dual adaptive failure mode

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330drvr
Posts: 69
Joined: Sun Mar 24, 2013 5:30 pm

dual adaptive failure mode

Post by 330drvr »

I have dual adaptive AHRS feeding dual Horizon HX. AHRS 1 feeds the left HX (normally PFD) and AHRS 2 feeds the right HX. Yesterday the left PFD was off in pitch. I was VFR so no flight issue, but I realize I know very little about the failure modes of this dual AHARS.
Does it alert me that the two AHRS are in disagreement? It bothers me a bit if I had been taking off in IMC conditions. Could you provide a brief discussion of what happens when one of the AHRS has a problem?
By the way, it seems to working fine right now in the hangar. Think it might have been "cold."
RV-7A
Dual HX, Mini X, dual adaptive AHRS, GRT EIS
GRT_Jeff
Posts: 794
Joined: Tue Dec 11, 2012 12:11 am

Re: dual adaptive failure mode

Post by GRT_Jeff »

The Dual AHRS is actually two independent AHRS computers and sensors in one box. They can't talk to each other inside the AHRS box so it's up to the displays to do any sort of cross-checking. If the AHRS are only wired to separate displays then the displays do not compare them for you because they don't see the data from both. AHRS data doesn't go over the display link so in order to do cross-checking the display has to have inputs from both AHRS. We'd like to do more cross-display comparison over the display link in the future but that doesn't happen now.

When a display has inputs from two AHRS, the AHRS are considered to be in agreement if they stay within 7.5 degrees of roll and 5 degrees of pitch. This will be indicated by "Dual AHRS" in full screen PFD or "D" in split screen. In Dual AHRS mode the attitude data is averaged between the AHRS to get the result on the PFD. If the AHRS exceed these limits each EFIS display will show one AHRS as indicated by yellow "AHRS1" and "AHRS2" (full screen) or "A1" and "A2" (split screen) indicators and it's up to you to figure which one to use by checking all available information. There are some accuracy estimates in the plans to help with that using AHRS sensor data. If each display only has one AHRS input then they only see a single AHRS each so they won't have these indicators.
330drvr
Posts: 69
Joined: Sun Mar 24, 2013 5:30 pm

Re: dual adaptive failure mode

Post by 330drvr »

Thank you, that is very helpful. I do have both AHRSs wired to both displays. I now better understand the significance of the "dual ahrs" display.
RV-7A
Dual HX, Mini X, dual adaptive AHRS, GRT EIS
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