Failure Mode & Effect Analysis (FMEA)
Failure Modes and Effects Analysis (FMEA) is a step-by-step approach for identifying all possible failures in a design, a manufacturing or assembly process, or a product or service. "Failure Modes" means the ways, or modes, in which something might fail. Failures are any errors or defects, especially ones that affect the user and can be potential or actual. "Effects Analysis" refers to studying the consequences of those failures. It is commonly applied to systems that cannot fail even when several critical components in the system have.
The FMEA discipline was originally developed in the United States military. Military Procedure MIL-P1629, Procedures for Performing a Failure Modes, Effects and Criticality Analysis, is dated November 9, 1949. It was used as a reliability valuation technique to determine the effect of system and equipment failures. Failures were classified according to their impact on mission success and personnel/equipment safety. It was later used in the aerospace industry to avoid errors in small sample sizes of costly rocket technology. The Apollo Space program is an example.
In the maritime sector, FMEA is conducted on a 5-yearly basis to determine the single-point-failure tolerance of the DP system of vessels. DP system works as an autopilot mechanism that the crew relies on to maintain the vessel's position whilst they can focus on other critical activities. These activities are usually done in crowded waters where losing position can lead to catastrophe. FMEA is integral to the reliability of the DP system and a critical component for charterer in evaluating the vessel's DP worthiness.
Worst-Case Failure Design Intent (WCFDI)
The worst-case failure design intent is the basis for the design and operational criteria set out for the vessel at the concept stage. It is the single failure mode that can be tolerated which has the maximum effect on DP capability were it to occur. It usually relates to the number of thrusters, generators and control equipment that can simultaneously fail and reduce positioning capability following the single failure.
Worst Case Failure (WCF)
The worst-case failure is the identified single failure mode in the DP system, resulting in the maximum detrimental effect on DP capability as confirmed by the FMEA study. It should, of course, not exceed the WCFDI unless it is proven that the vessel has an accepted post failure DP capability after the WCF identified in the FMEA has occurred.