This Super Privateer 'Tanker 123' was being used by the U. S. Department of Agriculture Forest Service to drop fire retardant on the Big Elk fire near Lyons, CO.
The airplane was loaded with approximately 2,000 gallons of fire retardant, and 550 gallons of fuel and departed Broomfield-Jeffco Airport at 18:15.
The crew of a DC-4 ('Tanker 161') saw Tanker 123 in a base turn for the drop and in a "smooth 15 to 20 degree bank turn", when the left wing separated from the airplane inboard of the number 2 engine...
The aircraft pitched nose down in a huge fireball and plunged into the ground vertically starting an immediate large fire.
The investigations into the June 17, 2002 C-130A and July 18 P-4Y crashes looked closely 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.
The video
http://www.youtube.com/watch?v=tMCq22Vpa18 
