As the aircraft slowed after a normal landing the right main landing gear and then the left main landing gear collapsed. The aircraft skidded to a halt on the fuselage underside. Examination of the broken section from the right landing gear strut showed that overload failure had occurred around a welded joint, inboard of the suspension bungee attach point. The investigation has shown that the aircraft manufacturer had previously identified a problem with the strength of the tubing being used in this section of landing gear. The manufacturer advised that an interim modification had already been incorporated on the aircraft production line, which increased the wall thickness of the tubing. In the longer term, it was proposed to modify the strut design to increase its strength.