Functional Hazard Assessment
The Functional Hazard Assessment (FHA) is a safety assessment technique defined in SAE ARP4761. It is very different from Fault Hazard Analysis also known by the same abbreviation.
What about Functional Hazard Analysis (MIL-STD-882E)? Is this the same thing? Well, let's put that to one side for now.
An SAE ARP4761 Functional Hazard Assessment is a systematic, comprehensive examination of functions to identify and classify failure conditions of those functions according to their severity. What types of hazards does it not cover - that's right! the FHA does not focus on certain types of hazards. Let's put that to one side as well.
A Functional Hazard Assessment is performed at two levels - system-level and subsystem-level. The system-level Functional Hazard Assessment is a high-level, qualitative assessment of the basic functions of the system as defined at the beginning of system development. The system-level Functional Hazard Assessment identifies and classifies the failure conditions associated with the system-level functions. The classification of these failure conditions establishes the safety requirements that the system must meet. The subsystem-level Functional Hazard Assessment is also a qualitative assessment, which is iterative in nature and becomes more defined and fixed as the system evolves. It considers a failure or combination of system failures that affect a system function.
The output of the system-level and/or subsystem-level FHAs is the starting point for the generation and allocation of safety requirements.
If one is not methodical in their approach, FHA can be difficult to effectively apply such that you are not simply generating reams of meaningless tables, but instead are gaining a better understanding of the effect of failures and therefore a more complete list of hazardous failure modes. Identifying and defining functions at the right level of abstraction can be a non-trivial exercise. Care must be taken when extracting functions from requirements documentation to remove premature implementation detail.
Well, that certainly was descriptive, wasn't it? And you can look at SAE ARP4761 for a sample FHA. So what's the catch? The catch is that you still don't know how to prepare for and conduct the FHA. This is a recipe for mayhem and missing failure conditions.
Want to learn more? SAE ARP4761 and much, much more. Take our Aviation System Safety Course which dates back to 2007. Find out what the attraction is.
We are often contracted out, by end customers, to review FHAs and other 4761 documents. Perhaps our paths will cross.
Contact us if you would like to purchase an FHA Data Item Description (DID). You won't find a DID of this caliber elsewhere.