Hempy (and others)
I've been taking a long break abroad with Mrs. Engines, so not so much posting recently.
I don't think I can add much to John Farley's responses, which cover all the angles as far as I can see.
The only thing I would add is that people should understand that the F135 development programme was required to 'push the envelope' to a very high degree in terms of thrust/weight ratio as well as src, and many other demanding performance targets to support all three variants. It's a very large diameter engine, and I'd think I'd be safe in assuming that this might have contributed to the rubbing between the rotors and the casing - it could be that P&W's models for this effect didn't hold up under all loading conditions. But that's pure speculation. In any case, it's a much tougher issue to prevent than with smaller engines.
It should also be appreciated that the entire propulsion system is a separate programme between the DoD and P&W, with the results being supplied to LM as Government Furnished Equipment (GFE). As a result, this problem is firmly in the DoD's court with P&W to solve.
Given all the above, I'm quite surprised that the programme has not had more engine issues to date. Almost all combat jet aircraft programmes I have looked at have had significant if not serious engine problems at one time or another. The UK have had some especially bad ones, as have the US. This one is serious, no doubt about that, but as JF so wisely says, this event is 'pure engineering gold'. More so as no-one got hurt during it. It will definitely help the engineers at P&W deliver the best possible product to the front line as soon as possible.
Hope this helps, best regards as ever to all those exceedingly clever propulsion engineers who have to cover the 'hard yards' for real
Engines