SkyView autopilot failure modes information
- Thread starter Solana
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DBRV10
Active Member
The AP simply follows the FD, so whatever mode the FD is in is what will be affected. Obviously static affects everything. IAS, well there is a backup to that for the attitude algorithms called GPS assist. Your lateral modes would be fine. Pitch is a bit dependent.
What are you planning Rick? ;-)
What are you planning Rick? ;-)
Thanks David! So is the autopilot attitude-based (not rate-based)?
Since attitude is augmented with airspeed, then pitot or static loss would cause the GPS-assist to kick in. In the ridiculously unlikely scenario of you losing either pitot or static, as well as your GPS signal, you would lose attitude and therefore flight director?
if you lose static, what happens to vertical nav?
if you lose pitot, what happens to the constraints for highest and lowest air speeds? Do they use ground speed?
lots of questions! Probably have too much time on my hands due to COVID!
Marc_J._Zeitlin
Active Member
Your questions about failure modes are good ones, and it would be really nice if there were documentation of them. A friend who has a full G3X system in his COZY MKIV had the ESP-X low speed protection kick in on him when his pitot iced up and he lost pitot (exactly what you posit here) and the plane dove toward the ground, trying to gain airspeed. Obviously, he had to turn the system off and hand fly the approach in busy LA airspace while in the clag. Would have been OK if it had been expected, but the plane tried to kill him, theoretically while thinking it was saving him. Obviously Garmin screwed up on failure modes.
It would be good to know what the Dynon system does with various input failures, or combinations of failures.
DBRV10
Active Member
Too many undefined questions. What if you lose static? Meaning the two ports are plugged simultaneously, or the tube falls off in the tail cone, or the ADAHRS has a component failure? The results would vary from no much to a reported fault. Do you have a 200&201?
You could go for days, years even on this.
You could go for days, years even on this.
Marc_J._Zeitlin
Active Member
Does the fact that it's complicated mean that we shouldn't ask the questions, or that Dynon has no responsibility to tell their users what the failure modes of the system are?
I performed the SSA/FHA Fault Tree analysis on the SS2/WK2/RM2 spacecraft, aircraft and rocket motor before I took over the RM2 development effort for three years. This is EXACTLY the process used to determine failure modes and effects. There are a bunch of sensors that feed the Skyview ADAHRS system and display. It is important to know what happens if a sensor stops working, works intermittently, or works incorrectly, and these include wiring or connector failures, as well as electrical failures and EMI/RFI induces failures.
I'd suggest that if Dynon were to respond to this thread, they could respond with a list of all sensors, both internal and external to the EFIS/ADAHRS, along with the consequence of a specific sensor's failure, either total, partial, or incorrect. And in fact, the effects of failures of subcomponents of the EFIS would also be useful to know.
One would HOPE that the result would be that:
- all of these failure effects are known, at least internally to Dynon
- all of the effects of the failures are neither Catastrophic or Hazardous, as defined by the FAA, but at worst Major
- since the system is STC'd for TC'd aircraft, it has been developed with DO-178C (software) and DO-254 (hardware) processes, in which case they'd HAVE to have done the above analyses
My $0.02.
airguy
Well-Known Member
Part 91 much?
Marc_J._Zeitlin
Active Member
Meaning what? That in Part 91 ops, reliability and failure modes are unimportant? I understand that performance levels are different for Part 91 ops, and that DO-178C and DO-254 standards, as well as TSO's, even if not absolutely required, might be followed because they're good practice. But even if they're not, it's good practice to evaluate and understand failure modes.
Why is it a bad idea to ask about them, so that the pilot can know what to expect in the case of a failure, and understand what they're seeing from the standpoint of what it might imply about what failed?
So I agree that I am not looking for the complex information that David describes. That is too complex to be useful in flying the plane.
By way of trying to describe what the output might look like, let me start with the fact that the PFD already has logic that determines when it puts up a red X in response to failures like those mentioned by David. And let’s assume that the autopilot is attitude-based and is driven by the flight director. Then my questions might be reduced to what does the autopilot do when the airspeed has a red X. Same question for altitude, attitude, heading, course, etc.
Marc’s story of the G3X pitot loss is something I hadn’t thought of, but certainly underscores the value of knowing what could happen so you can quickly deal with it without going into brain meltdown.
It could help hen designing your plane’s system too. On a very simple level, the fact that the SkyView screen is part of the autopilot, so that you lose the autopilot if you lose a single screen, is why I have dual screens.
Dynon might have just the right level of information!
Rick
By way of trying to describe what the output might look like, let me start with the fact that the PFD already has logic that determines when it puts up a red X in response to failures like those mentioned by David. And let’s assume that the autopilot is attitude-based and is driven by the flight director. Then my questions might be reduced to what does the autopilot do when the airspeed has a red X. Same question for altitude, attitude, heading, course, etc.
Marc’s story of the G3X pitot loss is something I hadn’t thought of, but certainly underscores the value of knowing what could happen so you can quickly deal with it without going into brain meltdown.
It could help hen designing your plane’s system too. On a very simple level, the fact that the SkyView screen is part of the autopilot, so that you lose the autopilot if you lose a single screen, is why I have dual screens.
Dynon might have just the right level of information!
Rick
DBRV10
Active Member
Marc,
My point is, Rick asked a series of very open ended questions.......and that could lead to more and more and more^6. This is an internet forum, I do not work for Dynon and I only have some of the answers and could only guess at the rest. Nobody is paying me for days worth of responses and "what if" questions. The internet is littered with debates like this. I am not playing that game.
Of course in Experimental aviation, in VMC, you could easily enough test all the manner of failure modes yourself and have a lot of fun doing so.
My point is, Rick asked a series of very open ended questions.......and that could lead to more and more and more^6. This is an internet forum, I do not work for Dynon and I only have some of the answers and could only guess at the rest. Nobody is paying me for days worth of responses and "what if" questions. The internet is littered with debates like this. I am not playing that game.
Of course in Experimental aviation, in VMC, you could easily enough test all the manner of failure modes yourself and have a lot of fun doing so.
Marc_J._Zeitlin
Active Member
I guess I made the assumption that since Dynon reads these fora and responds on occasion, that THEY were who he was addressing his questions to. Not to you, not to me, and not to anyone that didn't know the answer. Why do you think that you were the one that he was asking, in particular? I agree - you have no obligation to respond to anyone about anything. But I'd suggest that Dynon does
. That's certainly who _I_ was posing my questions to - not to you, or any other non-Dynon employee.airguy
Well-Known Member
I'm guessing Dynon is smart enough not to play the "what if" game also. Read the manual, read the specs, draw your own conclusions and test your individual installation.
DBRV10
Active Member
I guess I made the assumption that since Dynon reads these fora and responds on occasion, that THEY were who he was addressing his questions to. Not to you, not to me, and not to anyone that didn't know the answer. Why do you think that you were the one that he was asking, in particular? I agree - you have no obligation to respond to anyone about anything. But I'd suggest that Dynon does
With all due respect, this is a forum for Dynon users and one where the company has zero obligation to comment. Any open ended questions are open to the floor, and maybe I missed something but so far I have not seen anyone address Dynon directly. I would also suggest the best way to do that is in writing and on paper in the post.
I concur with airguy and his assessment.
I do suggest you test these failure modes that interest you for yourself. You will have a blast.
I would like to know as well.... particularly if the pitot gets covered in ice. I saw a video of an RV10 with a G3X with a frozen pitot and was really surprised at the chaos in the cockpit. The stall warning was alerting continuously and the auto pilot disengaged.
I don't look forward to a failure mode like this, but would like to train for it.... if that is the way skyview works.
Dynon... Please share with us what you know with regards to this failure mode and what to expect. Thanks.
I don't look forward to a failure mode like this, but would like to train for it.... if that is the way skyview works.
Dynon... Please share with us what you know with regards to this failure mode and what to expect. Thanks.
While some static system problems create issues for attitude, hopefully anyone flying IFR will have an independent backup to use.
I am more concerned about auto-trim failures that have the servos fighting the auto-trim. I highly recommend leaving the trim messaging on so that you know when system is calling for trim, vs where the trim is positioned.
SkyView's autopilot doesn't disconnect as aggressively as some others do. It will keep trying to fly the airplane. That said, some comments on pitot/static issues:
In the event of ice obstructing the pitot tube the airspeed indicator may read erroneously low. If the autopilot is already engaged, a very low airspeed reading will cause the low-speed envelope protection feature to activate. This feature is designed to lower the nose at low speeds to prevent a stall. We of course recommend activating pitot heat prior to flight in icing conditions. In the event of airspeed malfunction, disconnect the autopilot and fly manually.
This is more intended for the Dynon Certified installs, but the AFMS for the system has some emergency procedures in place for AP scenarios too: https://www.dynoncertified.com/down...iew_HDX_Airplane_Flight_Manual_Supplement.pdf
In the event of ice obstructing the pitot tube the airspeed indicator may read erroneously low. If the autopilot is already engaged, a very low airspeed reading will cause the low-speed envelope protection feature to activate. This feature is designed to lower the nose at low speeds to prevent a stall. We of course recommend activating pitot heat prior to flight in icing conditions. In the event of airspeed malfunction, disconnect the autopilot and fly manually.
This is more intended for the Dynon Certified installs, but the AFMS for the system has some emergency procedures in place for AP scenarios too: https://www.dynoncertified.com/down...iew_HDX_Airplane_Flight_Manual_Supplement.pdf