VSGV source selection - EFIS-430W-530W

[johncleary]

Guys,

The current AFS ARINC 429 wiring diagram 53620WD for the AFS3500 EFIS shows no serial wire going from the EFIS to the VSGV.
I have a 430W and a 530W and I want to be able to drive the AP from either the EFIS or the 430 or the 530.
I have set up two switches through small latching relays. One switch selects which GNS, the other selects GNS or EFIS.
When EFIS is selected, what do I do with the serial lines from the Garmins? Should one of them be connected to the AP or should they both be isolated along with their ARINC lines?

Thank you,
John Cleary

[TrutrakTech]

Hi John,

You can hardwire one of the GNS units into the AP or set up a switch to change the serial input to the AP from one or the other. When the AP is receiving ARINC steering commands, it will "ignore" the serial input other than to display the slaved DG in the top left of the display. So the source of the RS232 doesn't have to be the same as the ARINC source.

I hope this helps. Thanks!

[PhantomPholly]

Additional info: I don't know why the TT folks don't trumpet this as an added feature, but because of this behavior you can have the serial lines hooked up to, say, a hand-held GPS as backup. If for example your GNS failed and your EFIS depended upon the GPS signal from the GNS to generate it's output, you would still be able to use the autopilot driven by the hand-held. Too, if you have wired it to cross-fill your flight plan from the GNS, you need simply press the Mode button to engage the hand-held driven flight plan upon failure of the GNS.

Changing topics, FWIW I would not use latching relays to change source between the GNS and EFIS - I would use a simple DPDT switch. Relays are more likely to fail than switches, and when they do they are more likely to have NO usable "condition" (where, with a switch at least one of the two positions may still work).

[johncleary]

Thanks Guys - I appreciate your help.

John