Coordination fault occurs when all of the system components work properly, according to the rules, but still, regular operation ends up in undesired results.
A main source for coordination fault is wrong information of part of the components about the situation, namely, the components assume different operational states.
This problem is realized when the operation of a specific component does not match that of the other components.
During the operation, the operational scenario is implicit, and different components assume different active operational scenarios. The problem raises when a certain component is in an exceptional state, while the operation of the other components continues normally, because they do not have the system level information about the active scenario. In such cases, the system might not respond properly to the situation change, resulting in coordination fault.
Coordination faults are typical of systems that do not synchronize continuously, because the system constraints are not specified in the behavior documents.
In the TMI accident, the backup cooling system was not coordinated with the control room. The backup cooling system was not constrained to operated differently in normal operation. In this accident, it did not follow the transition from maintenance operation to power production.
A special case of coordination fault is when the cooperation fault, when at least one of the components involved is a human operator.
Coordination faults may be avoided by a special Scenario analyzer.
Intra-system inconsistency
This term refers to exceptional machine state, irrelevant to a particular stage in a particular operational procedure. The inconsistency is between the machine's units, as was the case with the Therac 25 accidents (Casey, 1998),
Inter-system inconsistency
This term refers to exceptional context, not mentioned in the system requirement specification document. The i nconsistency is between two sub systems, as was the case with the friendly-fire accident in Afghanistan, 2001 (Casey, 2006).
Updated on 16 May 2016.