FMEA and FMECA were first proposed by MIL-STD- 1629. But today's FMEA is not the FMEA at that time, and today's FMECA is similar to that at that time. In other words, today's FMEA is also the FMECA at that time. The development of the times has given FMEA/FMECA more contents. At first, there was no such thing as RPN in FMEA.
Automobile industry is the earliest and most successful industry to use FMEA (except military industry and aerospace). Of course, the automobile industry also expanded FMEA. At that time, it actually became a qualitative FMECA. The success of FMEA in automobile industry makes other industries learn from it. Of course, at least at that time, the main consideration in using FMEA in the automobile industry was failure, not safety. Safety and availability are more important than reliability in rail transit industry. Of course, safety and availability are inseparable from reliability, so FMECA is more suitable for rail transit.
For industries related to IEC6 1508, such as rail transit, if you know its failure mechanism and every failure mode, you must do quantitative FMECA. If we don't understand, its standard requirements will be more stringent, whether it is related to architecture or monitoring and diagnosis. You can only do qualitative FMECA or FMEA.
FMEA and FMECA are the same standard in the early American military watches and national military standards, but the difference is that there is a C(criticality). After adding a C, there will be more hazard comparisons, and it will be easier to favor safety analysis in use, because the most important things in risk/safety analysis are severity and probability. Nowadays, FMEA has critical /RPN, and usually only those with quantitative probability are called FMECA.
According to the quantitative analysis required by IEC6 1508, FMECA is quantitative, involving many industries, such as nuclear power, aircraft, rail transit, petrochemical and so on. In other industries, such as IEC6060 1 medical treatment, only semi-quantitative analysis is needed. Interestingly, ISO26262 was recently published in the automobile industry, and quantitative analysis will be essential. In the near future, FMECA and QRA, an example of fault tree, can be used in the automobile industry. Another interesting thing (which is also somewhat confusing) is that in the medical industry, FMECA and FMEA usually require FMECA to do safety analysis (qualitative or semi-quantitative), while FMEA does failure analysis, usually using the template of automobile industry.