System known as Active control had as an working principle an installation of accelerometers in fuselage and wingtips, which detected vertical accelerations and by so deflect the ailerons in order to reduce wing bending due to a redistribution of lift forces, making until today the smoothest aircraft to ride on. All this was accomplished in a automatic way, without interference of pilots.
ACS was invented for the -500 so they could extend the span without beefing up the wing. This gave the plane greater range. I never rode on a -500, so don't know about its ride, but Lockheed has always been known for a very stiff wing and more abrupt ride. Stiff wings seem more prone to crack, like the C-5, C-130 and Electra.
It was the first wide-body aircraft to have an digital auto-pilot, been this one, one of the most accurate ever built, instead of the old analog systems.
The original L-1011 AP was analog. Digital AP was developed in the late 1970s for the -500 series. Even the analog AP was good for Cat IIIc. The digital was dual-dual like the original. Boeing chose the simpler triplex for the 767 and all subsequent planes.
GB