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Old 24th Jul 2013, 02:45   #1 (permalink)
 
Join Date: Oct 2010
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A320 Rudder Trim on short final

Hi.

Please tell me if there is any airbus recommendation for rudder trim on short final when in manual landing (All engines operative).

Usually during autopilot engaged, autopilot takes some rudder trim. When we make manual landing, and after disconnecting autopilot, should we neutralize rudder trim?? or should be still deflected??
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Old 24th Jul 2013, 02:57   #2 (permalink)
 
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If you are having to push on a pedal to keep the aircraft straight, trim until you no longer have to push the pedal. That's what the trim is for.

Last edited by ahramin; 24th Jul 2013 at 02:58.
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Old 24th Jul 2013, 05:12   #3 (permalink)
 
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krbys
I have not found any Airbus reccommendation for that but by common sense if AP has trimmed the rudder you need that and should be left as it is till you land.
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Old 24th Jul 2013, 12:00   #4 (permalink)
 
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There is no need to zero the ruder trim when landing on two engines. When on one engine get your PNF to zero the rudder trim in the flare for you.
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Old 24th Jul 2013, 15:04   #5 (permalink)
 
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I looked for it in our FCTM and found no suggestions in it for rudder trim use with all engines operative. So as ahramin said in his first reply: "If you are having to push on a pedal to keep the aircraft straight, trim until you no longer have to push the pedal. That's what the trim is for." The topic could have been closed at that point.

On one engine our FCTM says: "To make the landing run easier, the rudder trim can be reset to zero in the later stages of the approach. On pressing the rudder trim reset button, the trim is removed and the pilot should anticipate the increased rudder force required. With rudder trim at zero, the neutral rudder pedal position corresponds to zero rudder and zero nose wheel deflection."

Personally I do not reset the rudder trim to zero when disconnecting the A/P on single engine scenario in the sim. Most of my colleagues however do it somewhere on final! Airbus does not tell you you should do it, but suggest that you CAN do it. Next time in the sim, time permitting, try it and see what you prefer.

Fly3 suggest to reset it to zero during the flare. I admit I haven't tried that (not going to either), but I would think that is not very good advice. Better do it somewhere on final, rather then having to adjust to a changing rudder trim when you're just about to touch down!
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Old 25th Jul 2013, 02:33   #6 (permalink)
 
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Zero-ing the trim in the flare is not a problem at all as you should be looking out and just keeping the aircraft pointing straight down the runway. If you have drift due to crosswind resetting just gets "lost" as you squeeze the rudder to align the aircraft. This was the technique taught by an Airbus test pilot during my training in Toulouse.
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Old 25th Jul 2013, 05:58   #7 (permalink)
 
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@fly3
Well, perhaps I will try it next time I get in the sim.
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Old 25th Jul 2013, 13:40   #8 (permalink)
 
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sabenaboy
What Fly3 has suggested is taught by most instructors. However every airline
has its own height during approach they suggest to zero rudder trim. You feel zeroing rudder trim during flare will cause yaw. It doesn't cause that much because the thrust which is causing the yaw is brought to idle. On the other hand holding on to the trim during flare (not zeroing) as you do will cause yaw to the other side and you will have to counter that during landing roll.This can be aggravated by Xwind from the that side. I have not seen any document suggesting your method. That does not mean you cannot land without zeroing rudder. You can fly the whole approach manually without triming holding the rudder but in case of incapacitation the PNF will have a surprise.
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Old 26th Jul 2013, 15:23   #9 (permalink)
 
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You could just fly the airplane (an unusual concept nowadays, I know). If it takes pedal pressure to keep coordinated, trim accordingly. If not, leave it be.
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Old 27th Jul 2013, 03:53   #10 (permalink)
 
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Some people seem to be missing the point of zeroing the rudder trim. It is done to re-establish full and equal nose wheel steering both ways using the rudder during the landing roll. If you land with out doing this there is a possibility that you will run out of authority steering to the side that has the trim.
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Old 27th Jul 2013, 08:27   #11 (permalink)
 
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Quote:
Originally Posted by fly3
If you land with out doing this there is a possibility that you will run out of authority steering to the side that has the trim
I always thought that the rudder trim on the A320 only influenced an artificial feel unit and had no influence on the maximum rudder deflection or nosewheel steering limit! If so, the pilot would perhaps need to use more force, but full rudder travel would still be available. That would explain why the FCTM uses the wording "the rudder trim can be reset" during OEI approach instead of saying that it should be reset to zero.

So I went looking for clues in the FCOM to back up my point of view. This is what I found: (make sure to read the bold print)
Quote:
Originally Posted by FCOM DSC 27-10-20
RUDDER TRIM
The two electric motors that position the artificial feel unit also trim the rudder. In normal operation, motor N 1 (controlled by FAC1), drives the trim, and FAC2 with motor N 2 remains synchronized as a backup.
In manual flight, the pilot can apply rudder trim with the rotary RUD TRIM switch on the pedestal.
- Maximum deflection is 20 .
- Rudder trim speed is 1 /s.
- In addition to limitation by the TLU, if rudder trim is applied, maximum rudder deflection may be reduced in the opposite direction.
The pilot can use a button on the RUD TRIM panel to reset the rudder trim to zero.
So this confirms that rudder trim works through an artificial feel unit, but at the same time says that max. rudder deflection may be reduced.

So here's what I dislike about the A320 FCOM: the lack of correct clear information! Surely one would think that rudder trim should be reset if rudder deflection is affected. Why use the word "may" in the FCOM? It either does reduce rudder deflection in certain conditions or it doesn't! I still think that it doesn't and I'm tempted to try it on my next flight: after engine start, put a significant amount of rudder trim in (10 or so) and check the F/CTL page for full rudder deflection when testing it. (I won't forget to put the trim to neutral again before taxi. )

But, anyway, even if my numerous sim sessions over the last 11+ years, and instructors' feedback have never demonstrated the necessity to zero the rudder trim before OEI ldg, I will be doing it in the future just to be on the safe side.

Thanks for the input, Fly3 and vilas.

Last edited by Jetdriver; 2nd Aug 2013 at 02:19.
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Old 1st Aug 2013, 23:19   #12 (permalink)
 
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Quote:
If it takes pedal pressure to keep coordinated, trim accordingly. If not, leave it be.
I suppose we are all trimming out the beta target, in manual and wings, verily, level and then applying trim to the opposite to the dead leg . . ? i.e to the live engine side

why mess with it other than that?

Last edited by Natstrackalpha; 1st Aug 2013 at 23:20.
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Old 2nd Aug 2013, 00:17   #13 (permalink)
 
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A320 Rudder Trim on short final

Would you land OEI with max crosswind? I am a A320 TRE, I don't judge when people do or don't. But personally I don't bother..
Happy landings
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Old 2nd Aug 2013, 02:21   #14 (permalink)
 
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Quote:
Originally Posted by sabenaboy View Post
So here's what I dislike about the A320 FCOM: the lack of correct clear information! Surely one would think that rudder trim should be reset if rudder deflection is affected. Why use the word "may" in the FCOM? It either does reduce rudder deflection in certain conditions or it doesn't!
From what I've read, FCOMs are a bugbear - not least because the procedure in writing them was to write them first in French, then have them translated into English (among other languages). This makes sense in terms of having them all say exactly the same thing no matter what language they are read in, but it definitely results in some curious use of language from the point of view of a native English speaker.

In this case however, I suspect there is method behind the choice of words. Technical writing exists in a state that is balanced on the edge of conciseness versus accuracy. If it is stated that something "will" have an effect, then it implies that all failure modes have been tested and behaviour has been shown to be constant. The use of "may" allows for the existence of failure modes that were not covered in the design and testing regime.
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Old 2nd Aug 2013, 03:46   #15 (permalink)
 
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I am so glad I don't fly an Airbus. In the Boeing you just keep it pointed and land the airplane. We don't need an autopilot to land and if we are coupled up we don't need instructions on how to land it once disconnected because we learned that in basic training. Just land as any normal pilot would do. Where did you learn to fly?
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Old 2nd Aug 2013, 07:21   #16 (permalink)
 
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bubbers44
It is as simple or even simpler in Airbus. Sabinaboy had some misunderstanding thats all. It holds the pitch and bank what could be simpler.
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