Originally Posted by Rainboe
At some stage, you have to accept you can't back up all systems indefinitely, and still be able to carry a payload on an aeroplane. The design of the 747 has been refined over the years to make redundancy superb. Four hydraulic systems
The problem with hydraulics seems demonstrated by 3 cases of airliners suffering total hydraulic failure despite redundancies.
A300 had a rocket in one wingtip. The aileron was served by three redundant hydraulic systems... so they all failed, and the aileron at the other wingtip as well as the aerodynamic controls of tail, though mechanically intact, became useless. DC-10 had engine shrapnel in tailfin... again, it was served by all three redundant hydraulic systems, so they all duly failed and ailerons, flaps et cetera became useless. B747 has rear bulkhead failure... again, it broke all 4 hydraulic systems, so that e. g. ailerons at the end of, mechanically intact, wings became useless.
How do airplanes deal with this kind of multiple common-cause failures?