Misbehaving yaw damper ?
 

It is the second time I encountered this issue on a 320 (-200), traveling as SLF, seated in the back. About half-way into the climb to cruise a very noticeable side-to side vibration developed, with the jerks strong enough to prevent me from typing on my laptop keyboard. The frequency was around 3-4Hz, perfectly regular, unlike the irregular jerks caused by normal yaw damper action. As soon as we reached cruise, it stopped in both cases and did not appear again during the remainder of the flight. I have informed the front row, in both cases they felt nothing but agreed the symptoms sound like the yaw damper.

Can anyone with experience on the 320 shed any light on the issue ?

I have encountered that several times in the 320, and after consulting engineering department, they came to the conclusion that it was cause by a misalignment of the rudder trim, which itself was caused by aligning the IRS while having flaps 1+F. They issued the recommendation to always align the IRS with Flaps 0.

Whenever that comes up during climb I disconnect the autopilot and 'tap" the rudder trim to the left for a brief moment, without applying any input to the sidestick. That causes the airplane to slightly move sideways, and the vibration to dissapear completely.

iggy Many thanks for the quick explanation.

Can't say I've ever encountered it (8+ years on the 320 family).

Was there any explanation as to why the Flap setting interferes with the IRS alignment?

More info here: https://www.pprune.org/tech-log/6092...flaps-1-a.html

Up front you cannot feel it, one needs to sit at the very rear. As posted above, encountered it twice in 20+ years, in both cases the crew were completely oblivious. Does not appear to be a common occurrence, but very noticeable when it happens.

Pardon my ignorance, apart from the very last post in the linked thread, there's no hint about problems with aligning the IR with F1. All about turning the ADRs OFF ...

What did I miss? Andrasz and you seem to be talking about another issue, many thanks.

Good point, are we talking IR or the ADR part anyway...