Software FTA

Including software in a system Fault Tree Analysis or quantitative hazard analysis is essential in software-heavy systems. Software does not only fail, it is often included as a mitigation element to hardware failures. A system analysis is incomplete without including the software elements and the interfaces between software and hardware.  SoHaR's software reliability engineers have experience in performing software FTAs and integrating the analysis into a system-wide Fault Tree.

A common obstacle to including software in a quantitative analysis is the lack of a failure rate estimates for these components. If the software is not part of a safety critical system/function it may be fielded with a known failure rate (based on the software testing program). In this case this failure rate may be used as an estimate for the fault tree analysis.  For more about the failure rates and reliability of software see Software Reliability. If a system is safety critical it is usually assumed that it will be fielded only after stringent testing which will show no remaining defects in the software code. Any remaining sources of failure (associated with the software) can be assumed to be the result of incomplete requirement definition, in particular requirements dealing with rare and anomalous conditions such as hardware failures, rare environmental and usage conditions and unforeseen operator actions. Often combinations of multiple rare events will lead to conditions that the software was not prepared for. An approximate rate for such events can be estimated from the code size, number of interfaces and the quality of the requirements document.  SoHaR engineers have experience at identifying the input and providing such an estimate.

To perform a complete software FTA our engineers will work with your program to obtain all the required data and information:

• System architecture

• system requirements document

• preliminary/functional hazard analysis

• hardware failure information

• human error information

For more information about our software reliability services please contact us at

becky@sohar.com
310-338-0990 ext. 101