A Windshear Hazard Index

In context of aviation science, windshear refers to a change in wind speed or direction experienced by an airplane over a particular distance or length of time. An aircraft exposed to a hazardous level of windshear may suffer a critical loss of airspeed and altitude, thus endangering its ability to remain airborne. In order to characterize the hazard of windshear to aircraft, a nondimensional index was developed based on the fundamentals of flight mechanics and our understanding of windshear phenomena. This paper reviews the development and application of the Bowles F-factor, which is now used by onboard sensors for the detection of hazardous windshear. It was developed and tested during NASA/FAA's windshear program and is now required for FAA certification of onboard radar windshear detection systems. Reviewed in this paper are: 1) definition of windshear and description of atmospheric phenomena that may cause hazardous windshear, 2) derivation and discussion of the F-factor, 3) development of the F-factor hazard threshold, and 4) its testing during field deployments.