I am afraid to ask, but what does a 'Yaw string' look like? Is it like a plumb line? And what would I be looking for? I can see that if the aircraft was banked the line would be off centre, but would there be a displacement if there were yaw? I suppose there would be if the IRS is sensing it, and displaying it on the PDU.
I always have to trim left rudder as I accelerate, and there it remains for the flight, but it needs to be reduced in the descent eventhough speed is still high. So am I experiencing asymmetric thrust? FADEC controlled engines, N1 matched. Pretty new airframe too.