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 ...