Comments from the report:
It is mentioned in the report that task appropriate mode (TAM) and activity specific operating guidelines (ASOG) were in use, with the limitation identified for 2 DGNSS subject to common mode failure.
Considerations of the IMCA Marine DP Committee from the above event:
- Use of only 2 DGNSS was contrary to the MSc.1 / Circ. 1580 requirements. This meant the vessel was not set up in accordance with DP class 2 requirements of 3 position reference systems based on at least two different principles;
- Vessel sensors selection did not appear to comply with DP class 2 requirements, though this non-compliance was not a factor in the incident;
- Task appropriate mode was in place, indicating that a loss of position was acceptable. However, the incident indicates that an adequate risk assessment was not done and TAM and ASOG were not thoroughly reviewed prior to their approvals;
- When the vessel lost its automatic DP control due to the loss of all its PRSs, the position could have been maintained for a period of time using the DP mathematical model;
- The report states that interference from a faulty laser-based system on the PSV caused the loss of signals to both the DGNSSs. However, this could have been caused by interference of the differential correction signal receivers caused by shielding or reflection;
- Information on radio interference is provided in IMCA M 252 Guidance on Position Reference Systems and Sensors for DP Operations, Section 4.6 Operational Consideration Summary.
The following case studies and observations have been compiled from information received by IMCA. All vessel, client, and operational data has been removed from the narrative to ensure anonymity.
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