If you have a look at FCOM BULLETINS No 11 FCB-FCB11 – IDLE FACTOR, I think this explains the workings of THR DES, as far as I can see it does not have this function on the 320, only the 330/340. If you can't find it in your own FCOMs I'll try to post a link later.
Last edited by macdo; 14th Jun 2012 at 11:54.