Forbes: The Real Reason For Toyota's Troubles

[Omaha Steve]

http://www.forbes.com/2010/04/26/engineering-oring-tufte-technology-cio-network-toyota.html?boxes=techchannelsections

Kenneth G. Brill, 04.26.10, 06:20 PM EDT

Kenneth G. Brill is founder of the Uptime Institute.

The automaker's recent problems were likely masked by multiple, unrelated technical problems.

Sudden and unexplained acceleration problems with Toyota vehicles have dominated the news recently. I suspect that when the source of this problem is finally found, it will follow my thesis on reliability: at least five and as many as ten things must interact to produce the failure of a well-designed system. Any one thing by itself will cause a problem but not a catastrophic event. Think of a package of sliced Swiss cheese. The probability of being able to see through a stack of five slices is fairly low, provided the holes are reasonably small and the slices are randomly placed and some are rotated 90 degrees. Now increase the stack from five to ten slices and the odds of being able to see through the stack drop even further. But every time the holes line up, you can see clear through the stack.

How does aligning holes in slices of Swiss cheese apply to the Toyota ( TM - news - people ) sudden-acceleration problem? From the news reports I have read, it appears that the acceleration problem is random and occurs in some vehicles while not in others. As an engineer I believe that there is a root cause of these failures, but it is being masked by interacting issues. Just like the slices of Swiss cheese, when all the holes line up, the vehicle accelerates out of control. The problem for Toyota is identifying the separate slices of cheese and how they interact. Once these interactions are understood, the holes, or the orientation in only one slice of cheese, need to be changed to prevent failure. For redundancy perhaps change or reorientation of two slices is required.

The Challenger shuttle launch failure in 1986 that killed seven astronauts and embarrassed the U.S. in front of the watching world triggered a 34-month intense investigation during which manned flight was halted. Ofttimes when technical people intensively work on these types of problems, they get lost in details and fail to see the big picture. They also talk in terms that are confusing to managers and executives.

Edward Tufte in his book Visual Explanations and Steve Fairfax of MTechnology make a very compelling case that the official investigation focused too much on the O-ring itself and overlooked a very simple but decisive factor. It was logical to look at the O-ring design because erosion ultimately did allow hot gasses to escape, causing the rocket to blow up. But the case (or slices of Swiss cheese) for O-ring erosion did not correlate with the actual data (i.e., the holes did not line up). When ambient outside temperatures below 40 degrees

FULL story at link.