A 100-foot tower going up at the Egan Drive pullout in the Mendenhall Wetlands will be the most prominent link in a network to alert pilots of Juneau's wind shear.
"They need a tower to support the system," Allan Heese, Juneau's airport manager, said. Last year, a temporary tower was set up at the same parking area.
The low-level wind shear alert system has two towers previously erected in Juneau, said Joette Storm, Federal Aviation Administration spokeswoman in Anchorage. Both are on the other side of the airport. One is at Crazy Horse Drive, and the other is on Battleship Island near Smuggler's Cove.
"Wind shear has been an issue for incoming jets," Storm said.
Wind shear involves rapidly changing wind currents and is most dangerous when planes are taking off and landing.
A plane encountering a strong head wind followed by a downdraft and tail wind will have reduced airspeed and experience a loss of lift and elevation, according to FAA literature.
The towers in the alert system hold instruments that measure wind speed and direction, sending information to the airport tower so pilots can be warned of dangerous conditions.
Without the alert system, people working in the airport tower would find out about wind shear conditions only after pilots told them about sudden changes they encountered.
During the trial of the system with the temporary towers in place last year, the FAA's air traffic manager at the airport, Steve Turner, said the terrain, with the mountains flanking the channel and an ice field, has an effect on the unique movement of air near Juneau International Airport.
"We know it causes a lot of disturbed air in this area," he said.
The Mendenhall Wetlands have hosted other equipment measuring wind shear. The FAA conducted tests from the fall of 2002 until February 2003. Two instrument-filled aircraft conducted numerous test flights and a mobile Doppler radio parked in the Mendenhall Wetlands took readings.
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