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Perspectives: Tracking Down Turbulence

By James Watson and Kathy Barnsdorf | September 1, 2003
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Doppler windshear radar systems on board airliners may soon be used to predict turbulence associated with stormy weather as well, thanks to research done by NASA’s Aviation Safety and Security Program (AvSSP). NASA, the Federal Aviation Administration and industry are working together to develop a commercial aircraft sensor with an 80 percent probability of detecting severe storm-related and clear-air turbulence 30 seconds to two minutes before an encounter.

To combat the problem, engineers and scientists first worked to better understand what produces rough air. Atmospheric turbulence is caused by warm air and cold air mixing together, which generates strong vertical velocities of updrafts and downdrafts.� It is difficult to predict, but researchers have identified contributing factors: convective storms (as far as 50 miles away from visible clouds even in clear air), jet stream, mountain wave, and cold or warm fronts.

NASA has partnered with AeroTech Research (USA), Aviation Cabin Safety Specialists, the Federal Aviation Administration (FAA), the National Center for Atmospheric Research, North Carolina State University and Research Triangle Institute to develop, enhance and test a system to detect and predict storm-related turbulence–the Turbulence Prediction and Warning System (TPAWS). The team is led by NASA’s Langley Research Center in Hampton, Va., with participation from two other NASA facilities: Dryden Flight Research Center in Edwards, Calif., and Glenn Research Center in Cleveland, Ohio.

TPAWS is an enhanced turbulence detection radar system that detects atmospheric turbulence by measuring the motion of moisture in the air. It is a software signal processing upgrade to existing predictive wind shear systems that were developed at NASA Langley in the 1990s and are on many modern airplanes. The technology includes algorithms that are designed to predict turbulence in front of the airplane and then indicate how hazardous the turbulence is to the airplane. This means that different sizes of aircraft will receive different warnings from the same�turbulence event.����

Researchers have tested TPAWS on board a NASA Boeing 757 research aircraft, based at NASA Langley. NASA and its partners equipped the Airborne Research Integrated Experiments System (ARIES) flying laboratory with the experimental radar system and then went searching for thunderstorms over an eight-week period last year.

To see how well the enhanced radar performed, the B757 and its crew had to find the kind of bumpy weather most airline passengers find uncomfortable. ARIES flew within a safe distance of storms, so researchers could experience the turbulence and compare what the radar predicted versus what the plane encountered. ARIES flew 13 research missions. The jet would leave NASA Langley and fly to areas where thunderstorms were predicted east of the Mississippi. NASA research pilots circled the thunderstorms repeatedly to subject the plane to rough air.

Inside the B757, researchers at test stations recorded conditions and also alerted the pilots when and where they were likely to encounter turbulence and how much.

After one particularly severe patch of turbulence, one of the NASA research pilots said his confidence in the enhanced radar had "gone up dramatically," since the plane’s weather radar was showing nothing at the same time the turbulence display was indicating rough skies ahead.

NASA plans future flight tests of TPAWS radar and says the technology should be ready for airliners within a couple of years. This summer the system won a NASA "Turning Goals into Reality" award as the best technology developed and tested in 2002.

Atmospheric turbulence is the leading cause of in-flight injuries to airline passengers and flight crews. FAA statistics show that 98 percent of those injuries happened because people were not wearing seat belts. An alert of impending rough air would give pilots time to warn passengers and flight attendants to buckle up. Turbulence is not only hazardous, it also costs the airlines money and time, in the form of rerouting and late arrivals.

To tackle turbulence, the NASA Aviation _Safety and Security program also is developing better forecasting techniques, drafting a turbulence characteristics scale, and studying methods to minimize turbulence effects.

AvSSP is a partnership between FAA, aircraft manufacturers, airlines and the U.S. Department of Defense. This partnership supports a national goal to reduce the fatal aircraft accident rate by 80 percent in 10 years. Researchers at four NASA field installations are working to develop advanced, affordable technologies to make flying safer: Langley; Ames Research Center at Moffett Field, Calif.; Dryden; and Glenn. For more information on the NASA Aviation Safety and Security Program, check the Internet at

James Watson is acting manager for Turbulence Prediction and Warning Systems, and Kathy Barnsdorff is a public affairs specialist, at NASA’s Langley Research Center.

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