I had first suspected a fuel/engine-related explosion as the cause of the wing separation, but this article indicates the wing may have failed first...  don't know much about internal inspections on these planes, but it seems either the cracks couldn't be detected during normal inspections, or some corners were cut along the line. Either way, tragedy aside, this is going to be a big problem for this tenacious little airline...

http://www.yorkdispatch.com/nationworld/ci_3330461

Oh sure, the media will go on and on about the age of the plane... typical.
  If there was cracking that was missed during inspections, there's no doubt that the marine environment and many water takeoffs and landings (often in pretty choppy water- there was actually a fatal crash of another Chalk's bird years ago, attributed to landing in rough conditions) was more of a factor than chronological age... we all know how long an aluminum aircraft can last if pampered and protected...

Quote:

I think it's pointless to make wild guesses & it seems they have enough of the aircraft to do a proper & thorough investigation. These sort of cracks take a long time to develop & if this is the cause they would have been there for a very long time. The wing spars of a floatplane take a lot more punishment than on a conventional aircraft as they're contintually subjected to stress transmitted through the wingtip floats all the time they're on the water. Landing & taking off from rough water puts even more strain on them. This could easily result in metal fatigue over a period of time.