1.   The ABS computer is integral with the hydraulic valve block.

2.   Boeing and the safety agencies believe further rudder reversals will be prevented by a change in the hydraulic valve system that controls the rudder.

3.   A key question before them is whether the rudder design, driven by a single hydraulic valve, meets the standards for redundancy.

4.   He and others expressed frustration about the failure to find scars, cracks or other evidence of a jam on the hydraulic valve or other parts of the system.