Stan My thoughts exactly... im no expert on anything but as far as i have seen the tiger moth is constructed with a tube steel fuselage with wood wings and tail surfaces. The wings are constructed using SINGLE piece wood spars routed into an I beam shape attached at the root and interplane struts with bolted metal fittings (steel?) and wood ribs glued to the spars.
A catastrophic wing failure such as this suggests to me that the failure occurred in either the spar, root attachment or interplane strut attachment. The slats themselves would probably fail long before the wing would and flicking into a spin as Kharon described would have been a fairly regular occurrence back in the days when the tiger was the back bone of flight training.
Also im wary of statements such as
But, I found this interesting quote from an earlier report link, "The aircraft was stressed to withstand maximum loads of approximately 7.5g (acceleration due to earth gravity). Information from the manufacturer indicated that even with the reinforcing doubler delaminated and ineffective, the aircraft was designed to withstand manoeuvre loads of about 5g."
i dont have my original tiger moth pilots notes or DH service manuals handy but im fairly certain it makes no mention of G limits (none of the other DH manuals i have do - indeed the leopard moth one i have in front of me doesn't even list a VNE). stress analysis of individual components may indicate load factors as high as 5 or 7.5 but this may be a case of applying modern ideas of structural analysis to older aircraft designs.
Although both wood and steel do not fatigue in the same way aluminium structures do any structure where you have joints consisting of different materials with different stiffnesses will suffer from a kind of fatigue particularly if they are subjected high loads. Im fairly certain the tiger was not designed with anything other than gentle loops rolls and spins in mind...
anyway this is a terrible tragedy and my sincerest condolences to those affected