Originally Posted by
misd-agin
How many rudder control failures have you heard about, from either system, that are related to the design of the rudder limiter? I can't recall any, which to me indicates that there's no empirical safety benefit from having fewer parts.
I don't know why Airbus changed the design. We have cost(proven), weight(proven), and better failure mode(hypothetical?). I'd vote for lower cost, weight, and ease of manufacture as the reasons behind the change.
Accepting that as your opinion, I'm coming at this from an engineering rather than an aviation perspective. Empirically speaking, the fewer moving parts you have within a system, the less parts you have that can fail through manufacturing faults and through simple wear and tear. It's a bit cold and clinical, but it is an engineering maxim nonetheless.
The fact remains that a variable stop system was used by Douglas as well as Airbus in aircraft that have been considered safe for decades, so any talk of deficiency in design is disingenuous to say the least.
The system on the A300 is sensitive, and as such not ideal - but then the variable-ratio lever system requires more frequent safety checks and is a less elegant design and therefore not ideal either. It's swings and roundabouts as to which is chosen and it's unfair to say that one system is superior to the other in all aspects.
As for the 737 rudder issue, Boeing's contractor Parker Hannifin developed a single-valve design to keep weight and costs down. It was an elegant design, however the engineering cost was a loss of redundancy compared to dual-valve designs. As such it was a problem specific to that model and that manufacturer.
I know that no matter how hard we try, we will always have a bit of national pride in our manufacturers and it's hard to avoid that flaring when we feel that they are slighted. In this case there is nothing inherently wrong with the A306/310 system as long as conversion training takes into account that the pedals are more sensitive than the pilot may be used to on other types.