AXP340 ALT available if IFD540 GPS failure?

I have an IFD540 & AXP340 with squat switch connection from the 540 to the 340 for GND to ALT switching on takeoff.

The IFD540 GPS failed at start up last week (failure msg after a few minutes and large X in the HDG rectangle). Since the 340 didn't auto-switch into ALT state, I tried to do so manually after takeoff but without success.... so my xpdr was effectively inop as far as ATC was concerned.

I haven't found anything in the manual to help. Is anyone aware of a way to get the 340 into ALT state in this situation?


Edited by chflyer - 03 Aug 2015 at 5:20am

While browsing the transponder setup menu (hold FUNC while powering up the transponder) trying to sort out my still-unresolved pressure altitude problem, I saw several options for the air/ground switching.    If it was stuck in ground mode because of a GPS failure, I think you could go in and change the squat switch setting to "not connected" so that the transponder would default to ALT.

chflyer wrote: I have an IFD540 & AXP340 with squat switch connection from the 540 to the 340 for GND to ALT switching on takeoff. The IFD540 GPS failed at start up last week....

Steve,

Could you comment on the current software release behaviour?

My 440 will be added shortly, but the current IFD540/G430/AXP340 wiring doesn't have the G430 connected to the 340, so if I need to have both the 540 and 440 feed the 340, then they'll need to go back into the panel and rewire, which I would like to avoid.

Essentially, what I'm looking for is an easy way to get the transponder into alt mode if the 540 gps feed goes u/s. As mentioned in my first post, when the 540 gps wouldn't come online (with software 10.0.3.0), the altimeter wouldn't come out of gnd mode since without the gps squat feed to flag sirborne it only has GND-SBY options as long as it thinks it is on the ground (p5 of the 340 PG).

Thinking it through, going through an AXP reconfig during climbout because of ATC complaints about no mode C is not a good idea, especially in IMC. This is the situation that I encountered, but luckily VMC.


Edited by chflyer - 09 Jan 2016 at 12:31pm

Thanks for the input Orest. Let's see what Steve says. I haven't seen the advisory. I also haven't had any GPS outages since then, but as mentioned would like to avoid going into the panel again when I add the 440, just to also wire it to the AXP340 as backup due to a logic issue.

Hi Vince,

Let's reset the problem statement for clarity.     Is it true to say the problem you are trying to solve is:

1.  Allow for automatic transition of the AXP340 from GND to ALT and back to GND during normal flight operations, and;
2.  Allow for a means to manually get the AXP340 into a desired mode in the event the IFD540/440 is inoperative?

Here's how the system works right now:

IFD540 Release 10.1.1.0 with AXP340 transponder:

On the ground:

Loose GPS --> Can only manually cycle between GND and STBY

 

In the air:

Loose GPS --> Can only manually cycle between STBY and ALT and ON.

I presume the issue you are asking about is if you are on the ground and you lose GPS then decide to takeoff, how do you get the transponder into ALT or ON and conversely, if you are in the air, lose GPS and GPS does not recover before landing how do you get the transponder into GND, right?

Steve,

Any info, given my "yes" answer to your presumption?

I neen to give my shop guidance on Monday regarding wiring both 540 & 440 to the 340.

Vince

David,

I agree and have the same approach with the xpdr.

I assumed, perhaps in error, that if a manual GND override to force ALT were available, then the reverse would also go with it. But you are right that switching to ALT is more important than switching to GND. Running in ALT mode on the ground can be explained if ATC complains, but operation in the air without mode C would often be a regs violation.

BTW, does anyone know if gps loss in the air causes reversion to GND mode on the 340 in the air? I would think that it would.

I still need an Avidyne position on this and wiring both 540 & 440 to the 340 since my shop claims that Avidyne does not really recommend it and they don't recommend the necessary diode.

Vince

I'm not getting the issue here.  Since the IFD 540 and I assume the 440 both have ground/air state inputs, why use a squat switch on the gear to do the same thing.  Seems more complicated to me unless you don't have a 540 or 440.  The ground/iar state solution works great for me, especially since my gear is down and welded.

That is interesting,  just had the transponder/Pitot/Static recert done and when the IFD 540 was turned off, the alt Stopped being supplied to the transponder.  So our 540  must be ON for the transponder to put out altitude.

It is routed from the blind encoder via RS 232 to the IFD 540 and passed to the transponder.

(single 540 installation)

Previously with another 540 unit installed, when the GPS died, it reverted to ground mode in flight.

Diesh123, same installation but different units installed?

Edited by flybikeski - 11 Apr 2016 at 8:58pm

I had some trouble with my IFD540 and had to make a couple of flights with its breakers pulled.  My AXP340 worked just fine without it; I flew through Class B talking to ATC with no complaints, so it _can_ work that way.

Edited by MysticCobra - 12 Apr 2016 at 12:00am

Diesh, your avionics shop was able to turn your transponder on for the cert because Avidyne added a maintenance selection just for that reason.

Edited by tony - 12 Apr 2016 at 7:43am