One more observation:
The NTSB, and especially the FAA, will rarely identify a serious problem until there is a solution available. They really didn't want to ground every 737 in the world indefinitely, as they did the DC-10 in 1979.
By the time the 737 yaw damper problem was conceded, Boeing had a retrofit fix, and a longer term fix for new 737s in the form of a new fail active rudder they needed for CAT IIIb, anyhow.
Planes with wing mounted engines may be a lttle more efficient than those with tail mounted engines, btw, but they require a much larger and more powerful rudder to fly on one engine. That magnifies the seriousness of a wayward rudder.
GB