Risk experts (Mullane, 2006) have identified a pattern of human response that helps to explain many similar accident events; it is called the ‘normal­ization of deviation’. Looking back at the Toronto Airport case, suppose that the practice of using older tires beyond their service life had succeeded in the past. Since the apparent result showed better airline economics, the practice would be encouraging to management; it would become the normal practice. Certainly, this pattern emerged in the case of the Challenger booster rockets. Previous launches had succeeded even though the O-ring seals had leaked — the practice of launching with off-normal seals had become normal. The same behaviour pattern existed in the case of the Columbia external fuel tank insulation failure. Insulation had fallen off the tank during launch several times and had sometimes hit the orbiter, but the mission still succeeded. Observing insulation loss during launch had become normal. It will not be surprising if this same pattern emerges from the Deepwater Horizon investigation when that is completed. There are many other earlier examples that could be cited.