From what little the article has here, it seems that all of the valves are somehow tied in together at least one point, making a possible failure that would also take out the back up.
hgg, ive been following this story on my aircraft websites. in all modern aircraft, there are three valves all run by different computers, this eliminates the chance of bad data causing a catastrophic decompression. airbus has decided to change this protocol. in europe, this story came out as a typical american trying to make trouble. actually, that is easy to believe imo, as americans are way to baby like generally. however, this issue needs some serious investigation because this particular aircraft really will not be able to recover at all from such an incidence if it occurs, its simply to big and if it happens, people will be bouncing around like ping pong balls.
The way I read it, other planes have three systems, this one has four! But the guy is claiming that all four could fail simultaneously via some unknown software 'glitch'. We discuss this all the time in the nuclear industry. Our safety systems are typically four independent systems, of which 2 signals are required to shutdown the reactor. This leaves the ability to take 1 of 4 out for maintenance and 1 to 'fail' at the time of the event but still have 2 that would trip the plant. The concern is that they are all designed using the same components so we have to be concerned about common mode failures. Software is particularly sticky issue in this regard.