Netralising Rudder Trim

[HERC]

Hi

Can some one please explain the reason for putting the rudder trim to neutral short of landing during an engine out approach on A320.

In my understanding, it is to avoid directional control problems after landing. While the aircraft is decelerating rudder loses its effectiveness and directional control through the rudder pedals operating the nosewheel steering may not be sufficient to stay on the runway. Moreover using the nose wheel steering tiller is not recommended till the aircraft speed reduces to a decent fast taxi speed.

Thanks

[TonyDavis]

As the power on the live engine is reduced, the rudder will have be moved to compensate and keep the aircraft straight. I have tried both centring the trim at about 200 feet and leaving it alone, seems to not make much difference either way. I know some operators reccomend it and some dont. Best do as your company says and then you dont get in trouble !!

Waiting to be shot down :E

[dream747]

With respect to the FCTM reference as quoted earlier, is the nose wheel centered with the rudder trimmed outside of 0?

[Endeavour]

is the nose wheel centered with the rudder trimmed outside of 0?

No, the nose wheel will be offset by a proportionate amount.

[Green Guard]

for 2 reasons:
1. you will have to reduce power to land, (so needing less rudder) you would have to use opposite one
2. after landing you would have to use more opposite rudder, and if you use reverse you might not even have enough rudder to push

[flyingchanges]

I would prefer to push in some opposite rudder in the flare vs being way out of trim for a go around.

You will not run out of rudder because of the trim setting. Every large twin I have been trained on has plenty of rudder authority in full reverse down to low speed.

Trim has no bearing on nose wheel position, rudder pedal position has bearing on nose wheel position. Most jets only have 6-7 degrees of nose wheel steering via the pedals anyway.

[dream747]

Do I have the correct understanding then to say that the purpose for resetting the rudder trim to 0 during the after start flow is to ensure the neutral rudder position corresponds to zero rudder and centered nose wheel? Cheers.

[Fursty Ferret]

Trim has no bearing on nose wheel position, rudder pedal position has bearing on nose wheel position. Most jets only have 6-7 degrees of nose wheel steering via the pedals anyway.

Not so, on the A320 rudder trim is a useful technique for taxiing in a straight line with a wonky aircraft. I ask for the trim to be zeroed on short finals - hasn't been commented on yet.

[rudderrudderrat]

Not so, on the A320 rudder trim is a useful technique for taxiing in a straight line with a wonky aircraft.
At what stage do you ask for it to be zeroed before Take Off?

[flyingchanges]

USAIR 5050 all over again...

[Fursty Ferret]

Before pushing the TO Config button. Ahem. It's buried in the FCOM somewhere as an accepted technique.

[rudderrudderrat]

Hi Fursty Ferret,
It's buried in the FCOM somewhere as an accepted technique.
Never seen it and never done it on any previous aircraft type.

[Meikleour]

rudderrudderrat (http://www.pprune.org/members/313106-rudderrudderrat): Furst Ferret is correct! It was a procedure designed to help maintainence rig the nosewheel steering correctly. IIRC trim could be applied when taxying in a straight line, up to a maximum amount and this was noted for the engineers.
The procedure called for the trim to be zeroed prior to take-off. There were limits on how much left/right trim could be used and still considered normal.

[rudderrudderrat]

Hi Meikleour,

Thanks very much for the info.
Please could you give the FCOM ref for that procedure.

[Meikleour]

rudderrudderrat: A330 FCOM3.04.32p5/6 OPERATION WITH NOSEWHEEL STEERING OFFSET

The tolerance was +-0.5o NWS offset = 2.5o rudder trim to taxi straight.
Outside that range the limit was 4 - 10 degrees to use the procedure and the trim had to be reset to zero prior to take-off.

PS I have never seen this procedure on the A320

[rudderrudderrat]

Thanks Meikleour,

@ Fursty Ferret.
I stand corrected for A330/340.
But where have you found that procedure written for A320?

[sabenaboy]

But where have you found that procedure written for A320?

It's in the FCOM PRO-SUP-32: OPERATION WITH NOSEWHEEL STEERING OFFSET
"The tolerance required by maintenance guidelines (± 0.5 ° NWS offset, corresponding to the ± 3 ° rudder trim necessary to taxi straight) remains valid.
Operating the aircraft outside the maintenance tolerance is possible by using the applicable procedure. However, in such cases, the flight crew must accurately and systematically make logbook entries (indicating the rudder trim input value to taxi straight) to ensure that maintenance can take corrective action within the applicable timeframe. When using rudder trim to taxi straight for NWS offset identification, takeoff must only be performed after a rudder trim reset."

[rudderrudderrat]

Thanks sabenaboy.

And I always thought it was "wonky" because of single engine taxi.