NCAR Research Turns Commerical Aircraft Into Turbulence Sensors

With funding from the Federal Aviation Administration (FAA), NCAR scientist Larry Cornman and his colleagues have created software that works with an aircraft's existing equipment to measure and report in-situ (in-flight) turbulence once every minute. United Airlines expects to deploy the software on more than 200 aircraft over the next six months. The data will be used to create turbulence forecasts to help pilots steer clear of bumpy air. NCAR's primary sponsor is the National Science Foundation.

Until now, the only data on turbulence--the sudden, invisible gusts that buffet a plane and its passengers--came from pilot reports of bouncy or choppy air. "If we'd tried to come up with a new sensor to load onto the aircraft, it would have been too costly," explains Cornman. Part of that cost comes from testing new equipment to ensure that it does not affect flight operations. "So we looked for a way to use sensors, computers, and communications systems that were already on board, without interfering with their normal functions." Instead of measuring turbulence directly, the researchers use the aircraft's response to turbulence to deduce its magnitude.

"We're solving an inverse problem," says Cornman. "If I measure what the aircraft's doing, I can infer what the turbulence must have been." The result is an in-situ turbulence algorithm, or mathematical problem-solving procedure, that uses measurements of how much the aircraft is bouncing up and down while accounting for its weight, air speed, altitude, and whether the plane is on autopilot or not.

The algorithm is incorporated into software installed by Allied Signal, Inc., within Allied's onboard flight management system and aircraft condition monitoring system. The data are then transmitted to an FAA/National Weather Service (NWS) data base.

On average, a significant turbulence incident happens every other day on a commercial flight somewhere in the United States. The result can be everything from spilled food trays to broken bones for flight attendants and passengers not buckled into their seats. In 1991, severe turbulence tore the engine off a 747 cargo plane departing the Anchorage airport. While a cause for the crash of United Flight 535 on final approach to Colorado Springs airport in 1991 has never been determined, turbulent winds and a rudder problem are thought to be the most likely explanations.

Cornman and other scientists will use the data compiled on the FAA/NWS data base to create a turbulence detection product--a view of flight tracks showing what all of the aircraft in a given region have measured in a 30-minute period. That flight track information will be provided to United Airlines (and to other airlines as they become participants in the future), as well as to the NWS Aviation Weather Center in Kansas City, Missouri.

As more aircraft report more data, Cornman expects forecasting products to improve to the point that "nowcasting," or turbulence warnings in real time, will be possible. "Having such a comprehensive and accurate data base will really boost our development of new forecasting tools," Cornman explains.

The International Civil Aviation Organization (ICAO) will compare results from the U.S. in-situ turbulence detection program to ongoing research at the Australian Bureau of Meteorology. ICAO's goal is an international standard for turbulence measuring and reporting.

NCAR is managed by the University Corporation for Atmospheric Research.

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Writer: Zhenya Gallon

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