Originally Posted by
TTex600
The aircraft responds to the SS one way in normal law, and another in abnormal, and another in direct. Imagine, if you will, the steering wheel on your automobile randomly varying tire steering angle for a given steering wheel angle. Fun, huh?
[Car analogies - the staple diet of internet discussion boards, how did we manage so long without one ?]
Not so much random as predicatable change in feel. Not disimilar to power-steering failure... which happens. Most of us will never see it and never (these days) drive without power steering or remember what it was like.
However, in this case there was no change in control law in pitch axis - which was where it all went wrong - but a change in roll law may have pre-occupied the pilot and lead to failure to manage pitch. More like failing to steer the car right while worrying about accelerator or brake failure. Those do happen, and probably more often than steering fail. Many modern cars can go into a "limp home" mode for all sorts of failures (MAF sensor, DPF...) which is exactly the same principle as the degraded control laws. Fun ? Probably not, but not considered dangerous enough that drivers are given any training (or sometimes any information) in advance of it.
In the aircraft case, at least there is the sim to train and prepare for it. Except someone apparently decided it wasn't necessary to train the AF crew...
While we're on cars, it maybe worth comparing this case with the Prius accelerator issue. Initially blamed on the design/manufacture (type) and the computer control (fbw) going wrong. Turns out that in the end it's down to an age-old human-factors issue of not figuring out that something on the floor is stuck under the pedal. Yes, an element of bad design - floor-mat - but mostly HF issue that's happened before on other types. Just that the new computer control (and maybe the foreign mfr.) is a convenient initial scapegoat - one that some will still believe in even after all the investigation and reports are done and point a different way.
Also contributing is automation dependency - changes to reduce driver workload. Where a whole nation of drivers can't co-ordinate more than one foot, or take a hand off the wheel to change gear (because it's got a phone in it) - resulting in the removal of the mechanically connected clutch & pedal. Which, on those rare occaisions where your car decides to accelerate away uncommanded, is actually a really really important safety backup. [feel free to draw different conclusions on the a/c equivalent for that one].