Originally Posted by
pravg
Pax2908's drawing shows exactly what was argued earlier. The LP compressor hub flange is fixed to the rear of the fan disc and is in fact only supported by the fan disc. When the fan separates from its shaft one would expect the LP compressor hub (together with its 5 stages of compressor blades) to be thorn out of the engine but instead the compressor hub mounting flange separated quite nicely, despite the many fastening bolts.
Just guessing here: The fan hub to shaft coupling is designed to withstand quite a bit of thrust (produced by the fan). But the fan hub to LP compressor barrel coupling not nearly so much. It's more for the torque of spinning the compressor. So an initial failure of the shaft to fan (where a jagged piece remains) would allow the fan to pull forward. The 24 (?) bolts holding the compressor stage failed under tension (photo in #194). That may be by design. To let the fan go forwardvwithout trying to pull the compressor rotor through the stator.