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Fleet Reliability - Root Cause Analysis
The primary purpose of a root cause analysis is to understand what went wrong. You are looking to identify something that is broken – or not working the way it is supposed to. Your final conclusion may not always be a broken mechanical part. It could be an improper procedure, poor troubleshooting, a weak preventive maintenance program, a design issue, a life cycle issue or a human factors related issue. In all of these cases, you have identified something that is not working the way it is supposed to – and needs to be fixed.
An effective root cause analysis seeks to identify all potential causes. Quite often, poor reliability is the result of multiple causes. Therefore, your analysis should not end after one cause has been identified. You should continue to review all of your data until every potential source of trouble has been considered. If the end result of your analysis reveals several contributing causes, then you should address each and every one of them.
In general, there are several common types of fleet reliability issues. At a minimum, your root cause analytical processes should consider these issues:
1. Chronic Aircraft – This is when a specific aircraft continues to have the same problem
over and over again – regardless of the maintenance actions accomplished to fix the
problem. Sometimes more than one aircraft can have chronic problems at the same time.
2. Design Deficiency – These problems will be evident when the aircraft are new. A design
deficiency affects nearly all aircraft in the fleet. Make sure your problems are indeed
fleet-wide before labeling your problems as a design issue.
3. Marginal Design – On occasion, an aircraft system malfunctions when other parts of the
system begin to degrade – or the system is operated in extreme environmental conditions.
A good example of this is an air conditioning system that performs poorly in very hot and
humid conditions – but operates well in more moderate environmental conditions.
4. Modifications – On occasion, a modification can cause unintended consequences. If the
modification itself is the cause, you should notice similar problems on all modified aircraft.
Sometimes a modification is inadvertently done wrong. An example would be crossed wires,
a bent pin or an intermittent wire splice. This improperly performed modification will reveal
itself as a chronic aircraft.
5. Life Cycle Issues – Life cycle refers to an expected wear out period. If you begin to
notice an increase in component removals – where most of the components have similarly
high Time Since Installation (TSI) – the components may be reaching the end of their useful
life. Depending on the impact these failures have on your operation, you may want to check
the remaining life of the components on the rest of your fleet – and remove them before
they fail.
6. Chronic Components – This website contains a whole section dedicated to component
reliability issues. Rogue components are known to cause significant fleet reliability issues –
especially when multiple rogues exist in a component population. See the “Component
Reliability” tab for a detailed description of common component issues.
There are other types of issues that can cause fleet reliability issues. However, the ones mentioned above are the most common. Your root cause analysis must be able to identify these types of issues quickly and accurately. This will enable you to develop and implement effective corrective actions – to restore the inherent reliability of your aircraft systems.
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