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Integrated Autopilot Failure Mode(s)

Toobuilder

Well Known Member
Hello all,

I?ve followed/searched the numerous threads concerning ?redundancy/backups/single point failure/etc.? and have not found the specific answer I?m looking for. It?s probably buried in there somewhere amongst the mountains of tangents this type of thread generates, so I?m going to try cut to the quick in this one.

Concerning integrated autopilot function in a single AHARS Skyview or G3x suite ?

In the unlikely event that the screen goes blank, will the autopilot continue to function?

The basis of my question concerns the tradeoff for capability offered by fully integrated system vs. the perceived safety aspect of a standalone autoflight system. For example, if the GRT screens die in the -8 at the same time I?m somehow in IMC, at least the TT will keep the wings level, maintain altitude, and can drive me somewhere else. Not sure I could do that with a fully integrated suite like I?m planning for my next airplane.
 
In the unlikely event that the screen goes blank, will the autopilot continue to function?

It depends on the reason the screen went blank, and which integrated AP you are using. They all have different failure modes and resistance to component failures.
 
I have wondered this also.

To be specific, what if you have a GRT HXr single screen with remote radios and transponder and the GRT AP servos, and the screen goes blank or the EFIS dies completely?
1. Do you have AP still?
2. Do you have radios or transponder?

My plan is to always have a independent backup that will let me know the basics, but it sure would be nice to have the AP still functioning if it is bumpy and I am trying to sort things out.

And to compare, what about AFS, Garmin, or Dynon Skyview?
 
Well,

I've run through the "glass with steam backup" and "redundancy" debates in my head and for me it comes down to something as simple as "not die" if the glass goes dark. I don't need to continue the approach to land if the primary display goes TU, I'm satisfied simply with a method to keep the wings level. To me, the best bang for the buck is to jump on already existing equipment as my "not die" plan - the autopilot.

So I guess the question is not quite as simple as I thought.
 
AS far as the G3X goes....

The G3X autopilot and servos need a functioning screen and a functioning AHRS to operate without a GMC305 in the mix. If you have multiple screens, you have screen redundancy and if you have multiple AHRS units, you have AHRS redundancy. (common mode failures excluded)

If you have a GMC305 in the mix, the G3X autopilot and servos can operate in certain modes without a working screen. They still require a working AHRS and in this case a working GMC305.

With the 3rd party autopilots like the TT GX Pilot, if you lose the G3X system, you are left with the native modes supported by the AP. They do have built in independent gyro's. Be aware however that these gyro's are not capable of full 360? of pitch and roll and can saturate/tumble if the limits of pitch, roll, or rate are exceeded. They may or may not be able to recover in flight if they do saturate/get tumbled.
 
This was one of my big concerns when designing my panel 10 years ago, when the Garmin 430 was the most popular radio for my desired level of capability. I was not comfortable with the notion that if I spent all my money on one integrated radio rather than 2 separate, cheaper but non-integrated radios, if the screen went out, I was out of luck.

Integration is great but you have identified one of the downsides...single point failure.

I think it's a philosophical decision, made easier with copious amounts of $$$$:D
 
One major advantage of the integrated EFIS and AP is that the AP knows what the plane is doing, its limiting speeds, etc.

Thus, if you get into a death spiral, or worse, and your speeds are still in the green, many of the integrated systems will let you engage the AP function and fly safely away. Independent systems simply can't do that.

If you go with an integrated system, regardless of who the manufacture is, I strongly recommend a Dynon D1 Pocket Panel. I had the honor of being a beta tester on this unit and I can't say enough about it and its capabilities. Between that and a handheld GPS, you should be able to keep your plane upright long enough to find a safe place to land.
 
Thanks Brian for the insght on the Garmin system.

So what are the circumstances that can take down both the pilot interface (display) AND the autopilot function of a Skyview; and conversely, is there a different set of circumstances that can leave one or the other functional?
 
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My thought is that if the screen is dark, lets say a failure mode that only appears to affect the display not the functionality of the EFIS/auto-pilot, then its still "all dead to me".

If the screen is dark how can you know what your auto pilot is doing or is getting ready to do? What happens if the thing comes back alive again?

If my EFIS goes dark, I think the second or third thing on my list is to power down the A/P servos.
 
The issue only matters if you are IFR.

If VFR and the screen goes U/S and you have nothing else, fly the plane. You do not need any bit of information contained on a G3X or sky view to effect a safe outcome.

In fact you do not need anything. Turn your Master Switch off one day and try it.

If you are IFR, having just one panel with one source of power to the bus and having two screens but on the same breaker, is just plain and simple silly.

I had a A/P failure due to a shear screw breaking in turbulence. In fact twice now, and one time it was about 45 minutes of bumpy IMC, the other was 2.5 hours of constant bumpy IMC. Had the primary screen failed and that took out my A/P it still would have been the same result. I kept on flying by hand on the EFIS.

I am not saying do not know your systems, even VFR it pays to know as much as you can, but so long as you do not sweat it.
 
...If you are IFR, having just one panel with one source of power to the bus and having two screens but on the same breaker, is just plain and simple silly...

...But it does happen. No, it's not a good plan and I would never do it intentionally, but sometimes people find themselves in the soup with limited equipment. My query concerns just that unlikely event.

So it sounds like it really comes down to the value of an integrated system vs. the redundancy of a stand alone AP. Hmmmm....

And, yes, I am a big advocate of flying with eyes out. I would have no issue taking off and flying the -8 on a 400+ mile VFR x country with the screens completely dark (if I had to).
 
You raise a good point, if IFR. After all that is the only reason for winding up in the soup. Nobody should find themselves in cloud by mistake. The R in VFR is RULES and if we stick to the rules for the flight system, there is never a problem. Anyway that is not the argument.

If flying IFR with one EFIS and an integrated AP, well you have nothing. :eek:

So in the old six pack you had an electric turn co-ordinator and that along with a DG and a compass and VSI and altimeter, is quite fine to fly on. But an EFIS is a one shot.

So if IFR, you need to have two EFIS or one EFIS and another AI of some sort.

The Dynon D1 is an excellent example.

Back to your original post, if you are planning a new panel, and it is VFR only operations, you do not need to worry about a single EFIS and integrated A/P.

If you want it to be IFR, it should have two screens, supplied by two separate breakers. Each screen should have a separate ADAHRS and the A/P can be slaved off one of the systems.

Electrically you need back up power either by built in batteries or two batteries or alternators and each power source needs its own separate and selectable dedicated path to the bus.

If you are only ever going to be a VFR pilot, for the once in a lifetime moment of stupidity, risk the chance of a screen failure and save the money. Spend that on motels if the weather is bad. Its more fun that way.

Hope that is helpful.
 
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