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During taxi / pre-take off I see a lot of commercial airliners test the deflections of their various control surfaces like the rudder, ailerons etc.

What's the feedback received in this operation i.e. The pilots themselves cannot visually verify the full deflections achieved on command, right? Unlike on (say) a carrier etc where there's a spotter on the ground to confirm.

Just curious, what is the failure mode to be revealed in this sort of test. Is there some sort of internal avionics indicator that would tell the flight crew if the control surface was not reacting to the inputs as expected?

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According to this PDF from Airbus (see section "The importance of the pre-flight, flight controls check"), the PF (pilot flying) moves the sidestick around in a defined manner while the PNF (pilot not flying) watches the ECAM F/CTL (flight control) page and calls out "full up", "full down", etc. (Actually the procedure is described in the A330 SOP but the linked document explains it in a comprehensible fashion.)

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Source

The ECAM F/CTL page displays the actual position of the control surfaces. This video from Captain Joe explains the behaviour of the sidestick in an Airbus and shows how the control surfaces can be checked on the ECAM F/CTL page (from approx. 1:40 to 2:15).

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  • $\begingroup$ Interesting! Somehow I never noticed this set of calls, "full up" "fell left" etc. in any of the flight videos I saw! Thanks for this explanation. $\endgroup$ – curious_cat Aug 19 at 5:24
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    $\begingroup$ @curious_cat You are welcome. Some of the call outs can be heard in this video from around 6:50 to approximately 7:15. It also shows the ECAM displaying the flight control's positions. $\endgroup$ – PerlDuck Aug 19 at 15:08

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