Enhanced Descent Wind Forecast for Aircraft Facilitation of Continuous Descent Arrivals with Improved Efficiency and Predictability by the use of Tailored Descent Wind Forecasts

In order to perform an efficient and predictable Continuous Descent Arrival (CDA), it is critical to accurately determine the geometric descent path that can be flown with idle thrust for the selected Cost Index. To build the geometric descent path, the aircraft's Flight Management System (FMS) needs to be aware of the forecast winds during the descent. Inaccuracies in these forecast winds can lead to a geometric path that cannot be flown as an idle-thrust CDA; (manual) energy management is required to maintain the path at the cost of loss in efficiency (fuel burn). Secondly, inaccurate forecast winds impact on predictability as they reduce the accuracy of trajectory predictions made by the FMS. This inaccuracy is caused by both the error in the forecast wind, and the deviations from the target descent speed as result of maintaining the inaccurately built geometric path at idle thrust (either too steep or too shallow). Design constraints of current FMSs restrict the number of flight levels at which forecast data can be entered. This limits the definition of the wind profile for the complete descent path. Airservices Australia has developed a tool that tailors the wind forecast for a specific arrival using an improved resolution forecast provided by the Australian Bureau of Meteorology. Flight trial results indicate that the tailored descent forecasts can provide the FMS with a better representation of the wind profile on descent leading to improved predictability. However, no benefits to aircraft operating efficiency were observed. The research found consistent large deviations from the target speed while performing a path managed descent (10kts slow on average); these deviations could however not be correlated to the error in the forecast. As non-idle thrust settings were often required because of these large deviations, it is believed any efficiency benefits of the tailored descent forecasts are obscured.