A numerical large-eddy simulation model is currently being used to quantify aircraft wake vortex behavior with meteorological observables. The model, having a meteorological framework, permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, and humidity. The addition of grid-scale turbulence as an initial condition appeared to have little consequence. Results show that conventional nondimensionalizations work very well for vortex pairs embedded in stably stratified flows. However, this result is based on simple environments with constant Brunt-Vaisala frequency. Results presented here also show that crosswind profiles exert important and complex interactions on the trajectories of wake vortices. Nonlinear crosswind profiles tended to arrest the descent of wake vortex pairs. The member of the vortex pair with vorticity of same sign as the vertical change in the ambient along-track vorticity may be deflected upwards.

to rapid wake decay or drift away from the flight path.In table 1, small aircraft are those with maximum takeoff weights less than 18,598 kg (41,000 pounds), large are those aircraft between 18,598 and 115,668 kg (41,000 and 255,000 pounds) and heavy are over 115,668 kg (255,000 pounds). During visual conditions the separation responsibility is passed to the pilots, who use their knowledge of weather conditions, lead aircraft type, and lead aircraft flight path to effectively selfseparate from wake encounters. In many situations the resulting spacing is less than would be required in instrument operations. The AVOSS is designed to structure this process and minimize the difference in aircraft spacing between visual and instrument operations. FollowingLeading ( NM).The basic AVOSS architecture is unchanged from previous descriptions t'2'3'4 and shown in figure 1. This architecture supports the basic functional requirement of calculating the separation required to prevent aircraft encounters with wake vortices, given the current and expected meteorological parameters. The meteorological subsystem uses sensors and modeling techniques to describe the vertical profiles of the wind, turbulence, and temperature from the surface to the glide slope intercept altitude. A statistical description of relevant variables is provided to minimize spatial variations and permit prediction of the worst-case wake behavior that may occur during an operational time period. The wake predictor uses this weather profile and descriptions of the aircraft fleet at the airport to predict wake drift rate, sink rate, and decay rate for each modeled aircraft type. The wake behavior is compared to predefined safety corridor dimensions and a wake demise definition to derive required aircraft separation intervals.Wake vortex sensors are used to verify that the wakes are behaving within the range of predicted values.The AVOSS development is focused on a year 2000 demonstration, in a relevant airport environment, of a real-time wake vortex spacing system. The system demonstration will include all systems shown in figure 1, up to but not including the ATC interface. The system integration element will link all subsystems for automated system operation. Actual aircraft spacing reductions will not be made as an element of the demonstration. The objective of the development effort and demonstration is to bring the maturity levels of all systems to the point that the concept can be proven in an operational environment, with all variables present, and that the system is ready for handoff to the FAA and industry for operational test bed development. The system to be demonstrated will emphasize the scientific validity of the weather profile measurements and wake predictions, and not the final engineering required for prototype operational equipment. As such, certain features such as system self-test and ATC interfaces may be absent or implemented only to the degree required for demonstration of the system concept. A detailed description of AVOSS Version 1 ...

The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements during instrument meteorological conditions through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations (RSO) subelement at the NASA Langley Research Center is developing an Aircraft Vortex Spacing System (AVOSS). AVOSS will integrate the output of several inter-related areas to produce weather dependent, dynamic wake vortex spacing criteria. These areas include current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, real-time feedback of wake vortex behavior from sensors, and operationally acceptable aircraft/wake interaction criteria. In today's ATC system, the AVOSS could inform ATC controllers when a fixed reduced separation becomes safe to apply to "large" and "heavy" aircraft categories. With appropriate integration into the Center/TRACON Automation System (CTAS), AVOSS dynamic spacing could be tailored to actual generator/follower aircraft pairs rather than a few broad aircraft categories.

A distinguishing feature of the ninth century is the amount of precious metal that has survived from it. Some of this comes from hoards, for in contrast to the eighth century there are several with both coins and objects, as well as some only with coins and some only with objects. The latest coin in a hoard provides no more than the earliest possible date at which it could have been deposited, but at least that is a fixed point in one direction, and its owner was unlikely to keep a store of coins for long without occasionally taking some out or putting others in. Objects in hoards, of course, may always include some treasured heirlooms, as may furnished graves, but at least perceived similarity to works in other media is not their only dating criterion. A few objects can be dated because they have an identifiable name on them. A gold and niello ring inscribed Ethelwulf R[e]x at the bottom of the bezel associates it with King Aethelwulf, ruler of Wessex from 839 to 858 (Fig. 4.1, right). The ring was not necessarily made for him to wear himself, but for him to give to a follower as a permanent reminder of the service owed to its donor, though a Beowulf seeking a ‘generous ring-giver’ might not have thought its inscription sufficient compensation for its modest weight. Alternatively, it could have acted like a seal, to accompany a royal messenger and validate that his news or instructions came from the king; or have been used as a guarantee of a land donation and a physical reminder of the event at which the grant had been made. That might have been the reason why the name of Queen Aethelswith was added to the back of another gold ring, thus associating it with Aethelwulf’s daughter, who was queen of Mercia from 853 to 874 (Fig. 4.1, left). The inscription may have been an afterthought, needed when the ring was used for an unanticipated purpose. A third explanation is that both rings were baptismal; above Aethelwulf’s name are two birds at the Fountain of Life, and the bezel of Aethelswith’s ring has the Lamb of St John the Baptist.

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