Adahars failure

[Jrskygod]

There is a lively discussion over at VAF concerning the Lancair crash and the inability to recognize adahars failure in IMC timely without some sort of tie breaking horizon information. The Garmin folks have been very active in discussing the G3X failure resolutions and I am curious to get the Dynon input on the subject.

 

[cmgolden]

My understanding is that upon a complete failure of one ADAHRS, the other automatically becomes the primary and is relied on for presenting PFD information.

And in the face of present (i.e. not a total failure), but inconsistent attitude data between the two ADAHRS, Skyview merely reports the inconsistency and allows the pilot to display both ADAHRS and manually disable the apparently wrong one. (Ref Pilot's Guide, Rev W. 4-25.)

Could the system instead do automatically what a pilot in IMC would need to do? (Which, I guess is check altitude/Vertical Speed/turn rate/heading/slip-skid data and compare to the attitude shown in order to "guess" which ADAHRS is the correct one and which has failed?)

Seems like a computer could better/quicker determine which attitude is internally inconsistent with its other data and automatically switch to the other one (and advise of that failure, perhaps giving the pilot an option to countermand the automatic switch).

 

[Jrskygod]

ChrisG - that is my understanding as well. I'm not sure if I understand what will happen if one side of the DASB is compromised? Additionally is one ADAHRS communicating to Skyview on one side of the DASB and the other ADAHRS communicating on the other? I would like to know how these things are working together and the possible failure modes. I'm currently using a D1 as a tie breaker in the event I get the "choose one" screen or in the event of a total failure. My concern with this setup basically comes from what I can expect if the Garmin antenna begins oscillating as has been reported several times and is a known problem. Although rare it is a concern as I have no idea if I will loose GPS reference on the Dynons as well and since the Skyviews and D1 use GPS as part of their attitude solution will they show an inaccurate attitude display? All my GPS antennas are within 3 feet of each other and relocating them will be a hassell if needed.

 

[Dynon]

We've actually considered adding some guessing / helper features in the case that ADAHRS disagree, but there are many scenarios here, and figuring out truth gets tricky, even for a computer, in many situations. So while we do share that goal, we want to make sure any "guessing" we do doesn't lead you astray.

As for the network: At any given time, one of the DSAB channels is used for all SkyView Network device communications. If that network is unusable for any reason, the other is used and you're warned that you no longer have network redundancy. On the other hand, if an individual module fails, or if it is malfunctioning in a way that isn't communications-related, it's failure will not impact the other modules.

GPS is ONLY used for attitude aiding if airspeed were to fail. So an oscillating Garmin antenna wouldn't affect you attitude UNLESS you were already in a failure mode of not having airspeed. Although, all that said, we've heard of momentary position blips, but nothing so systemic that your GPS speed would be drastically affected in a way that would affect attitude aiding.

All that said, we'd recommend that your primary GPS source on a SkyView system - even if you have a third-party GPS - be either an SV-GPS-2020 (for systems that don't have a certified / ADS-B Out compliant position source in their certified IFR GPS navigators) or an SV-GPS-250 (for systems that do have such a position source on board). The SV-GPS sources provide multiple updates per second for SkyView and are known to provide a reliable GPS position that do not oscillate or otherwise misbehave.

 

[Jrskygod]

Thanks for the clarification Dynon. The more we know about how these systems work and work together the easier it will be to troubleshoot and be prepared to analyze failure modes.

I personally like the ability to "choose" which adahrs to believe based on a third reference. Your DASB network was the primary reason for me to select Skyview for my panel. I just don't like the failure mode of a CAN bus system.

I am using your SV-GPS-250 antenna for my Skyview system. That antenna is sitting along side of my Garmin 430 W antenna. My concern was if the Garmin antenna fails and begins oscillating would it affect the attitude displayed on the Skyview. As I understand your response - it would not as GPS is only used in that application for aiding if airspeed were to fail. To have the airspeed and the Garmin antenna fail at the same time I believe would be a very remote possibility.

Concerning the D1 which I am using as a third attitude reference - Would the Garmin antenna failure give me incorrect attitude readings on this device? It also uses a GPS antenna for input and my antenna is also located within 12" of the Garmin antenna.

 

[Dynon]

If something knocks out your GPS connection (like an offending third party antenna that is oscillating and blanking the GPS signal to other devices by broadcasting a destructive signal), the D1 will continue to function for a short period of time (a minute or so). Fundamentally, it needs GPS speed for attitude aiding and cross-checking.