Government-Industry Collaborative Investigations of In-Cloud Versus Out-of-Cloud Turbulence

Commercial and general aviation aircraft frequently encounter unexpected atmospheric turbulence. These encounters often result in rerouting of flights, and though rarely fatal, can sometimes even result in serious injury to aircraft occupants or aircraft damage. According to the Federal Aviation Administration (FAA), turbulence is the leading cause of injuries to passengers and flight attendants in non-fatal accidents.¹ During the years 1998-2013, US air carriers had 432 significant turbulence incidents or accidents, with 225 serious injuries.² In addition, the cost to air carriers of these injuries, equipment damage and maintenance/inspection, or rerouting is substantial. Moreover, rerouting of flights due to reported or forecast turbulence can significantly reduce National Airspace System (NAS) capacity.

Beginning in the 1990’s, the FAA’s Aviation Weather Research Program (AWRP) began managing and funding research efforts at the National Center for Atmospheric Research (NCAR) to improve turbulence forecasting and reporting capabilities within the NAS. Along with a gridded turbulence forecast product, Graphical Turbulence Guidance (GTG), a turbulence detection and reporting algorithm was developed for use on commercial aircraft. This on-board algorithm produces an aircraft-type independent turbulence intensity metric, Eddy Dissipation Rate (EDR), which describes the turbulent state of the atmosphere, and is the International Civil Aviation Organization’s (ICAO) standard for turbulence reporting.

Several United States commercial air carriers currently utilize the EDR reporting capability. Southwest Airlines (SWA), for example, has recently expanded its EDR reporting capability to nearly 700 aircraft. While the additional in situ turbulence data is valuable for turbulence forecast models, SWA aircraft have the additional capability of atmospheric moisture measurements through the Water Vapor Sensing System II (WVSS II). Many SWA aircraft have both the EDR and WVSS II reporting capability.

This capability provides the research community with a new, unique data set for studying in-cloud versus out-of-cloud turbulence. For the first time, simultaneous recordings of water vapor and turbulence are available from thousands of encounters, allowing robust statistical evaluations. It is with this in mind that the FAA, in collaboration with SWA and NCAR, has embarked on a study of the relationship between turbulence and clouds. We believe the new data will allow us to better define and characterize the relationship between clouds and convective and non-convective turbulence.

This paper will present the preliminary results from the FAA-funded study, and will address potential applications in the aviation industry.

¹http://www.faa.gov/passengers/fly_safe/turbulence/

²NTSB Briefing presented at Turbulence Workshop, Washington DC, September 3, 2014