ABSTRACT
The question of why human error accidents occur has been addressed by Reason with his concept of systemic failures. Rasmussen looked at how such errors occurred, with his classification of errors as deficient skill, misapplication of rules, and lack of knowledge of the operating system. To achieve the goal of 'Diverting to an Alternate', the pilot might decide to climb only to minimum safe altitude, perhaps minimising traffic delays, or to climb until the descent path is intercepted, often the most economical way. There are likely to be some errors after the initial event, as the pressure builds up, but it is the triggering error which gives the pilot the opportunity to make the subsequent errors. O'Hare et al analysed the errors in quite a number of accident reports. It appears that major accidents usually stem from faulty decisions, while faulty implementation tends to result in minor accidents.
