L1011 DLC
"reduces longitudinal scatter" ie the a/c touches down in the same area on the runway when coupled to an apropriate ILS. as said the spoilers move to a null 9 degrees position and operate up and down from there. This results in a stable approach attitude with elevator inputs controling rate of descent. It works very well, having completed 3 auto lands this week all were on the centerline 1000' from the threshold with about 1-200fpm sink on touchdown. Very smooooth.