Fault Tree Analysis (FTA)

The top of the tree is a single failure, such as a payment system going offline. Beneath it, branches show the events that could lead there. An AND gate means all inputs must occur together. An OR gate means any one is enough. Following branches down reaches basic events, like a power cut or a software bug, which cannot be broken down further. Where failure rates are known, the tree can produce a probability for the top event, and it shows which single faults or small combinations matter most. Engineers developed it for aerospace and nuclear safety, and it now supports reliability, safety and cyber studies. It handles one outcome at a time, so many trees are needed for a wide study. Analysts read the tree for single points of failure, which show up as one basic event feeding the top through OR gates alone.

An airline wants to know why an engine warning might not reach the crew. The tree shows that a sensor fault OR a display fault is enough on its own, while a failure of the backup alert needs a power loss AND a software error together. The sensor path looks likeliest, so the team adds a second sensor.