To my way of thinking the AD/PZL/5 should have required the wings were removed for the inspection. It is hard to imagine that crack was not there 120hrs prior when the NDT was carried out, possible but....and there is nothing quite like physically eye balling the components particularly given their history and the overload allowance.
CASA and the manufacturer get around the over weight operation by simply fixing a sticker to the instrument panel stating overweight operation can reduce fatigue life and lead to structural failure.
I often wondered how seriously pilots took this warning and whether many made a conscious effort to modify the way they flew the aircraft.
Aside from the inherent increase in low level turbulence associated with fire bombing consider the lot of the Dromader airframe. It is a budget airframe with a low G envelope it also has a low speed envelope and low Vfe speed. Now combine that with a more aerodynamic engine install, greater power and potential for higher speed and a significant uplift approval lighter control forces and the fact that many likely use first stage flap running into and during the dump while flying very near or at Vfe limit speed, it all sounds like a recipe for a problem. My memory of the Vn envelope with first stage flap was something like +2.5/-0.5 G, not much
If the AAAA hasn't already I see a good case for a very sobering education program for the operators/pilots and engineers of these aircraft.