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OTOH, the digital altitude display and "bunch of dots" turn coordinator display make hand-flying using just the Trio display fairly difficult in all but calm weather. But if just used as a "tie breaker" between two EFIS boxes (one says wings level, one says turning), it easily tells you if you're turning, or not. |
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Think of it as insurance. It is better to have it and not need it than need it and not have it. I can't stress enough; Your life is worth more than "a few dollars and some panel space" :cool: |
It was easy for me.
I NEEDED a tie breaker. To me it's just another cost of safely flying IFR. 3 independent ADHRS was what I felt comfortable in the clouds with.
Sure it cost's a bit more, but me and my wife are worth every penny.. I'm sure there are any number of ways to do it. Just always leave yourself an out when, not if, but when things go south. ![]() |
Tie Breakers
Much discussion in this thread seems to imply that we need 3 fully independent AHRS/ADAHRS to have a "tie breaker'. However, just like a traditional 6 pack has adequate information to "tie break" in the event of instrument failure, so do glass panels with only 2 attitude systems. In my RV for example, I have a single AHRS dual display EFIS as well as analog airspeed, altimeter, artificial horizon, and vertical card compass for back up. I also have a Truetrak Vizion AP. In my case, a disagreement in bank between the iron gyro and efis can be resolved by observing GPS (GNS430W) track or the compass. Pitch information disagreement can be resolved by air speed and altitude trends. Heck, I learned to fly a Citabria "under the hood" including unusual attitude recoveries with only "needle, ball, and airspeed". And as others have stated, an independently functioning autopilot (Truetrak in my case) can also be used to stabilize the aircraft to determine which attitude source is correct. And yes, my plane has periodically been flown hard IFR, as well as many hours under the hood.
Skylor RV-8 |
I'm Just Spit Ballin Here,
but it seems like most posters are talking about completing an Instrument flight after they lose a primary instrument. BAD CHOICE.
In the "old days", when we lost our sole vacuum source, we advised ATC (sometimes declaring an emergency) and looked for an exit out of IMC or a quick landing using our turn coordinator, compass and pitot static instruments. You don't need three or four or five independent ADAHARS sources to safely fly instruments, but you do need to know what to do if the dominos start falling, and from my experience, it's seldom to "carry on". Terry, CFI RV9A N323TP |
Both absolutely correct
Both Skylor and Terry above are correct. It's a comfort level and what you are trained proficient too. In any emergncy or abnormal, fly the plane and work yourself out of it.
We had all rather be on the ground wishing we were up there than vice versa in a bad situation. |
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Seems to me that we should look at the most likely failure mode of an electronic/MIMS/whatever ADAHRS, which I suspect is probably a complete failure (which would show as a failed component/red X/etc. on the corresponding display). Second most likely might be a complete failure of a sensor in one axis, which perhaps would be caught by the EFIS or the ADAHRS and flagged (I dunno...maybe not, but it seems if a sensor is out and not providing data, the Kalman filter can't operate properly and find a solution?). Third, and probably least likely, is an *incorrect* reading from a sensor...which is what all the "tie-breaker" discussion has really centered on. So I'd be interested in real-world data on failure modes and likelihoods, and then one could do a proper FMEA to figure out how to mitigate those risks. Just saying "failure" is not specific enough. In the case of an incorrect attitude, I should be able to first see the difference between the two systems, then resolve it by comparing it to GPS track, airspeed, altimeter, ROC indicator, etc. Just as an example...sort of like how it has always been done in the case of a failed mechanical gyro or vacuum pump for a "traditional" AI, right? |
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If airspeed is unavailable, the SV manual says that GPS groundspeed is used as an attitude aid ("GPS Assist" is displayed). But with a partial blockage, I suppose that both of them would show the same incorrect value. Better install a 2nd pitot tube to avoid this SPF. :eek: |
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