Aircraft test autumn winds of Juneau

A passenger-less Alaska Airlines 737 will make numerous landings at the Juneau Airport during the next few weeks as scientists collect data to help pilots from Juneau to Reno better predict dangerous turbulence and wind shear.

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Since a 1996 incident in which two flight attendants suffered serious injuries when a jet above Juneau encountered severe turbulence and rolled on its side, scientists from the National Center for Atmospheric Research in cooperation with the Federal Aviation Administration and Alaska Airlines have been developing a comprehensive wind hazard warning system.

"Our goal is to allow people to fly more and more safely," said Al Yates, project engineer with NCAR.

Turbulence causes the random movement of a plane from side to side and wind shear is the sudden loss of headwind, which causes a plane to drop. Juneau is notorious for both plane-rattling weather conditions because of its mountainous location and its often severe weather.

In the fall, storms move inland from the Gulf of Alaska, bringing Juneau fog and rain. In the winter, northerly Taku winds gust in from the neighboring icefields, Yates said.

Alaska Airlines pilots have special training for flying in Alaska weather, and the company's planes carry special equipment that helps them land at airports such as Juneau's that have been socked in by fog and bad weather, said Bob Barron, NCAR project manager. Before this turbulence-detecting system was developed, pilots' wind data was limited to other pilots' reports and readings of wind conditions at the airport, Barron said.

The development of the wind hazard warning system involves two components. First, measurement devices were installed on Sheep Mountain, Mount Roberts, Peterson Hill, at Eaglecrest and at the airport. Among the devices are instruments called anemometers, which measure wind speed and direction once every second.

Next, an Alaska Airlines jet and a smaller plane owned by King Air have been equipped with sensors and will make descents into Juneau. Scientists will compare the amount of turbulence the planes experience with the measurements taken on the ground, eventually developing an index so pilots can predict wind conditions based on ground wind measurements.

"We are developing a correlation between the ground instruments and the airborne measurements," Barron said. "(The system) will potentially have applications in other locations with strong winds and nearby mountains."

Using planes of different sizes helps the researchers develop wind indexes for commercial and personal aircraft, Yates said.

The project eventually will be taken over by the FAA, Barron said. Pilots currently use the raw data collected by the ground-based measuring devices and Barron and Yates hope the turbulence index will be ready by 2006.

Julia O'Malley can be reached at jomalley@juneauempire.com.