At 9:00am after major maintenance and inspection of travelling block and replacement of drill line, Rig Tool pusher and driller were reeving the new drill line into the draw work drum. While scooping out the mast they were continuously lowering the travelling block keeping it at 4 meters height. After upper section of mast was fully scooped out the locking pins of mast were engaged where travelling block was at height of 6 mtr with 33 wraps left on draw work. The driller then started lowering the (5 ton) traveling block from a height of 6 mtr. to rig floor level. When the block reached height of 0.5 mtr from the rig floor, it continued to descend and finally leaned down and rested on the Rig floor. The fast line disconnected from the clamp and came down to the rig floor from the fast line sheave.