Definitely sobering news and my condolences to the families and friends of the crew.
Firebombing is a hard on airframes and not completing your mission has graver implications than Mr Bloggs not getting to his destination.
The Herc has specific fuel requirements relating to Mzfw and the structural strength- eg if you flew till she ran dry the last fuel should be in the outboards. So flying in bs turbulence at low altitudes with 20k odd litres of retardant in the back and having a minumum of weight (fuel) in the main tanks means obviously that your wing spar is copping a flogging. As someone said these acft have high TISs as well- some as high as +90k hrs... and not sitting at flight levels much either... Unfortunately i have heard through the "grapevine" that this particular machine had a recent history of flap binding problems- why it was let to continue to its tragic conclusion will be left to the inquiry i guess.
HJ