A rig had an incident involving the cranes while rigging up. The mast had been positioned and prepared to be hoisted and pinned to the sub-base. The lift was to be made by two cranes, one a 65-ton crane and the other a 40-ton crane. The 40-ton crane was being used to lift the crown end of the mast. Both cranes had been properly positioned to utilize their lifting capabilities and still be able to make a swing. The mast was hoisted and held stationary for a moment to ensure both cranes were able to make the required lifts. The mast was being moved into position when the right stabilizer leg began to buckle on the 40-ton crane. The crane began to tip over. The operator abandoned the vehicle without attempting to lower the load. The mast impacted the ground softly as the weight of the crane counteracted the fall. Damage to the mast was negligible. The 40-ton crane was removed and replaced by another unit. The pinning was then completed successfully. The company’s alert stated that apparently the piston to the outrigger was defective and caused the incident to occur.