The Flap Trim Compensation (FTC) system fitted only to the -300 variants will lower the trim (nose down) by approx. 1 unit when the flaps are extend from 0 to 18 degrees, and increase the trim (nose up) when retracting from 18 to 0 degrees. That's designed to reduce the control inputs required to counteract the ballooning affect. So on approach you'd get automatic nose down trim when extending the first stage of flap, however note that the system is only active with the autopilot off and is also cancelled if the trim switches are moved.
Why is the pitch trim moving automatically when extending or retracting the flaps on the -300 variant?
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