On Thursday, April 2, 2015 at 2:44:59 PM UTC-6, Dave Nadler wrote:
Yikes.
http://ad.easa.europa.eu/ad/2015-0052-E

Based on Mr Nadler's description, failure more or less inevitable.
Too small a radius will reduce the part's fatigue limit by somewhere between one third and one half roughly speaking. A 90 degree non-radius would result in a more or less infinite reduction in the fatigue limit (which is the stress on a part below which it should have an infinite fatigue life; in the real world all sorts of things reduce this limit, as we are seeing).
Rough machining can be even more insidious. Each piece of rough machining that you can see by eye is more or less the same as an already existing early fatigue crack. Its root radius at a microscopic level is effectively infinite with a corresponding reduction in the fatigue limit. Very bad news especially when it happens at a designed in place of inherently high stress.
All they had to do was to add some hard chromium plate on any wear surface that ran around the radius and failure would have been even earlier.
Pretty basic stuff. For it to have been repeated, as seems to have happened after a known problem, amounts to extreme carelessness.