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Continous bank in ALTN law

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Continous bank in ALTN law

Old 8th Apr 2021, 13:57
  #1 (permalink)  
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Join Date: May 2020
Location: Netherlands
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Smile Continous bank in ALTN law

Hello everyone,

I am new here and the reason I am joining is that I found answers to many of my questions here already.

So now I am asking about an issue I came across to that I couldn't find an answer to so far.

So my question is that, on A320 when we are in a steady flight at FL100 and the aircraft changes to ALTN LAW (for example double ADR failure), is it normal that the a/c start banking slowly (0.5 deg/min) with no side stick input?
kshsim is offline  
Old 9th Apr 2021, 22:47
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Join Date: Oct 2003
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I know nothing about the A320, but seriously - 0.5 degrees per minute?? That is far more stable than random air motion would give you even if the aircraft is perfectly in trim, so it sounds pretty good to me.
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Old 12th Apr 2021, 13:15
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Join Date: May 2020
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Hi, thanks for your answer, yes the a/c is manually flown as double ADR failure, with no sidestick input. Well, it is not always 0.5 deg/min sometimes it will be faster, and when you plot the yaw history it looks really like a deviation and not an oscillatory behavior. With ADRs back to normal it starts oscillating around the newly reached back angle (which makes sense as the a/c will be kept in the desired bank angle less than 33 deg with no side stick input).
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Old 13th Apr 2021, 11:28
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kshsim, are you expecting bank angle hold in ALTN LAW? If it is rolling, use some rudder trim to induce enough sideslip to counter the residual rolling moment. Not elegant but there is no pilot activated lateral trim.
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Old 13th Apr 2021, 11:39
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Join Date: May 2020
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zzuf we are flying straight not in a bank and my question is that in a simulated environment (so silent air).

Is it normal that we have some bank when we go from normal to altn law? so start rolling after switching to altn law?
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Old 16th Apr 2021, 06:35
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Join Date: Jul 2007
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Remember that in Normal Law neutral Sidestick will command roll rate zero. That won’t maintain wings level per se but will oppose any tendency to roll.

in Alternate Law roll control is direct. So if you have any any residual rudder trim, even a tiny amount of asymmetric thrust, or the aircraft isn’t perfectly rigged it will have a tendency to gradually deviate over time.

you might get some better answers if it’s moved this to the “Tech Log” area of this forum.
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