via spinex:
I'm not an engineer (perhaps just as well), but what I can see of the corrosion on the bore of the dowel hole wouldn't really run up any red flags if I'd seen it prior to the incident.
Reminds me of some corrosion i've seen on sprockets on farm machinery. A loose rusty bolt to thin for the hole it is in will give that 'smeared mud' effect seen in the lower left quarter of the ATSB photo. The next stage is the bolt rusts up enough to lock into place embedding the rust flakes into the sprocket hole.
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