The site of the leading fracture was at the "terminus" of the thread root on the fMS. This suggests a couple things. First, a machining issue, where stress is allowed to focus at the tooling insult. This could also lead to susceptibility to degradation via corrosion, and failure. The problem is that corrosion that happens so quickly seems unusual.
Since all failures happened on the ground, my first guess would have been FOD.
As with the RRTRENT spline AD, the possible link of coupling issues with powerful vibration and consequent failure of downstream internals is present with the GE.
The underlying issue may be a flirtation with minimum materials, both dimensionally, and inadvertently, in spec, and unproven economics.
The 2B is fit on the puffing Boeing, the 1B on the Boeing that has pneumatics independent of bleed air. The 2B is nine inches shorter, and has one less LPT stage, case in point?
Edit to correct, the 2B is the shorter engine...
Also to say that what goes through the engine is not air, but MASS.
4000 pounds of it, each second. That they stay together for the most part is a triumph. Hat's off, to all the engine builders....
Last edited by Lyman; 9th Oct 2012 at 14:14.