on May 4, 2007
Air travel has become remarkably safe as a result of advances in equipment systems, operating procedures and training. Each year, flight crews deal skilfully with sub-optimal systems and unexpected situations during the course of around 17 million flights world-wide. Yet airlines operate in a highly competitive market with pressures to deliver unprecedented levels of efficiency, so it is now more important than ever to understand what makes the air transport system vulnerable to failure. Since most aviation accidents have been attributed to deficiencies in the performance of flight crews, it is particularly important to understand what makes pilots vulnerable to error.
In this outstanding and original book, the authors argue that human skill and vulnerability to error are closely linked: errors occur because flight crews are expected to perform tasks at which perfect reliability is not possible - either for humans or machines. The authors show that the presence and interaction of factors contributing to error is probabilistic rather than deterministic. Accidents are rarely caused by a single factor, but rather by the complex interaction of many factors that combine in ways driven largely by chance. The authors argue that small, random variations in the presence and timing of those factors can drastically increase the probability of pilots making errors leading to an accident.
Consequently, it is crucial to understand the nature of vulnerability to error in order to reduce that vulnerability. While it is not always possible to determine exactly why accident crews did what they did, the authors demonstrate that it is possible to understand the types of error to which pilots are vulnerable - and to understand the interplay of various factors contributing to that vulnerability. The central questions posed in this book are: why do highly skilled professional pilots make errors, with consequences that are sometimes fatal to themselves and to their passengers? And how should we understand the role of these errors in accidents in seeking to prevent future accidents? The authors apply scientific knowledge of the nature of skilled performance of humans performing complex tasks to address these questions.
The book reviews the 19 major accidents in US airline operations during the period 1991-2000 in which crew errors played a central role, as defined by the US National Transportation Safety Board (NTSB), based on the NTSB reports and associated documents. While the NTSB must determine the probable cause of each specific accident, the authors take a different approach: would other pilots be vulnerable to making the kinds of errors made by the accident crew and, if so, why? This original approach reveals factors that make all pilots vulnerable to specific types of error in certain situations. In adopting this approach, the authors challenge the assumption that, if expert pilots make errors, this is evidence of their lack of skill, vigilance or conscientiousness. Instead, the authors emphasise the interactions of subtle variations in task demands, incomplete information available to pilots, and the inherent nature of skilled performance. The authors go beyond accident investigation, therefore, to explore the common themes and `deep structure' underlying the accidents.
In addition to the stand-alone accident chapters, the authors provide a statistical summary chapter that extends an earlier study by the NTSB and that reviews accident data for a longer period (1978-2001). In the final chapter, the authors identify the main themes and implications of their study, suggesting specific ways to improve aviation safety. Many issues are raised, including the significance of crew familiarity, crew fatigue, first officer experience levels, unstabilized approaches, plan continuation bias, misleading or absent cues, and monitoring/challenging errors. The authors reframe these airline accidents as `system accidents' resulting from the lack of adequate information provided to crews, the inherent difficulties of assessing ambiguous situations, and the less than extremely conservative guidance given to pilots by the air transport industry.
Overall, this is an excellent and innovative text which reflects the authors' original approach to airline safety. The book is outstanding in its identification of common themes that run deeper than in previous analyses of aviation safety, and the final chapter contains clear, pragmatic guidance to the air transport industry and to researchers. In the final sections of the book, the authors sum up the central challenge faced by the industry in reducing vulnerability to error: pilots should be given more information, better interfaces and clearer decision-making guidance - backed up by prioritising adherence to that guidance over commercial pressures such as on-time performance.
The book will be informative for diverse readers in the air transport industry, including operational staff, researchers, safety analysts, accident investigators, designers of systems and procedures, training providers and students. Given the nature and scope of their study, the authors have focused on the US context, yet their approach could valuably be applied to other parts of the world: a comparable study for Europe, for instance, would be revealing. Their approach could also be extended to other parts of the air transport system, such as air traffic management, where the performance of skilled experts is also implicated in some airline accidents.
The main significance of this book is in its re-framing of the causes of airline accidents: the authors argue that, if we must continue to conceive of airline accidents in terms of deficiency, then that deficiency should be attributed to the overall air transport system. Such an approach can contribute to aviation safety by providing a foundation for improving equipment, training, procedures and organisational policy. In so doing, it is possible to reduce the frequency of `system accidents' and to devise adequate protection against the types of errors to which many, if not all, pilots - as well as many other experts - are vulnerable.