[calake]

My panel has both a Garmin 496 and a GRT Sport with and internal GPS. I can wire a switch to select which GPS the autopilot uses, but not sure why I would do that. Any comments from those going before? My theory is simple is usually better.

C A Mansfield
N33WE (reserved)

 

[hevansrv7a]

Related but not exactly the same

I have a Garmin '496 which provides serial data to the GRT Horizon and to the TrueTrak autopilot. Since the autopilot is part of my "redundancy" plan, I wired it through a switch to receive the data either from the GRT or from the '496 directly. So if the GRT malfunctions, I can fly the plane via the A.P. and the '496 until VFR can be found. The TrueTrak also can function reasonably well (keep upright and approximately on course) with no GPS, just its internal magnetometer.

If I had your setup I'd consider a switch for which source the EFIS uses. However, I believe that GRT EFIS's are able to integrate two sources to resolve any accuracy issues. For that reason, you may want a 3-way switch. In fact, I think they also use VOR data to check the GPS, but I'm not certain how they do that. It might be worth having a chat with them about this issue. They are very helpful people.

Yes, simple is better, but so is being able to eliminate a point of failure while in flight.

 

[erich weaver]

I have the GRT Horizon I (not the sport) with internal GPS and also a Garmin 296 and TruTak AP. I have no dedicated switch to change the GPS source as it can be changed using the EFIS knobs/buttons. I know this because I once inadvertently switched it and couldnt figure out why my AP was sending me the wrong way. A call to GRT got me straightened out. I'll bet it works the same way on the Sport. Cant tell you exactly how to do it - I have mine set to use the 296 as I prefer that display over the GRT moving map (sure would like to upgrade to the high resolution screen), and so my experience in switching from one to the other is limited to that one time.

erich

 

[Wolf]

Switch

The Horizon installation manual on the GRT website covers this. If your EFIS fails you can use the autopilot direct from the GPS. You will need a DPDT switch either on-on or on-off-on. You only use the two ARINC inputs. The GPS serial goes to both autopilot and EFIS and need not be switched. At least that is what I remember.

 

[SteinAir]

With the 496 and the GRT there are no ARINC's to switch, you'll only need a SPDT switch (preferrably and On/On) if you desire to switch the RS-232 GPS serial feed from the EFIS / 496.

It's a simple install, run the GPS wire to one side of the switch, the GRT wire to the other, and the center post to the A/P. We do it on almost every panel or radio stack we wire.

With this switch, the EFIS can die or be shut off and you can still have the A/P follow the flight plan from the GPS directly.

Cheers,
Stein