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IFR with ADHRS failure

calpilot

Well Known Member
I have an RV-7 with dual Garmin ADHRS and dual G3X screens. The PFD (ADHRS 1) and MFD (ADHRS 2) are on separate busses, the PFD can be powered from normal ships power or one or both batteries (Main and backup).
I noticed that when I pull the CB for ADHRS 1, I loose the transponder, and the avionics shop did not wire a switch to allow the transponder to receive information from ADHRS 2. Not a good thing when in the clouds and have a system loss. I see many aircraft wired the same way. I wired in a TPDT mini switch, labeled it:
TXP ADHRS 1/TXP ADHRS 2 per the following diagram. Now with redundant transponder serial, I feel more confident when inside the milk bottle.
Regards,

Gary
 

Attachments

  • TRANSPONDER SWITCHING.pdf
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good catch. I had always assumed that in an emergency, with failed equipment, ATC would find a way to deal with whatever your are sqwauking and could rely on your verbal altitude reports. However, I was sure to wire the ident button from the transponder to a switch on the stick, as idents can be critical in helping ATC to deal with your problem and didn't want to be dependant on the PFD to make them happen.

Larry
 
good catch. I had always assumed that in an emergency, with failed equipment, ATC would find a way to deal with whatever your are sqwauking and could rely on your verbal altitude reports. However, I was sure to wire the ident button from the transponder to a switch on the stick, as idents can be critical in helping ATC to deal with your problem and didn't want to be dependant on the PFD to make them happen.

Larry

I agree with the above, and I think you lose quite a bit of flexibility/redundancy by separating the system that way. Just my opinion.
 
In the Garmin system, I'm not sure if the "Ident" feature will do anything for you if the transponder is not receiving any serial input. Perhaps a Garmin GURU can step in and enlighten us? I was flying today, talking to Center, they were receiving my squawk just fine, I pulled the CB on the #1 ADHRS, and Center said I returned to just a primary target. I then flipped the switch to ADHRS2 and my target returned with all the serial information! Oh Joy!

Gary
 
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