Dealing adequately with technical uncertainties

Statistics, RAMS & Quality Management
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Event Tree Analysis

Event tree analysis begins where fault tree analysis ends: At the top event. While fault tree analysis is used for assessing potential dangerous scenarios within the responsibility of a safety function, event tree analysis works similar, however for potential consequences outside the responsibility of the safety function.
The structure of event trees is a reversed fault tree structure: On a time axis, fault trees branch out into the past while event trees branch out into the future.
The twin engine aircraft example may give some insight (see also fault tree analysis and reliability block diagram).



This example is a little bit different compared to the twin engine examples in other paragraphs. Instead of a crash landing, its starting point is a single engine failure. This is only for didactical reasons. Moreover, fault trees with top event = crash landing don't exist in practice, whereas trees with top event = engine failure do exist. 

Event tree calculation yields the probability distribution over various consequences. In the above example, the result may look like this:

P(regular landing) given one engine failed = 0,99999
P(successful emergency landing) given one engine failed = 0,000005
P(crash landing) given one engine failed = 0,000005

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