Aircraft performance in a JAWS microburst

Abstract

A dangerous sequence of events (headwind/downdraft/tailwind) occurs when an aircraft penetrates a microburst at low levels. A prime objective of the Joint Airport Weather Studies (JAWS) project was to quantify the event so that realistic wind shear profiles would be available for computer and manned-flight simulation of aircraft performance in hazardous winds. The three-dimensional wind components of a microburst have been measured with the high-resolution dual-Doppler radars of the JAWS project conducted by the National Center for Atmospheric Research. A six-degrees-of -freedom aircraft dynamics computer program with a simple automatic control logic to simulate an aircraft flying through the microburst has been developed. Aircraft performance for 26 simulated flights through the microburst has been calculated in this paper. The flight-path deterioration parameter (FPDP) concept and the low-level wind shear alert system (LLWSAS) concept were investigated relative to the 26 simulated flights. Appraisal of the effectiveness of the FPDP and LLWSAS is given based on the simulated results. The vertical wind speed component is found to be an important parameter in the detection of hazardous wind shear. A dimensionless parameter formed from the horizontal shear of the horizontal wind speed, vertical wind speed, and height above ground is described as a possible detection signal. Correlation of this with poor flight-path control is shown. It is concluded that further analysis of the JAWS data is necessary to provide insight into the critical wind shear severity thresholds and the scales of motion that lead to dangerous aircraft responses.