Originally Posted by
DaveReidUK
The tailplane (in the days before we called them horizontal stabilizers) was moved by 3 hydraulic jacks in response to pitch (or a/p) inputs. The "elevator" wasn't really an elevator at all, it was a massive geared tab moved by a simple mechanical linkage to the stab. I suspect what you encountered was a failure of that linkage, which would indeed allow the tab to float freely.
Yes the "all-flying" tailplane, like the other primary controls, was driven by three hydraulic jacke, one for each hydraulic system. Our logic for the triplex system arrangements was that they were part of the way we met the reliability target which led to certification of autoland. As DaveReidUK wrote, the thing that looks like an elevator is a geared tab so can we agree on these matters and debate something else?
PS I wrote "our" because I worked at de Havilland at the time, not because I designed the system.