Federal Radionavigation Plan-pie in the sky for civil aviation?

The Federal Radionavigation Plan states that all present navigation and landing guidance facilities will be retired starting in 2005, and full dependence for these functions will be placed on augmented GPS. Once this is implemented, civil aviation will be totally vulnerable to terrorist jamming of the GPS signals over wide earth areas with widespread disruption of air traffic and potential disasters. It has become apparent that the use of GPS/GNSS is complex and expensive for the required civil aviation functions. It is clear that a different system form is needed for civil aviation, a redundant satellite/ground based system that will prevent it from being a jamming target while providing ATC surveillance, area navigation, collision warning/avoidance, high-speed data link and Category I landing guidance globally, plus precision Category III guidance in the terminal areas as needed. Such a system will be described     

How Engineers Can Conduct Cost-Benefit Analysis for PHM Systems

Individuals who work in the field of Prognostic and Health Management (PHM) technology have come to understand that PHM can provide the ability to effectively manage the operation, maintenance, and logistic support of individual assets or groups of assets through the availability of regularly updated and detailed health information. Naturally, prospective customers of PHM technology ask: "How will the implementation of PHM benefit my organization?" Typically, the response by individuals in the field is: "Anecdotal evidence indicates that PHM decreases maintenance costs, increases operational availability, and improves safety." This information helps the prospective customer understand the practical benefits of the technology, but that customer stills needs more information to justify their investment in the technology. The customer needs a calculated return on investment (ROI) figure for their particular asset that provides financial assessment of the benefit of the investment. The data, time, and expertise required to conduct a rigorous cost benefit analysis makes the effort seem daunting to the average engineer with little to no fimancial analysis training. The reality is that with a cursory understanding of the asset operation, maintenance, and logistic issues, a useful cost-benefit analysis can be conducted by engineers without business school training. Our purpose herein is to provide a general methodology for conducting a preliminary cost-benefit analysis that calculates an ROI for PHM implementation. We discuss the general types of information needed for the analysis, the quantifying of expected benefits, and the types of supporting data required to validate the benefit assumptions as well as an outline for the costing of PHM technology.     

Quickest detection for sequential decentralized decision systems

Quickest detection procedures are techniques used to detect sudden or abrupt changes (also called disorders) in the statistics of a random process. The goal is to determine as soon as possible that the change occurred, while at the same time minimizing the chance of falsely signaling the occurrence of a disorder before the change. In this work the distributed quickest detection problem when the disorder occurs at an unknown time is considered. The distributed local detectors utilize a simple summing device and threshold comparator, with a binary decision at the output. At the fusion center, the optimal maximum likelihood (ML) procedure is analyzed and compared with the more practical Page procedure for quickest detection. It is shown that the two procedures have practically equivalent performance. For the important case of unknown disorder magnitudes, a version of the Hinkley procedure is also examined. Next, a simple method for choosing the thresholds of the local detectors based on an asymptotic performance measure is presented. The problem of selecting the local thresholds usually requires optimizing a constrained set of nonlinear equations; our method admits a separable problem, leading to straightforward calculations. A sensitivity analysis reveals that the resulting threshold settings are optimal for practical purposes. The issue of which sample size to use for the local detectors is investigated, and the tradeoff between decision delay and communication cost is evaluated. For strong signals, it is shown that the relative performance deteriorates as the sample size increases, that is, as the system cost decreases. Surprisingly, for the weak signal case, lowering the system cost (increasing the sample size) does not necessarily result in a degradation of performance