Safety Analysis Methods for Complex Systems in Aviation

Each new concept of operation and equipment generation in aviation becomes more automated, integrated and interconnected. In the case of Unmanned Aircraft Systems (UAS), this evolution allows drastically decreasing aircraft weight and operational cost, but these benefits are also realized in highly automated manned aircraft and ground Air Traffic Control (ATC) systems. The downside of these advances is overwhelmingly more complex software and hardware, making it harder to identify potential failure paths. Although there are mandatory certification processes based on broadly accepted standards, such as ARP4754 and its family, ESARR 4 and others, these standards do not allow proof or disproof of safety of disruptive technology changes, such as GBAS Precision Approaches, Autonomous UAS, aircraft self-separation and others. In order to leverage the introduction of such concepts, it is necessary to develop solid knowledge on the foundations of safety in complex systems and use this knowledge to elaborate sound demonstrations of either safety or unsafety of new system designs. These demonstrations at early design stages will help reducing costs both on development of new technology as well as reducing the risk of such technology causing accidents when in use. This paper presents some safety analysis methods which are not in the industry standards but which we identify as having benefits for analyzing safety of advanced technological concepts in aviation

Particle Trapping in Estuarine Tidal Flows

Particle trapping in estuarine turbidity maxima (ETM) is caused primarily by convergent mean and/or tidal fluxes of sediment. The result is an approximately bell-shaped along-channel distribution of vertically integrated, tidal cycle mean suspended sediment concentration. Observations from the Columbia River estuary suggest that (1) strong two-layer or internal along-channel residual and overtide flows are generated by time-varying stratification and (2) correlations between the near-bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment. A new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process. Time changes in tidally averaged sediment concentration between two estuarine cross sections can be shown to be related to the divergence of the seaward, river flow transport; the divergence of velocity shear-sediment stratification correlations for the mean flow and each tidal constituent; and net erosion or deposition at the bed. Vertically integrated variables other than seaward river transport are absent from this integrated balance. Analysis of sediment fluxes using this balance supports the idea that internal residual and overtide circulations are primarily responsible for the landward sediment transport on the seaward side of ETM found near the upstream limits of salinity intrusion. The balance also shows that attempts to represent fluxes causing trapping of sediment in an ETM as a product of a time-mean, vertically integrated, along-channel gradient and a diffusivity inevitably lead to the appearance of countergradient transport and thus a negative diffusivity on the seaward side of the ETM. This result occurs because the trapping process is inherently nonlinear and at least two-dimensional and because a one-dimensional representation is physically unrealistic

Considerations on Aviation Standards for Simultaneous Independent and Dependent Parallel Approaches

Required Navigation Performance (RNP) procedures to parallel runways that include curved approaches offer many benefits to the flying public, airlines, and nearby residents on the ground. Fewer track miles are required during approach, thus enabling decreases in missed connections, fuel burn, emissions, and noise footprint. This paper documents research on independent and dependent RNP approaches to parallel runways. The goals are to provide recommendations to support the International Civil Aviation Organization (ICAO) rule changes and to promote the growth of these RNP-enabled procedures around the world. The paper will be structured as follows: After pointing out the benefits that curved RNP procedures provide at parallel runway environments, we will summarize and compare current ICAO and Federal Aviation Administration (FAA) rules for simultaneous approach operations as well as proposed revisions of ICAO’s guidelines. We conclude that current ICAO standards and their proposed revisions will not fully reflect the changes needed to achieve all of the benefits that curved RNP procedures can provide in parallel runway environments. Accordingly, we will identify areas within the guidelines that need to be extended for this purpose. We will then describe two methodologies to enable safe RNP procedures to parallel runways that include curved approaches. Those two methodologies are based on safety concepts that were developed for RNP-established procedures at Seattle and safety concepts developed for Frankfurt Airport. Finally, we will conclude with possible ways to extend ICAO’s guidelines based on these concepts and identify further aspects that need to be considered, such as the potential of nuisance Traffic Alert and Collision Avoidance System (TCAS) alerts