On June 9 2014, technicians on board the semi-submersible drilling rig Deepwater Nautilus were troubleshooting an alarm that was preventing the top drive from breaking its connection from the top of the drillstring.
The rig was pulling out of the hole and the traveling block was at the top position in the draw works.
A miscommunication between the technicians and the drill floor resulted in the assumption the drawworks brakes were set. This assumption proved to be incorrect and after resetting the draw works drive, the block began to fall on top of the stand of pipe which was set in the slips beneath.
The 6 5/8″ drillpipe collapsed under the load and the cables that supported the ~200k pound block and top drive spooled out.
According to a preliminary investigation report obtained by gCaptain, “At some point before or near the final resting point of the traveling block / top drive descent, the brakes were applied and the draw works drum was brought to a halt. Post event testing of the draw works brakes proved their capacity to be functional.”