PJ2 wrote :
That aside, the point being made here is, the posited scenario is well within the realm of experience, (which is the reason I provided the example of the B727 'bump' upon disconnection), and not something that is an outlying matter or even a QF72-type issue. I'm not saying it's not possible - QF72 showed us that it is possible for FCPCs and FCSCs to misbehave, but that is not what is being claimed here.
TheShadow wrote :
...b. The prescribed failure hierarchy can be short-circuited sometimes. i.e. if it's anticipated that A will fail then B then C etc, any non-alphabetical scrambling of that design failure's graceful degradation sequence can become a true "spanner in the works". (I'm trying to think of an example here. Maybe somebody else will). There are a few EFIS systems around that have test switches labelled "maintenance only" (but accessible to flight crews) that can do weird things if cycled inflight.
Gentlemen,
I find these considerations highly interesting, especially given that there are two unexplained ACARS failure messages which did not seem to draw too much attention and which were dismissed rather lamely in the BEA report :
F/CTL PRIM 1 FAULT
F/CTL SEC 1 FAULT
The BEA states that these are either failures or commanded shutdowns.
If they were commanded (turned off by pilot action), one has to remember these switches are guarded, with a very obvious and specific grid-like guard.
You cannot switch them off by accident. But then, why in dark cold Hell would they have felt the need to switch both off ?
If they were failures, then why in the watery depths of Hell did both these computers fail ? They never did in the ACA incidents for example...
Thoughts ?