@ap08:
Graceful degradation based on maintaining familiarity. If you throw a pilot into a scenario where he or she will have to repeatedly perform an action that is not part of their day-to-day experience (such as manually trimming a FBW Airbus), then it adds a risk factor because they may not get it right. As such, Alternate Law exists when a partial systems failure means that Normal Law can no longer be sustained, but not all the benefits need be lost.
For a (very) rough analogy, when driving your car and the ABS system fails, you don't want it to take out the power steering and cruise control as well if the latter two systems are not showing any indications of failure.
Direct Law should only be reached in the air when the failures are significant enough that none of the FBW assistance can be relied on.
It's worth bearing in mind that despite all the in-depth discussion going on here, most FBW Airbus line pilots will never experience Alternate (or for that matter Direct Law in the air) outside of the simulator.
Originally Posted by
BOAC
I think we need to have a serious thought here about this 'progress' to software control. How many AB pilots would understand/anticipate EXACTLY what a movement or relaxation of the SS input would do in this situation?
It doesn't matter what aircraft you fly - it's expected that a pilot should understand that pulling back to maintain 15 degrees pitch up when at cruise level is a very bad idea!
Is it reasonable to expect a stressed human to work this out, especially one that may well have been inculcated with the 'AB will look after you' mantra?
That's an oversimplified line propagated by the press - I'd be very surprised if conversion training didn't include the caveat "as long as everything is working - if not you need to take extra care".
Surely the cry for a drastic overhaul in both philosophy and content of FBW training needs to become very strident?
I think that restricting an industry-wide review to FBW would be too narrow a focus. As PJ2 pointed out in Tech Log, the real problem is that from senior management on down, the peculiarities of the aviation industry is not well-understood anymore. In short, an MBA is not enough to run an airline safely.
Now, Alt2B - let me see C* - is that 1g or flight path, or is it perhaps constant pitch attitude......?
Doesn't matter - the only mantra you need to remember is that outside of Normal Law, extra care must be taken.
Do I have alpha protection in this mode or not?
Outside of Normal Law, no. Also not particularly difficult to remember.