One theory
One theory is that water ingress of the honeycomb cowling wall followed by freezing/heating cycles may sufficiently weaken the cowling for it to implode during maximum negative pressure in front of the first stage turbine blades, such as you would expect during takeoff.
Another theory is FOD ingestion but the lack of apparent turbine blade damage seems to negate that.
Let's see what the ATSB has to say ...
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Philip
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