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AFS AHRS failed in IMC
Yesterday I was in solid IMC coming from PMP to RYY when my AFS 4500 AHRS quit for about 5 mins. It started tumbling like a failed gyro. Luckily the plane (RV-10) has 3 independent AHRS and 3 screens so it was really a non event. However, I did notice that my AFS pilot, which was in efis mode at he time, went down with it, so I had to hand fly the plane.
My question was that I thought the AFS autopilot(really a trutrak) was slaved to the GPS and not the AHRS. My other question was, if I had put the AFS pilot in AP mode rather than EFIS mode, would it have held the headings and altitudes. BTW, after about 5 mins of straight and level, the AHRS re erected itself and the flight home was uneventful( with the exception of dropping temps and having to descend to stay the heck out of the icy clouds) Ted Chipps N498EC |
In internal mode the auto pilot would not have been affected. In EFIS mode it is getting GPS Steering commands so if the EFIS goes crazy, so will the auto pilot. The AHRS failing would cause the AFS to send erroneous commands to the auto pilot to get things correct again.
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Did you notice if the failed EFIS still showed correct turn coordinator indications, or did everything fail? |
To expand a bit on Jesse's comments...
With the AFS EFIS driving the autopilot, the EFIS is telling the autopilot to "steer right" or "steer left" based on several variables such as ground track and heading. If the EFIS loses its ability to provide, for instance, good heading information because its AHARS has gone nuts, the EFIS will be sending incorrect steering info to the autopilot based on its incorrect heading information. The AFS autopilot is essentially a re-branded TruTrak unit which has internal solid state gyros as well as connections to pitot and static inputs. It's capable of flying the airplane totally on its own, independent of the EFIS. Notwithstanding the above, now would be a really good time to download the flight data and get it to AFS for analysis to figure out what went wrong with the AHARS. |
The AFS can compare AHARS and should be able to identify the one thats faulty.
I'm fairly sure that applies to the 4500 as well as the 5000 series. Did you have any idea why it happened? |
Afs tumbling
No idea why this happened
I did see it happen in VMC about 2 years ago but to re erect after about 3-4 min of equlibrating. I may have began taxiing while it was equlibrating on the ground, but not sure Your answers about the autopilot were what I expected, however, My first instinct was fly the airplane as they always say! With a crazy autopilot in IMC I instinctively disconnected and hand flew straight and level Only after it normalized did I re engage the AP in EFIS mode and all was fine, but the thought of using the internal mode only occurred to me after landing I was planning on going up today and pulling the circuit breaker on the screen and shutting it down to replicate the scenario in VMC, but weather had other plans. Flying is about learning! Thanks everyone! |
BTW to Bob Turner,
I don?t know if you fly a glass panel, but the ADAHRS is just one box that handles all the air data, attitude and heading reference, and that includes turn coordination, so yes the TC was failed as well. However, since this represents a single point of failure(catastrophiclly so), its is essential to have a backup or 2, which is precisely why I have three screens and three independent ADAHRS Which quite honestly, probably saved my and my daughters life yesterday! |
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Very pleased it worked out for you. |
This is one of the weak areas I see with many pilots who are now flying glass cockpits. A good BFR should simulate failures of the various pieces of equipment such that you know how to instinctively react when failures occur. And one should practice every once in a while on the ground. After all, we can't go flying all of the time.
Our airplanes are so much more automated than the ones most of us learned to fly in. But when the automation goes away, they can be a handful. Kudo's to Ted for flying the airplane. Vic |
Hey Vic,
Is there a way to quickly slave the AP to the other screen? |
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OR, switch the 3 wires to your GPS (430W, etc) and run the autopilot directly from the autopilot controls (you will lose some functions, like VOR tracking and heading tracking (but have ground course tracking)). This is what Vic was referring to in his last post. It's amazing how fast you forget how to run the autopilot off its own controls! I'm guilty here. |
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I think it would be easier and more effective to put the AP in AP mode and fly manually via the AP course knob. If you upgrade to the Vizion, you can simply hit the blue button to maintain current course and altitude until you can come up with a plan of attack to address the situation. |
Failure simulation
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I will try to respond to both questions:
There is no way to swap to the other EFIS. That's why dual AHRS are a must for IMC flight (in my opinion). It is quite easy to jsut hit the buttons on the A/P and fly it in ground track mode and manually fly the altitudes. It's one of the reasons I keep the A/P separate. I actually had to do this a couple of weeks ago. I engaged the A/P right after take-off and the vertical would not engage, only the lateral. First I disengaged to make sure it wasn't going to do something stupid, made sure the airplane was trimmed for what I wanted, then engaged the A/P. I saw the GS Flag, which meant there was no vertical guidance from the EFIS. For the rest of the day I just managed the vertical through the A/P front panel interface. At the time I didn't know if it could be the EFIS or the ARINC. I will chalk my reaction up to I fly a lot of solo cross countries and when I am sitting there bored I do play a bunch of what if scenarios. That's the answer to the second question posed about trying to simulate real world failures. Granted, they ALL can't be simulated (if you have your ARINC on a separate fuse/breaker, you can simulate some insidious things). However, you can spend time talking about what-ifs, and you'd be surprised what you can dream up when you are sitting there on Autopilot during a cross country flight. Even today, as I am getting ready to fly to Frederick, MD for a prebuy, with it being 16 degrees here and 11 there, I am thinking of cold weather scenarios as I go through the preflight planning. Being in Atlanta, it is rare to fly in these kind of temps. Vic |
Installed switch to change AP control
between my 5600T or direct from the G650 (TT Vizion 385) -- also have independent Dynon D10A for backup.
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The issue comes down to, do we need more regs to protect us from ourselves? As a cfii I get to give IPCs to pilots who have flown for years managing to get in 6 approaches every 6 months, but then they lapse. Some of them are extremely rusty on partial panel. At least one claimed it was not possible to fly under the hood without the autopilot. |
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You have the older Crossbow AHRS and it sounds like the AHRS or Crossbow Magnetometer had a problem. "My question was that I thought the AFS autopilot(really a trutrak) was slaved to the GPS and not the AHRS": If you were in EFIS Autopilot NAV mode the EFIS should be passing the ROLL steering commands from your external navigator directly to the Autopilot. In this mode I don't believe a failed AHRS would cause any problem with the AP. The EFIS only sends GPS Track, Desired Roll Angle, and Vertical Speed to the TruTrak. In EFIS Nav mode the external navigator is calculating the desired roll angle and the TruTrak is using it's internal AHRS for attitude. "if I had put the AFS pilot in AP mode rather than EFIS mode, would it have held the headings and altitudes" In AP mode the Trutrak is following the GPS track and vertical speed set on the Autopilot Controller. With our newer AF-5000 systems the ARINC, EMS, and ADAHRS are all on the Dynon SV-Network. You can see and change ADAHRS from any EFIS screen. Rob Hickman Advanced Flight Systems Inc. |
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