Trencher angle inadvertently altered

What happened?

During offshore trenching operations, the ROV pilot unknowingly made contact with the control joystick, inadvertently raising the cutting wheel and thereby decreasing the cutting depth.  No equipment or permanent material damage occurred.

The pilot inadvertently operated the tool tilt function by making accidental contact with the joystick control.  The subsea trenching tool was lifted to 4 degrees, which raised the tool depth from 1.17 meters to 1.06 meters, resulting in the depressor depth being reduced.  This went unnoticed for approximately 7 minutes while the shift handover was taking place and equated to 27 meters of travel along the product.

What went wrong?

  • The pilot inadvertently made contact with the trencher control joystick;
  • The joystick and software design did not include controls to reduce the possibility of accidental joystick activation (e.g. joystick lock, dead-man switch);
  • The tooling alarm tolerance range was set too broad (-0.2° to +0.5°);
  • Trenching operations were not stopped to complete the shift handover;
  • The pilot/s did not notice the change to the trencher angle as they were distracted by both the shift handover and the reboot of a crashed control computer which was underway at the time.

What actions were taken?

Immediate preventative actions were put in place, which included change in the alarm tolerance with trenching operations ceased during shift handovers and the operating panels being set to maintenance mode, so the joysticks are deactivated.

  • Although this alert focused on a trencher the findings are transferrable to a wide range of equipment; therefore a review of equipment controls (such as joysticks) that could be inadvertently operated, or activated unknowingly, without an audible and/or visual alarm or joystick lock capability should be carried out;
  • Consider carefully your method of handovers during live operations and the implications of reduced focus on the activity during this time;
  • Ensure that personnel involved in operations have access to procedures, manuals and have demonstratable awareness training of associated equipment and processes;
  • Consider change of controls, processes, procedures and physical layout of control systems that would prevent a similar incident.