Alert 14 – 24 Three Instances of Uncontrolled Descent of the Traveling Block Assembly
During troubleshooting of a Drawworks brake alarm there was an uncontrolled descent of the travelling block assembly to the rig floor resulting in equipment damage:
• The maintenance team was troubleshooting the Drawworks system for a brake status alarm that was preventing the top drive from breaking the upper connection. The initial understanding within the maintenance team was that the Drawworks brakes were set.
• Throughout the troubleshooting the maintenance team did not seek a clear understanding as to the condition of the brakes. This was further compounded by a Public Address announcement, which occurred during a critical phone call that resulted in the ongoing still believing that the brakes were set. As a direct consequence of those events, both drives were reset under the faulty assumption that the parking brakes were set.
• With no drives holding the load, and none of the brake calipers set, the travelling assembly descended to the floor.