Originally Posted by
Geoffersincornwall
As a mere pilot these technical explanations appear to reveal a situation in which the manufacturers of these gearboxes know from the outset that they are full of imperfections due to the very concepts behind their design. They then rely on being able to detect the inevitable failure courtesy of the infamous chip detector system. When this detection mechanism is found to have holes in it surely that puts the whole design philosophy behind this type of gearbox into question. How can the certification authorities support the notion that all is well in the helicopter transmission business? Is this behind the UKCAA and NCAA approach? How come the EASA experts don't get it? What kind of world are we living in?
Geoffers-
As Concentric pointed out, the analysis of this particular bearing case is a very complex non-linear problem. Even with the best computational analysis tools currently available, there are lots of assumptions and simplifications that must be used to make the analysis practical. Normally the assumptions and factors-of-safety used tend to give a very conservative result. But sometimes a "perfect storm" of problems occurs that the analysts did not consider, and the result can be what we witnessed in this situation.
Don't blame the gearbox designers. They seemed to have done a professional job designing this gearbox given the engineering tools available at the time, and meeting existing certification requirements.