Book excerpt: An unflinching look at the unique challenges posed by complex technologies we cannot afford to let fail—and why the remarkable achievements of civil aviation can help us understand those challenges. Nuclear reactors, deep-sea drilling platforms, deterrence infrastructures—these are all complex and formidable technologies with the potential to fail catastrophically. In Rational Accidents, John Downer outlines a new perspective on technological failure, arguing that undetectable errors can lurk in even the most rigorous and “rational” assessments of these systems due to the inherent limits of engineering tests and models. Downer finds that it should be impossible, from an epistemological viewpoint, to achieve the near-perfect reliability that we require of our most safety-critical technologies. There is, however, one such technology that demonstrably appears to achieve these “impossible” reliabilities: jetliners. Downer looks closely at civil aviation and how it has reckoned with the problem of failure. He finds that the way we conceive of jetliner reliability hides the real practices by which it is achieved. And he shows us why those practices are much less transferrable across technological domains than we are led to believe. Fully understanding why jetliners don't crash, he concludes, should lead us to doubt the safety of other “ultra-reliable” technologies. A unique and sobering exploration of technological reliability from an STS perspective, Rational Accidents is essential reading for understanding why our most safety-critical technologies are even more dangerous than we believe.