Report of the inquiry into the loss of Autosub2 under the Fimbulisen. Southampton, UK, National Oceanography Centre Southampton, 39pp.
(National Oceanography Centre Southampton Research and Consultancy Report, (12) ).
The Board of inquiry into the loss of Autosub2 under the Fimbulisen found that the loss was caused by a technical systems failure on the AUV. A comprehensive analysis was made of the technical reasons for the loss. However, because it was not possible to recover the AUV from under the ice shelf for direct examination, it was not possible to identify the actual cause of loss. Consequently an assessment was made of the likelihood of different failure modes causing the loss. The results of this analysis suggest that the loss was equally likely to have come about from an Abort Command (AC) as a Loss of Power (LP). A root cause analysis was performed which indicated that the source of the failure was most likely to have been a fault introduced during the manufacturing/assembly phase (52%), followed by Maintenance (25%). Design error was considered less likely (14%) while Operations (7%) and External factors (1%) were considered least likely.
This analysis indicates that the greatest benefits to reliability improvements are most likely to come from attention to faults originating in the manufacturing and assembly stage, followed by attention to faults arising from maintenance activities. Due to the large numbers of connections and leakage paths, it is necessary to pay particular attention to the reliability of electrical connectors and harnesses. A high level of quality assurance in manufacture and assembly is required to achieve an acceptable level of system reliability.
While it was accepted that the development team at NOC had adopted sound engineering practices in the development of the AUV and that reliability considerations had informed design decisions, the design team had no formally implemented reliability or technical risk assessment procedures to support design decision making. This was considered to be a major management weakness.
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