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Does the A320's Trimmable Horizontal Stabilizer (THS) automatically reset after landing? If so, is there any condition where it doesn't? And what about the rudder trim?

I'm asking because I'm studying from an old FCOM I found online and it doesn't state that any of those automatically reset but there are two questions in SmartCockpit that say otherwise (i.e. that both the THS and rudder trim reset after landing).

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  • $\begingroup$ THS - Trimmable Horizontal Stabilizer $\endgroup$
    – Pilothead
    Commented Jul 2, 2018 at 19:58

1 Answer 1

Reset to default
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If the quiz you saw is the same as this one, then please double-check it, as the one I linked has 'THS only' as the correct answer...

Q 31: Which of the following will automatically reset after landing?
A: THS.
B: Rudder trim.
C: Both are correct.

... which is more inline with the manual.

THS -- yes

The THS resets to 0° after being on the ground for +5 seconds and with the pitch attitude less than +2.5°. This is when the pitch law reverts to 'ground mode'.

Ground mode is a direct relationship between sidestick deflection and elevator deflection, without auto trim.
It automatically sets the trimmable horizontal stabilizer (THS) at 0 ° (inside the green band).

(A320 FCOM)

Also see: Why is it not recommended to hold the nose up on the A320 after touchdown?

Rudder -- no

There is no similar 'ground mode' for the rudder, and the manual does not mention an automatic rudder trim reset as far as I've checked.* I doubt one exists because in an engine-out landing, such reset would catch the pilot off balance. (The SOP calls for 5° trim towards the working engine when landing with an engine out.)

The SOP also calls for checking the rudder trim is zero after start, and resetting it if it is not.

* The manuals do not always tell the full story as Captain Sullenberger learned, so it goes without saying to not use the internet for flight.

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    $\begingroup$ It's coming back to 0deg +- .5 deg in Normal Law only. $\endgroup$
    – Chris Lau
    Commented Jul 4, 2018 at 14:48
  • $\begingroup$ What happens if the resting pitch attitude is greater than +2.5° (for instance, when landing on a [relatively-]steeply-sloping runway)? $\endgroup$
    – Vikki
    Commented Jun 6, 2019 at 3:19
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    $\begingroup$ @Sean: That's steep! And I don't know. But the question that comes to mind is what maximum slope is recommended? For the typical 45 m wide runway (code 4), it's 1.25% for any portion, or 0.56° (ICAO Annex 14). For super special ops, the airline can ask for a software change I suppose :) $\endgroup$
    – user14897
    Commented Jun 6, 2019 at 14:51

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