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You need to bear in mind that safety assurance in aviation relates to the prevention of catastrophic events which kill many people, and thus provides considerable redundancy of systems. In medicine, problems such as malfunctioning of anaesthetic equipment will, at worst, kill one or two. Another relevant factor is that help, replcement equipment, expert assistance and so on are out of reach to the crew of an aircraft in flight, whereas in a medical facility they are usually readily available.