To: BIT
Whether you want to continue this discussion or not, I will respond to your statements. If you wish to respond that is your prerogative.
An FMEA and an FMECA are basically the same thing. The C stands for criticality and it references the criticality requirement of Mil Std. 882 or, the FAA / JAR or, the CAA. There are four criticality levels. For the FAA there are 3 levels. Depending on the contractual requirement one or the other analyses will be used.
CAA 1 Minor JAR Same as CAA FAA Non essential Mil Std. 4 Minor
2 Major Essential 3 Marginal
3 Hazardous Critical 2 Critical
4 Catastrophic 1 Catastrophic
The above categories are tied to the frequency of occurrence related to number of hours flown by the fleet of a given type of aircraft.
It is true, the hazard analyses are worked on by many people and the various reports that are generated reflect the perceived safety of each of the aircraft’s systems based on the use of failure rates that are factored using Boolean algebra. However they are not pulled together to reflect the overall operational safety as to do so it could be shown that at the aircraft level the combined systems do not meet the safety requirements of the governing specification. If you know about this type of analysis each system is represented as a number of gates that must open to allow the failure to migrate up to the top level and the final gate is an and gate. If you take the top levels of each system and raise them one level to the aircraft then using this same Boolean logic it will show that the aircraft does not meet the spec. Once the analysis is complete it is not changed unless there is a major design modification and then only that part that reflects the change is modified. Normally by that time the design is in production.
The failure rates are defined in the reliability analyses, which also define the characteristics of the system to include redundancy. These number along with the redundancies are input into the FMEA / FMECA and then on to the Hazards Analyses.
The whole purpose of these various analyses is to drive the design. Once they are input into the design the company will lay off all R&M contractors and cut back on the department staff by moving them onto new programs. This in essence means that all work is stopped and if that is not cast in concrete I don’t know what is.
I'm sorry but this system does not respond well to tables.
[ 25 July 2001: Message edited by: Lu Zuckerman ]