Originally Posted by
gums
My gut feeling is that the FBW design offered an opportunity to do "neat" things, and the sfwe folks went with a few suggestions. The emphasis upon auto-everything except putting on the brakes after touchdown and steering the jet to the ramp bothers me.
Well, based on what I was told by the people who were there, you're dead wrong. Don't let your experiences with a weapons outfit in the US make judgements for you on how a pan-European civil airliner project went down.
Also, CONF is a long-time hater of everything the 'bus stands for, so of course he's going to say that. To clarify for CONF, here's the supposedly "ambiguous" list of trim auto/manual status:
Normal : Auto
Alternate : Auto
Direct : Manual
RR_NDB claims that the Airbus system is an example of "Top [Down] Engineering", whereas in fact I was told it was a classic example of Top-Down specification with Bottom-Up implementation - meeting in the middle, which a lot of engineers claim is the most effective way to do things. The whole idea behind the "Laws" was to present a relatively easy set of mnemonics for pilots to understand the aircraft status - as such the A320 was the first airliner to attempt to address the problem of a non-normal situation increasing workload on the pilots in a 2-crew flight deck.
In the days of 3-crew operation, the Flight Engineer was expected to know the systems intimately, along with all the failure mode combinations and settings to maintain safe flight when those failures occurred. The only reason Alternate Law has sub-modes is because that knowledge of the systems is coded into the FCU logic - I'll say it again here - all a pilot really has to remember about Alternate Law is that there are no hard protections and that more care has to be taken to ensure flight envelope limits are not exceeded. If that's too complicated for the average pilot to understand, it's a wonder any pilot ever passed their IR*.
The implementation was "Bottom-Up" in the sense that Direct Law is the first layer of abstraction, providing straightforward control of the surfaces via digital means. Alternate was the next layer, roughly analogous to the old A300/A310 protections which activated only when the pilots let go of the controls. Normal was the third and final layer, which added the advanced FCU protections that made the Airbus FBW series seem like such an advance - when it was in fact only an iterative improvement over the previous generation.
Even the supposedly more "pilot-centred" B777 has more than just "manual" and "autopilot" modes, and again as I've said before, the force-feedback logic is itself far more complicated under the hood than anything in any of the A320's systems.
[* - Note to those for whom English is a second language - what I'm actually saying here is that I don't believe that the average pilot would find the flight control law system on the Airbus FBW series too complex to understand.]