Originally Posted by
SASless
It seems we are seeing these events in more than one Make and Model of helicopter....and as in the current event the symptoms seen dramatic and persistent rather than just one stroke and in one direction.
If it was an AFCS problem....Pilot input by use of the Tail Rotor Pedals should have overridden the AFCS Input and should have ended with the turning the AFCS to OFF.
Has the design of modern day AFCS systems given the AFCS the ability to match or exceed a Pilot Input using the Pedals?
Not having a Sperry Helipilot AFCS Manual at hand....memory tells me the AFCS only had something like a 20% authority and was easily overridden by flight control input.
If the installed AFCS system is similar to that....it would suggest it is not the AFCS in the current event in OZ. (at least in my thinking).
I would think it was hydraulic system related rather than AFCS.....again if my thinking is appropriate for the installed AFCS on the aircraft in OZ.
The description of the event shows a really "interesting" ride on that Roof Top Pad which lasted some period of time.
I do have the SHZ-109 manuals but unhelpfully they only say plus or minus 5mm of travel not percentage. In any case it's small. In the AW119 RFM it does show a trim actuator in yaw which would have full authority but is slow acting. However, in the Bell 429 case it wasn't a malfunction of the actuators "running away", it was more a mode of the AFCS commanding (incorrectly) full travel. In that case simply moving the pedals would not correct the problem - they had to be put in exactly the right place (the detent) or the trim release depressed. So here in the AW119 that could happen but I suspect not as in my experience of AW109 AFCS it is not active during start so wouldn't be commanding anything. My money on the servo.