About N130HP:

Hercules N130HP was hired to fight a 10,000-acre wildland blaze near Walker, CA. After dumping a red cloud of fire retardant, both wings separated in an upward motion. The right wing immediately separated from the fuselage at low altitude. The plane then lost control and rolled left. During this manoeuvre the left wing fell from the aircraft as well and the aircraft nose-dived into the ground. The whole event just took about 4 seconds and was captured on video a passer-by. In April 1998 two one-inch cracks were found on the bottom of a wing (the service difficulty report does not state which wing), at Outer Wing Station 33, which is 33 inch (83cm) from the wing joint. These cracks were repaired.
The investigations into the June 17, 2002 C-130A and July 18 PB-4Y crashes are closely looking at the fatigue cracks as well as other safety issues, such as inspection and maintenance procedures and operational factors. Preliminary results for both have indicated that widespread fatigue was not evident over the entire wing but that in some locations current crack detection techniques may have been unreliable.

PROBABLE CAUSE:

"The inflight failure of the right wing due to fatigue cracking in the center wing lower skin and underlying structural members. A factor contributing to the accident was inadequate maintenance procedures to detect fatigue cracking."