in 2010 to alert them of this. On some test antenna's we've had returned we've actually found that in some instances the installation is possibly cracking the outer casing allowing water intrusion which will also cause this in our testing. These antennas require very little torque to mount actually specified at 11 to 15 inch pounds which is less then 1 pound of force begin turned with your wrist. Most grownups can do this very easily with a screwdriver so having these installed with the proper tools is the key.
Now to clear up some comments, this by no means is this a common issue in the grand scheme of things, we've had this problem on less then 1% of the antennas sent to the field. When we exchange them we test all of the returns and believe it or not we've only been able to duplicate this on less the .5% of the returned antennas so it's a very hard problem to diagnose. There also is no serial number break for this problem, we've worked closely with the antenna manufacturer and they have implemented some changes at different serial number levels however there has been no definitive serial number where this problems occurs. Remember if it's not installed correctly no unit will survive when the casing shows stress cracks over time.

From the antenna installation instructions for the GA 35 antenna:

 

[KatieB]

A lot of people are happy with GPS only, but if you think through all the what-if scenarios, I don't think it's enough. Dugaru mentioned the GA35 antenna failure mode where it interferes with all the GPS receivers in the aircraft. That is very rare, but it's happened. For that reason and because GPS outages can happen, I would feel vulnerable without a VOR/ILS receiver on board. No real need to spend big $$ on the GTN, you could just add a SL 30 or its new equivalent to a basic IFR GPS/Com like GNC 355 and get 2 comms and 2 different navigation systems.

 

[CaptPausert]

GNC 355 current price $6800, Current version of the SL 30 is the GNC 215 $4500. Total price $11,300
GTN 650XI Nav/com/gps $11,600.

Not much savings there.

 

[BobTurner]

GNC 355 current price $6800, Current version of the SL 30 is the GNC 215 $4500. Total price $11,300
GTN 650XI Nav/com/gps $11,600.

Not much savings there.

Or, for less than $500, buy a hand-held with ILS capability, for emergency use. I have an ancient Sportys hand held with digital to/from VOR bearings. I’ve flown vor approaches under the hood with it, it works. But with so few vor approaches anymore, I’d recommend one with ILS needles.

 

[777drvr]

GNC 355 current price $6800, Current version of the SL 30 is the GNC 215 $4500. Total price $11,300
GTN 650XI Nav/com/gps $11,600.

Not much savings there.

There are significant savings if you want two comms .