Afs gps wiring

[rvdave]

I'm seeing a limitation how my screens are configured regarding afs gps useage if I have my mfd fail or if I need to shed a current load. I would at times like to have only pilot pfd on. Because of the mandatory items needing to be wired to pilot pfd, my afs gps is wired through the expansion cable for power / serial port of mfd. Through vpx I can control power to some other devices wired to mfd when off---ADSB, Nav radio, afs comm, but not afs gps. Can I wire power from vpx to afs gps and still use the gps data through serial 4 of mfd even though its power will be off?. Here is configuration I have right now:

Pilot Pfd
Ser 0---VPX
Ser 1---XPDR
Ser 2---A/P
Ser 3--ARINC
Ser 4--Avidyne gps navigator

MFD
Ser 0-- AFS comm
Ser 1--ADSB
Ser 2--PAC 15 audio panel
Ser 3--VAL Nav
Ser 4--AFS gps

[rleffler]

Dave,

While I'll defer to AFS for a formal answer, I'll share my opinion.

Since data from the MFD will be passed to the PFD via TCP and the MFS doesn't have power, I don't believe that will be possible if the Ethernet port is non-functional.

Also, I believe that the AFS GPS is a 5v device, which will make using the VPX as a direct power source more complicated.

My curiosity question is if your Avidyne is connected to the PFD, what other GPS function do you need to provide if the MFD is dead?

bob

[Shawn McGinnis]

Correct, that's why we recommend your primary GPS (Avidyne) is connected to the PFD and the backup (-250) is on the MFD. Bob is also correct about the power issue. The puck is designed to run at 8v so you would need a DC-DC converter and another serial port available on your PFD to wire it to both screens.

[rvdave]

Dave,


My curiosity question is if your Avidyne is connected to the PFD, what other GPS function do you need to provide if the MFD is dead?

bob

Well none really as long as things are working but I am looking at what if scenarios, mainly if I were to have the Avidyne offline for either fault, service, or load shedding; then I would hit a dead end regarding Nav options if I lose the mfd for whatever reason. Maybe unlikely, but it's scenario I would at least like to have covered with some kind of option, maybe there's something I'm not seeing that could give me an option.?

[rleffler]

Well none really as long as things are working but I am looking at what if scenarios, mainly if I were to have the Avidyne offline for either fault, service, or load shedding; then I would hit a dead end regarding Nav options if I lose the mfd for whatever reason. Maybe unlikely, but it's scenario I would at least like to have covered with some kind of option, maybe there's something I'm not seeing that could give me an option.?

I would suggest the following decision tree:

Avidyne fails:

If VFR continue using AFS GP on MFD
If IFR, declare an emergency and land, or cancel IFR and continue VFR

You are going to get all wrapped around the axel if you start worrying about double and triple failures. The end result most likely will be something more complex and introducing more failure points.

A suggestion would be to get something like a G5, D2, or Gemini as a tie breaker to determine if which screen is correct should one of the ADAHRS fail. It can also function if you get a double EFIS failure (highly unlikely), but then you're back into the game of which GPS to drive the screen (or do you install a third one?). Or you can get a SL-30 or some other NAV unit as a secondary backup to protect from GPS jamming. As you can see, there is no perfect silver bullet solution. In any cause our panels are much more resilient than the steam gauge panels that most of use learned to fly with.

[rvdave]

I know you can go pretty deep finding failure modes and that's not my point, although I see this scenario as possible and concerning so per your suggestion I may consider a third puck for third screen as the easiest resolution for gps concern. Thanks