During the initial design phase of the aircraft a Reliability engineer will perform a Failure Mode Effects Criticality Analysis (FMECA) on each system. It is imperative that this is done prior to the finalization of any part of the design. The FMECA will define the effects on the systems of an aircraft and if and how the effect can migrate up to the aircraft level. He will also show the method by which the pilots are made aware of the failure, which drives the design of the monitoring and display systems. This in turn drives the development of the operating and trouble shooting provided in the operations handbook as well as the troubleshooting guides for the maintainers..
Now, let’s enter the real world. Because of monetary constraints Reliability, Maintainability, and Systems Safety analyses are performed after the design has been frozen. So the FMECA will reflect the design and not influence the design. In this situation the pilots and maintainers are left holding the mucky end of the stick when a problem occurs. If the engineers did not think of it, it is not incorporated in the design until there is an accident.
