ADAHRS, EMS, GPS momentary failure

[henryhallam]

Hello,
My Lancair 360 has an early-model D1000 and D700, with EMS, SV-GPS-250 and dual ADAHRS.

On Saturday on a return flight from Mojave (where the airplane had been parked on a hot ramp for a few hours) I had several momentary in-flight system failures. On both displays the attitude and EMS pages were Xed out and the map showed a loss of GPS position. This only lasted a second or two on each occasion, though the attitude and synthetic vision took some time to fully recover. I had four or five of these occurences, and there seemed to be some correlation with flight through light turbulence. When I landed I downloaded the diagnostic data.

I thought perhaps it was due to heat from being parked in the sun, but it happened again while taxiing and while flying in Monday's cool weather. I tried pulling the circuit breaker so the D700 wasn't running at all and the D1000 was running from its internal backup battery, but I still had a couple of failures. I haven't tried running from the D700 alone.

My first guess is a wiring problem, but why would that affect the SV-GPS-250 which is attached via serial port at the same time as the ADAHRS and EMS which are on the Skyview Network?

Any thoughts appreciated.

 

[henryhallam]

Also worth noting that there was no apparent effect on other avionics (e.g. SL30, audio panel) and I didn't notice any bus voltage fluctuations.

 

[Dynon]

Were there any residual warnings or messages other than the ones related to the loss of information?

There's nothing completely obvious here that would cause such a loss of information, even momentarily. If there were a SkyView Network problem, we wouldn't expect the GPS position to be affected. If there a power issue, you'd expect to see a reboot as well. If a display were switching to battery backup, you shouldn't expect any loss of information except for the "power lost" message that lets you know you're on the backup battery. Your test to isolate the other display as well will be helpful, though.

 

[henryhallam]

No reboots. As far as I recall, the only residual warnings were related to the attitude recovering and on one occasion an ADAHRS cross-check error that also disappeared after the attitude filters had reconverged.

Did you see anything in the diagnostic files?

Inside the display units, does the power to the Skyview Network devices come from the same source as the power to the GPS and other RS-232 devices? If that had briefly shorted out, either inside a Skyview unit or one of the external devices or in a harness, would it take down all the devices but not the displays themselves? How is the power output to devices arbitrated between displays?

I will fly again tomorrow on the D700 only and see if I can reproduce.

Thanks

 

[henryhallam]

Same issue running on the D700 alone with the D1000 powered off (but still wired in to the network)

 

[Dynon]

So actually, one of my engineering colleagues has a theory. Either the power line that goes from the SkyView display to the SV-GPS-250/2020, OR one of the power lines on one of the SkyView Network cables (these are on pins 7/9), is getting repeatedly grounded intermittently (ie - "vibrated" to ground). If it were grounding out period, the system can figure things out, but if there is an intermittent grounding it gets more complicated.

 

[henryhallam]

OK, that would fit with the correlation with turbulence, taxiing over bumps, "firm" landings etc. I'll take a look at the wiring over the weekend. Thanks for the insight!

 

[henryhallam]

Your engineer was spot on. Found one of the red/white ("power 2") wires in the network harness was rubbing on a grounded aluminum bracket and had abraded through the insulation, causing an intermittent short (and little sparks!). All better now.

Obviously this was a case of less-than-clean installation, but it might be a good idea for Dynon to consider shipping the pre-built harnesses in jacketed multicore cable rather than individual wires.

 

[dynonsupport]

Henry,
Glad you found the issue.

Sounds like you're one of our earlier SkyView customers. The wiring harnesses we have sold for about the last 4 years have a second jacket on the wires like you mentioned. The downside being they are quite a bit stiffer, so everything is a trade-off.