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5 Improvements to the TARAM Process
Pages 29-39

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From page 29...
... the causal and functional relationships between system-level events in the event trees and their underlying subsystems and components/equipment. Similarly, 14 CFR 25.1309 fault trees or other probabilistic analysis could be integrated with the causal chains in TARAM.
From page 30...
... methodology7 to integrate event trees and fault trees with simulation models of underlying failure mechanisms by generating a probabilistic interface equipped with key functions to convert the simulation data to the PRA inputs considering uncertainty analysis and dependent failure analysis. The I-PRA methodology models the underlying causation using a system performance simulation rather than translating the system behavior to a probabilistic graphical model as done in IRIS.
From page 31...
... decision-making practice accounts for the common cause failure (CCF) as one of the qualitative decision criteria (Table 9, "Qualitative Safety Criteria," in the FAA Seattle ACO Branch Transport Airplane Safety Manual)
From page 32...
... Recommendation 4: Within 6 months of receipt of this report, the Federal Aviation Administration should evaluate and document its approach to the use of quantitative common cause failure analysis, performed under probabilistic risk assessment, to determine its applicability for the continued opera tional safety process. INCORPORATING HUMAN RELIABILITY ANALYSIS IN THE TARAM PROCESS On the human side, recognition needs to be given to the fact that flight, cabin, and maintenance crew all play an important and interconnected role in maintaining safe operations.
From page 33...
... 19  U.S. Nuclear Regulatory Commission, 2006, Evaluation of Human Reliability Analysis Methods Against Good Practices, NUREG-1842, Washington, DC: Office of Nuclear Regulatory Research.
From page 34...
... Methods to study their combined effect are necessary to understand not only the primary but also the secondary, compound, or system-level risk. Assessment of the current TARAM methodology indicates that the modeling techniques for probabilistic assessment of human reliability and software reliability need to be aligned with current standards.
From page 35...
... This group could also be responsible for the above recommended activity. INCORPORATING SOFTWARE RELIABILITY ANALYSIS IN THE TARAM PROCESS Until now, efforts to improve software reliability on commercial airplanes mainly centered around software faultavoidance and fault-tolerant technologies.34 These fault-avoidance technologies are common in software reliability engineering as they rely on a compliance with formal development guidelines, design requirements, and testing and validation procedures to reduce ambiguity, uncertainties, and potential software faults.
From page 36...
... The two methods were then combined to develop a Bayesian updating algorithm in which a prior distribution of the software error probability is first developed via the BBN approach (or using a non-informative prior distribution) , and the test-based method is then used to generate data needed for the Bayesian updating.41 To incorporate software reliability into the current PRA frameworks, software functions or components are modeled as events on the PRA model's event trees and/ or fault trees.
From page 37...
... compliance for use in conducting the in-service safety process. These methods and tools should take advantage of Development Assurance Level assessments of software/airborne electronic hardware, Fault Tree analysis, and other probabilistic risk assessment methodologies that support software reliability analyses.
From page 38...
... The COS decision-making practice, documented in the Seattle ACO Branch Transport Airplane Safety Manual, includes no guidance on uncertainty analysis but provides a limited-scope sensitivity analysis to study the risk output change when any of the TARAM inputs are varied in a predefined manner. For instance, the current approach to calculate the peak individual flight risk for an issue under study in the constant failure rate analysis (Section 2.2 of the Seattle ACO Branch Transport Airplane Safety Manual)
From page 39...
... in a one-at-a-time manner. Recommendation 7: Within 12 months of receipt of this report, the Federal Aviation Administration should establish and document guidance to account for the uncertainties associated with inputs and models used in the Transport Airplane Risk Assessment Methodology process.


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