I installed a DAC GPSS unit which works which is really cool, but not right away.  On startup the GPS annunciator light blinks which means something is wrong, in this case likely it is not receiving the ARINC 429 data correctly from the 540, no matter how long I wait.  If I power it down and back up, the GPS light is steady and the unit works as advertised.  Unfortunately rebooting it in flight right now is not easy because it is on a non-pullable breaker shared with the MLB100 (each fused separately).  I could get a pullable breaker and pull it each flight to get the thing running, but that isn't very elegant. 

I know others have the DAC unit.  Anyone run into this? Any ideas?

paulr wrote: I have a similar issue, with the same config-- new GDC31 and new IFD540. The GPSS light consistently blinks until I start my takeoff roll, even after the IFD540 has a GPS fix and I've entered a route in the FMS. The light goes solid at around 30kts. GPSS has worked flawlessly in flight, however.

That does make sense - somewhere I saw reference that the GDC31 also looks at the ground speed label and not just the bank angle label in the data stream. 

However mine will stay blinking until I get comfortable in cruise and can deal with it.  For right now it isn't bolted down, so I can reach it, pull the connector off and put it back on, and the light immediately comes on steady.

I have the same thing happening with an STEC 55x, well, sort of.

If I try to engage the STEC 55x GPSS on the ground, it will indicate FAIL. However, if I try to activate it while on the IFD540 legal screen, it WILL activate fine.

For me it is not an issue, as I don't need GPSS "on" until in the air, and would not activate it on the ground -- except for testing purposes (that is how I discovered this). But it does seem to indicate that data that is needed by GPSS is not available on the bus until the IFD540 senses that it is flight mode.

But, as long as it always starts working on the takeoff roll, it shouldn't be an issue. If it won't, then it would be messy, you need a power switch for it.

* Orest

If it won't engage AT ALL, it is likely an install error.

The ASPEN GPSS works just fine with an IFD. I used it for every trip, before I got the STEC 55x installed.

* Orest

edanford wrote: My IFD540 / GDC31 performs exactly like Pauls

Paul and Edanford: Do you guys know if you use a IFD540 ARINC 429 data port, or a RS232 port?

Well, with no active flightplan, there can be no active leg.

* Orest

Gring wrote: I would check with Avidyne tech support on this one.  I know that there was a problem in the previous release where the LIO board booted out of sequence.  This affects the IO of the unit and you can tell if your unit has the issue because while on the legal screen you'll see your HSI/CDI full left, full down deflected.  When this happens, the unit will not cross sync (if you have 2) properly.  Rebooting usually clears the issue.  I'm wondering if you are experiencing this issue. since the ARINC429 would be the same type of IO that falis on the crosssync.  It has been corrected with the current release.

I upgraded my IFD540 unit to the latest and was very hopeful that would do it, but not to be.  The GPS annunciator does go steady for about 5 seconds during the 540 self-test legal screen, but then the DAC unit seems to get confused and requires a reboot. 

Dang.  I guess I'll get a pullable breaker and handle it that way.

Avidyne tech support has been helpful and their current thinking is this: The DAC unit is auto-baud detect and when the IFD540 self test screen comes up, the ARINC 429 data stream is output at low speed, and there I get a steady GPS lamp, and there the DAC unit locks on to that baud rate.

Later the IFD540 comes alive with ARINC 429 high speed, but now that confuses the DAC unit which has already experienced and locked onto low-speed (unless it is rebooted).  The solution may be to set the 540 429 port to low speed and next week I'll test that.

I did test the solution suggested by Avidyne, setting the ARINC 429 port to low speed, and that worked. 

It sounds like STEC does the same thing as the DAC GDC31 GPSS.  There may be other avionics that would also auto-baud-detect and lock on to the low speed output during the 540 self-test and then be unable to reset to the high speed port later.