Proving mathematically that catastrophic top events cannot occur with probability greater than 10^-9 per flight hour.
Fault trees represent system failure as a top event broken down into intermediate events connected by AND, OR, and Priority-AND logic gates down to basic component failures (e.g., hydraulic seal leakage, transistor short).
Minimal cut sets represent the smallest combinations of basic events that cause the top event. To certify a Catastrophic condition, every cut set must contain at least two or three independent failures, proving zero single points of failure exist in the architecture.