SDR 510018592 Swearingen SA227DC Main landing gear yoke failed. LH main landing gear lower yoke fitting sheared causing LH landing gear wheels to turn sideways and skid along runway, causing aircraft to veer to the left and leave the runway and enter the sand. The landing gear then dug into the sand allowing the LH propeller to contact the soft ground. P/No: 2751505001. TSN: 20,160 hours/21,678 cycles TSO: 20,160 hours/21,678 cycles