Here at DMD Solutions we have been concerned by the history of the Boeing 737 Max crash in Ethiopia. As a company specialized in System Safety we were curious to know if, really, a mighty company as Boeing could have missed a SPOF. Here we are, it looks like the Preliminary Report of the Boeing 737 Max Accident based on the analysis of the flight recorders data, shows that the MCAS software failure could present a Single Point of Failure (SPOF).
For the people who are not familiar with this terrifying (for Safety Engineers) acronym: A SPOF is a flaw in the design of a system, in which one component malfunction causes the failure and non-operation of the whole system. If this failure is classified as catastrophic, it is not permitted by the certification agencies and the system must be re-designed by adding redundancy in the critical parts.
The issue becomes more complex when the problem is the identification the SPOFs in a very complex system as it can be the MCAS software of a commercial airplane. In this case, our tools as Safety Engineers to discover them is the development of specific analyses such as a Common Cause Analysis or a Fault Tree Analysis (FTA) which can identify these elements.
Specifically, in an exhaustive and detailed FTA, the computation of the Minimal Cut Sets can help understanding the vulnerability of the system. The Minimal Cut Sets show the unique combinations of component failures that can cause the System Failure, and if those come to be single events that can cause the failure, a SPOF will be identified.
At DMD Solutions headquarters, we are eager to get the Final Report of the Boeing 737 Max Accident.
In the examples below it is possible to visualise what a SPOF is. While in the Fault Tree, where the undesired state of a system is analysed using Boolean logic to combine a series of events, the Minimal Cut Sets is highlighted.