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This month's newsletter discusses a current event - in fact the single largest consumer product recall in US history-- as an example of what the rigorous practice of Critical Parameter Development and Management could have prevented.
I am referring to the recall of the airbag subsystem developed and produced by Takata. The first complaints of this defect were filed with the US National Highway Traffic Safety Administration (NHTSA) in August 2013. The recall now includes approximately 34 million vehicles in the US, manufactured by 10 different automakers, fitted with potentially defective airbags. The failure effect is described as "explosion resulting in the projection of shrapnel into the face and body of both the driver and front passenger". The defect has been linked to 6 deaths and over 100 injuries. In addition to the physical harm the defective bags can inflict, the recall is expected to cost billions (with a "b") of dollars, overwhelm the automobile supply chain, and take years to complete.
As recently as June 2, 2015, questions remain about the root cause and the solution to the problem. On that day, the US Congress held a hearing, An Update on the Takata Airbag Ruptures and Recalls, where Kevin Kennedy, Executive VP at Takata, testified
Based on this research and our ongoing testing and analysis of returned inflators, Takata's best current judgment (emphasis mine) is that the potential for rupture is related to long-term exposure, over a period of several years, to persistent conditions of high heat and high absolute humidity. In certain circumstances, these conditions can result in an alteration in the propellant wafers in the inflators that could potentially lead to over-aggressive combustion.
At the same hearing, Dr. Mark Rosekind, Administrator at the NHTSA, stated that the root cause is not known at this time. He testified
So while NHTSA's analysis of the data shows that prolonged exposure to hot, humid climates is associated with greater risk, the full story is not yet known and a definitive root cause has not been identified. In my recent experience as a Member of the National Transportation Safety Board, I know there may not be a single root cause, and we may in fact never know the root cause.
From Kennedy's (Takata) testimony, it would seem that after this failure was detected, Takata looked into the failure mode and determined after-the-fact (after product launch) that the subsystem was sensitive to the Noise factors identified as high heat, high humidity and time. Based on Rosekind's (NHTSA) testimony, it would appear that there is no data to prove that even the fixed, new units being installed in recalled cars are "totally safe".
In CPD&M terms, the Design Guide, a summary engineering document, would provide such proof, preferably pro-actively (before product launch). A Design Guide would include following detailed data summaries:
- Design FMEA linked to one or more of the following documents: Functional Flow Diagram for the subsystem, Parameter Diagram(s), Noise Diagram(s), Fishbone Diagram(s), Cause and Effect Matrices, Fault Tree Analysis, and a Reliability Block Diagram. This provides systems-oriented documentation of what can go wrong in the functions that underwrite the proper sequence of functions that define the airbag subsystem's performance.
- Analytical and Prototype modeling data for the new, fixed subsystem that link math models and simulations to prototype-based physical performance data as they were evaluated for base-line (non-stressed) performance and stressed performance. They would have the evidence in the form of both analytical models and prototype models that prove the design was robust to not only humid conditions, but all noises that also affect the functional performance of the design. The airbag's "explosion function" must be measurable, stable, adjustable, parametrically understood based upon a Y=f(X) model, hyper-sensitivities identified and eliminated/mitigated, robust to all real noise factors and capable of meeting functional design requirements under both nominal and stressful noise conditions.
These are summaries of The Big 7 Critical Parameter identification results based upon the execution of a series of methods and best practices specifically defined and required to know exactly how and why such a subsystem works under the stressful conditions that Takata only became aware of AFTER they installed this safety-critical subsystem in vehicles sold to customers!
It is obvious there were critical parameters embedded in the airbag subsystem design. Takata sold their design to the car companies in ignorance of this. In turn, the system integrators, the car companies, have lax standards of acceptance that allowed such anemic designs to make it into their products. Takata, as many companies who develop complex subsystems, under-developed their designs. They failed to take the time to learn what is necessary to underwrite the functional integrity of their products and how they integrate within the larger systems under stressful (noise) conditions. The car companies also have an accountability gap in their relationship with their suppliers. They are not checking for critical parameter information across the functional requirements and candidate parametric relationships that define how their system of sub-level designs really works in the real use environment.
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