Originally Posted by
pilotmike
In any case, my main point is that there is no inherent mechanical force or tendency for the liberated blade causing "this radial trajectory [to] sustain after root failure" as you seem to suggest.
pm
Seems reasonable, trajectory after separation would certainly be chaotic.
But this does also assume instantaneous separation under tension (typical fatigue failure).
However the blade in operation is subject to considerable bending and twisting moment, cyclic with every engine power change or every time that the load on the blade changes. This could (is likely) to see crack propagation originating along the trailing edge surface, the surface under tension when the blade is bent forward.
It is conceivable that the final failure is not instantaneous, no matter how quickly it occurs, but occurs over the course of some part of rotation or full rotations of the fan.
Possible that final separation might occur progressively with the leading edge surface failing under combined bending / tensile load, at which time the tip of the blade could well be "hinged forward" to some extent.
Such a failure would be evidenced by plastic deformation along the leading edge fracture zone.
In routine inspection, is the focus on the trailing edge root area?