Quick-reference calculators for everyday safety-assessment work — severity to DAL, failure probability, and fault-tree gate probability. They run right here, no sign-up. The full traceable versions live inside Safety Lab Aero.
Map a failure-condition severity to its top-level Development Assurance Level and the quantitative probability target for transport-category aircraft (CS/FAR-25 · AC 25.1309).
Top-level FDAL from severity. Under ARP 4754A, independent members of a development-assurance set can be assigned lower IDALs — the full tool walks that allocation and keeps it traceable. Part-23 targets scale by certification level/class.
Convert a constant failure rate λ and an exposure time t into a failure probability over that interval. For small λt, P ≈ λt.
Combine basic-event probabilities through a single gate. AND multiplies (independent events); OR uses the complement rule 1 − ∏(1 − pi).
Single-gate combination assuming independence. Real cut-set / minimal-cut-set evaluation across a full tree (with shared events and common cause) is what the deterministic engine in the app does.
Inside Safety Lab Aero, every number you see here is connected to its failure condition, its fault tree, and its requirements — the golden thread — so changing one updates the rest. Grounded in ARP 4761A / 4754B.
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