EE DISMOUNTED A D-11 DOZER INCORRECTLY, RESULTING IN HIS LEFT FOOT SLIPPING & HIS BODY FALLING FORWARD. HE WAS ABLE TO HANG ON TO THE GRAB RAIL BY THE ENGINE COMPARTMENT, BUT HIS LEFT FOOT BEC AME CAUGHT NEAR THE STEP, RESULTING IN A FRACTURE OF THE TIBIA & FIBULA ABOVE THE LEFT ANKLE.