• Published: 2 Nov 2011
  • Incident ID: 3395

Defective Clutch Results in Dropped Top Drive

Cause & Consequence

  • Other
Incident Consequence

Incident Location

Drilling unit

Incident Activity

Drilling, workover

Lessons Identified


 The operation was stopped during the process of breaking off the stand, rather than waiting until the Driller had the block at the floor for the start of the cycle; The rig operator did not notice that the clutch had not dumped its air when the clutch control was released to neutral;

 The clutch control had debris in the control mechanism, thus preventing the air’s release and signaling to the dump valves to dump the air to the clutch;

 The Driller noticed the brakes were not acting normal about two stands before the incident took place, but thought that the brakes had merely gotten water on them;

 The brake flange was leaking water and the driller thought the sluggishness of the brakes was due to water on the flanges.

Incident Recommendations


To address this incident, this company did the following:

 Instructed Drillers not to hand over control of the rig in the middle of breaking out a stand—set it back and bring the blocks to the floor in order to begin a new cycle in the procedure.

 Instructed Drillers to listen for changes; investigate smells; investigate the feel of controls or any changes in vibration.

o Things have a “normal” sound, appearance, smell and feel. The Driller should have investigated the cause when the brake felt sluggish for the two prior stands.

o A change in the sound of the brake or the sound of the air in the clutch dumping a few seconds late are indicators that something is wrong.

o If the brakes become wet the sound changes as they are applied.

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