Prior to raising the mast, the traveling block was secured with rig floor shoe by means of a chain sling. Later, the mast was raised 1 meter off the stand and rig team waited for few minutes to confirm whether mast raising cylinder was holding. After being satisfied the cylinder was holding they decided to continue raising it. The mast was further raised up to four meters, the chain sling to be in tension resulting in the sling parting. Due to drill line pull, the block slid from rig floor and landed on the ground from a height of 5.10 meters. No injury happened NO GO was established.