Public Release: 

Aviation And Turbulence: FAA And NCAR Continue Investigations

National Center for Atmospheric Research/University Corporation for Atmospheric Research

The FAA and NCAR explore a new detection and warning system for Juneau, Alaska, and tackle remote sensing and forecasting problems. Meanwhile the U.S. Navy seeks NCAR's help with choppy winds on high-speed vessels.

A State-of-the-Art Warning System for the Juneau Airport

BOULDER--Juneau, Alaska, may become the world's first airport to employ a new turbulence detection and warning system developed by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. Originally developed for Hong Kong's new Chek Lap Kok Airport, scheduled to open in fall 1998, the system alerts air traffic controllers and pilots to choppy winds at airports located near mountainous terrain.

With an eye to assessing the wind-shear problem at such airports, the Aviation Weather Research Program of the Federal Aviation Administration (FAA) is funding data gathering and analysis at Juneau and Colorado Springs, Colorado, this winter. NCAR has deployed an array of sensors for data gathering that could be the basis for a prototype turbulence warning system. NCAR's primary sponsor is the National Science Foundation.

"Turbulence alone doesn't bring planes down," says NCAR expert Larry Cornman, "but it may trigger a chain of events that results in a tragedy." In 1991 severe turbulence ripped an engine off a 747 cargo plane departing from the Anchorage airport. With difficulty the pilot managed to return to the airport safely. That same year United Flight 535 crashed on final approach into the Colorado Springs airport in the throes of a powerful windstorm. The National Transportation Safety Board did not find a probable cause for the Colorado Springs accident, but strong turbulent winds and a rudder problem are generally thought to be the most likely explanations.

"I call turbulence the silent problem of the aviation industry. People aren't dying from it, but uncomfortable flights and even broken bones are more common than people realize, especially for flight attendants," says Cornman. On average, a significant turbulence incident occurs every other day on a commercial flight somewhere in the United States. Records show planes suddenly dropping 200 to 300 feet vertically, hurling food carts up to the ceiling.

NCAR's turbulence programs may signal new awareness of a long-term problem. Last month representatives from the FAA, National Oceanic and Atmospheric Administration, several major airlines, and airline pilots' and flight attendants' associations met at NCAR to discuss the effects of turbulence on commercial aviation. Officials decided to set up a working group to solve the persistent problem of bumpy flights, flight attendants' injuries, and more serious incidents caused by mountain-induced turbulence. Cornman's "silent problem" may have found a voice.

The Juneau airport is especially challenging because takeoffs sometimes require a 180-degree turn inside a channel between an island and the mainland, both with steep terrain. Often the plane is being pummeled by high winds. To prevent any possibility of a crash, the FAA temporarily closed the airport's departure routes last fall and later reopened them with restrictions based on wind speeds measured by a network of anemometers in the area.

This winter NCAR scientists added two wind profilers, or vertically pointing Doppler radars, to the anemometer network to gather data to develop a real-time turbulence detection and warning system for Juneau. The ground-based profilers measure wind and turbulence at 60-meter height intervals up to 2 kilometers above the ground, updating every 30 seconds.

As in Hong Kong, the Juneau system would feature computer monitors in the control tower displaying real-time turbulence information (summarized from the wind profiler and anemometer data), which would then be relayed over radio to pilots landing or taking off. A more involved data collection program is also being planned for Juneau next year, using a research aircraft, three wind profilers, and a Doppler lidar (laser-based detection system).

With accurate warnings, pilots will know when it makes sense to avoid a particular turbulence structure, such as a rotor wind--a horizontal, tornado-like vortex that forms on the downwind side of a mountain. Although rotor vortex winds don't reach tornadic speeds, "pilots definitely don't want to find themselves entering a rotor near the ground," says Cornman.

NCAR has a long history of helping to develop airport warning systems for the FAA. NCAR, along with other federally funded research centers, participated in a ten-year project to develop the Terminal Doppler Weather Radar, which alerts air traffic controllers to dangerous wind shear and microbursts. Today the TDWR is operating or scheduled for deployment at about 50 airports around the country. Cornman expects the current development of a system for turbulence detection and warning to take only three to five years, if funded.

New Work on Forecasting and Detecting Turbulence

Developing a real-time warning system is just one part of NCAR's wide-ranging turbulence research program. Cornman and colleagues are also working on improving turbulence forecasting and remote sensing and on gathering turbulence measurements from commercial aircraft, both projects funded by the FAA. The U.S. Navy has hired the team to characterize turbulent winds over helicopter landing pads on fast-moving Navy ships.

Numerical computer models are an essential tool for better diagnosis and forecasting of turbulence, and these in turn could lead to more efficient aircraft routing. The Hong Kong system already includes a forecast modeling component, and one may eventually be incorporated into U.S. detection systems as well.

To improve remote sensing of turbulence, the NCAR team is working on new algorithms, or mathematical problem-solving procedures, for using data from the National Weather Service's WSR-88D (formerly known as NEXRAD) radar system. Accurate detection of turbulence by the WSR-88D and other instruments would improve real-time warnings for pilots and help scientists verify turbulence forecasts.

Cornman is also heading a project to develop software that will turn the aircraft itself into a turbulence-sensing platform. The software uses existing on-board sensors and computers to measure and analyze turbulence as the aircraft flies through it. United Airlines is installing the prototype on about 200 aircraft during 1997, and several other airlines are interested in testing it.

Not only airplanes face the problems of chaotic winds. The U.S. and U.K. navies have enlisted NCAR's help in understanding air flow around destroyers and other large ships as they cruise the seas at high speeds. NCAR scientists will help the Navy characterize these flow fields by analyzing data from on-board, state-of-the-art lidars built by Lockheed-Martin. This understanding will then be incorporated into vessel design, especially to aid helicopters landing on windy decks.

This research is sponsored by the National Science Foundation through an interagency agreement in response to requirements and funding by the Federal Aviation Administration's Aviation Weather Research Program. NCAR is managed by the University Corporation for Atmospheric Research under sponsorship by the National Science Foundation.


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