Renata Radziszewska

2025-01

AI-assisted FTA review tool — collaborated with AI team on a prototype LLM tool that reviews FTA logic for common errors (missing gates, cut set coverage, unmitigated single-point failures). Provided labeled FTA review examples as training data.

Challenge: LLM FTA review missed subtle single-point failures in nested fault trees — it correctly identified obvious unmitigated failures but failed to trace common cause failures through three levels of fault tree hierarchy. Required defining explicit traversal depth requirements in the tool specification.

Learned: AI FTA review tools must be tested specifically for multi-level fault tree traversal. Single-level pattern matching is insufficient for real fault trees — common cause failures and shared basic events must be tracked across the full tree depth to catch all single-point failure vulnerabilities.

2024-05

Flight control system SSA — integrated FTA results from PSSA with component-level failure data from suppliers to compute failure condition probabilities. Verified compliance with all Catastrophic (<10^-9/fh) and Hazardous (<10^-7/fh) probability requirements.

Challenge: One Catastrophic condition ('Loss of Pitch Control') had a computed probability of 2.4×10^-9/fh — non-compliant against the 10^-9 requirement. Required architecture redesign to add a third independent pitch control path, increasing system weight by 14 kg.

Learned: SSA compliance checks must be iterative throughout FCS architecture development, not a single late-stage computation. Discovering a non-compliant Catastrophic failure condition probability late in design when supplier FMEA data is available forces last-minute architecture changes — much more expensive than early PSSA-guided architecture selection.

2023-10

Fuel system PSSA — fault tree analysis for 8 Catastrophic fuel system failure conditions including fuel exhaustion, fuel tank explosion, and ETOPS fuel planning failure. Derived system-level safety requirements for fuel quantity sensing redundancy.

Challenge: The fuel exhaustion fault tree had a common cause event (flight crew error in fuel planning) that was difficult to quantify — crew error rates are poorly characterized for ETOPS operations. Required using the AMC 25.1309 conservative crew error rate and formally documenting the uncertainty.

Learned: Human error probability in safety FTA must use published, conservative reference values from AMC/AC unless specific human factors study data is available. Using internal estimates without regulatory backing will be rejected by DER during SSA review.

2023-03

Functional Hazard Assessment for the propulsion system — identified and classified 47 propulsion failure conditions from catastrophic to no-safety-effect. Established probability requirements for each Major, Hazardous, and Catastrophic condition per CS-25.1309.

Challenge: Classifying the severity of 'Loss of Thrust Asymmetry Protection' was contentious — operations and flight dynamics engineers disagreed on whether this was Hazardous (10^-7) or Major (10^-5) depending on the flight phase and aircraft configuration. Required a dedicated cross-functional review to reach consensus on the classification rationale.

Learned: FHA severity classification for failure conditions that span multiple flight phases requires explicit phase-by-phase assessment. A failure that is Major during cruise may be Catastrophic during approach — the FHA must document the worst-case phase classification and the rationale for it.