RAP associate scientist Tenny Lindholm used his experience as a pilot to make connections with the avionics company incorporating the software and with United Airlines. United expects to deploy the new system on more than 200 aircraft over the next six months.
Until now, the only data on turbulence--the sudden, invisible gusts that buffet a plane and its passengers--have come 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 Larry. Part of that cost comes from testing new equipment to ensure that it doesn't 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 Larry. "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 (taken from the plane's vertical accelerometer) while accounting for its weight, air speed, altitude, and whether the plane is on autopilot or not. Human or automated pilot response to turbulence--trying to damp out its effects--proved to be an important element in the equation.
|In tandem with the in-situ turbulence sensing program, RAP is working on prototype displays for eventual use in helping pilots steer clear of turbulence. This image and the one below address the horizontal and vertical dimensions, respectively. The cockpit display above allows pilots to refine their original choice of flight path from Denver (DEN) through Salina, Kansas (SLN). The optimal wind route takes into account turbulence information in two ways: "Strategic Forecast," the cross-hatched area calculated and issued to the pilot pre-flight, and "Tactical Situation," a more specific, shorter-term forecast issued en route. The software uses these to calculate a path, the strategically planned route, that angles to the north, or left, of the turbulence-compromised route. (Illustration courtesy RAP.)|
Larry and colleagues 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 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), as well as to the NWS Aviation Weather Center in Kansas City, Missouri. Tenny expects Delta, Northwest, and American to join the project during the next two years.
|This display shows the same scenario as above, but in a vertical cross section. The initial flight route from Denver to Kansas City, Missouri (MKC), which appears as the lower line, is chosen based on wind and temperature data alone. Turbulence is detected near Hill City, Kansas (HLC), as indicated by the light-shaded area. An optimal alternative route would take the aircraft above the strongest core of the jet stream (darkest shading). This would reduce its fuel efficiency but would bypass the turbulence. (Illustration courtesy RAP.)|
Larry expects the new in-situ reporting system to make a real difference to researchers. "We're not just quantifying turbulence by labeling it 'level 3 on a scale of 1 to 5,' we're generating a turbulence measurement that's already well established in the scientific community."
With 200 United aircraft reporting once a minute from flights over the entire continental United States during the next several years, plus hundreds more possibly joining the system from other airlines, Larry says the potential is there to gather a lot of data. "I think people are excited about having something like this. It will really help us map the atmosphere in terms of turbulence."
As more aircraft are brought on line, Larry 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," Larry explains. One goal is a cockpit weather display (see prototype pictured on pages 1 and 2). He expects turbulence to join icing and convective weather on a cockpit weather menu within the next five years.
Before the RAP project, no one had tried to use an inverse problem-solving method incorporating the current list of variables in quite the same way. A different method has been in use in Australia for the last few years. The International Civil Aviation Organization (ICAO) will compare results from the U.S. and Australian detection programs with the goal of establishing an international standard for turbulence measuring and reporting. Zhenya Gallon