ROV dropped to seabed

What happened?

During recovery of an ROV system, the ROV TMS (Tether Management System) experienced a problem latching to the LARS (Launch and Recovery System). The umbilical was damaged directly above the Docking Bullet on the TMS,  and was then sheared by the A-Frame docking head latch mechanism. The ROV then dropped into the sea and subsequently landed on the seafloor in a safe zone.

What went right

No-one was in the line of fire and the potential zone of impact during the event.

What went wrong

• An excessive amount of cold and dirty grease was in the latch mechanism which resulted in a slower than expected latching motion;
• The operator of the LARS system could not see the mechanical locked position indicator before releasing the umbilical tension, which resulted in a failed latch attempt. After repeated attempts to dock and lock, the umbilical separated with the result that the ROV fell into the sea and dropped to the seafloor.

What was the cause

• The latch mechanism was not cleaned and lubricated to OEM specifications;
• The LARS procedure specific to the installation was not followed;
• Supervision did not verify the correct maintenance plan nor the LARS procedure before work started.

Lessons and actions

• The latch design can damage an umbilical if it functions improperly and operates incorrectly;
• The company took the following actions
  • Restored latch functionality to normal by cleaning and lubricating, then verifying, the components function per OEM specifications;
  • Reiterated that crew should follow the LARS procedure for the specific ROV system onboard;
  • Ensured that supervisors verify that the correct maintenance plan and LARS procedure is available and is used for the specific ROV system onboard.

Members may wish to refer to:

• High potential near-miss: Dropped ROV/TMS leading to equipment damage
• Equipment damage – dropped ROV/tether management system (TMS)
• Loss of ROV: dropped object