Sunday, March 25, 2007
Wind Shear... Wind Shear... Wind Shear...
Andrew Freedman @ 11:35 AM
Weather is a sensory experience. Atmospheric phenomena need to be felt to be truly understood and appreciated. That's why Dan Rather, who jumpstarted his career in 1961 by reporting live from Galveston, Texas, in the midst of Hurricane Carla, probably knows hurricanes better than any hurricane researcher alive. Tornado chasers also understand the need to experience weather, many of them seem to be addicted to it. So does anyone who has danced outside in a downpour, or ventured out in the middle of a raging blizzard.
Dan Stillman's Forecast
Today: After some morning fog, high pressure will give us a mostly sunny day with highs in the mid 60s.Tonight: Increasing clouds this evening, then turning mostly cloudy overnight. Lows in the mid 40s.
Tomorrow: Mostly cloudy with a slight chance of a late-day sprinkle or shower, highs 55-60.
A detailed week ahead forecast will appear tomorrow.
A recent flight into St. Thomas for a family vacation allowed me to experience low-level wind shear, an occurrence I've read about but had fortunately avoided. I'm all for experiential learning, but this made me freak out nearly to the degree of Richard Simmons reacting to a flaming cooking aid.
The American Meteorological Society defines wind shear as "The local variation of the wind vector or any of its components in a given direction." In other words, wind shear is wind that changes direction and/or speed between two points in the atmosphere. The shear can be vertical or horizontal.
According to wikipedia (http://en.wikipedia.org/wiki/Wind_shear), pilots refer to wind shear as "a change in airspeed of 15 knots per thousand feet, and/or a change in heading of 30 degrees or greater per thousand feet."
I'd add another definition. Wind shear (noun): pee-in-your-pants scary.
I've read about and watched documentaries of the disastrous effects of wind shear on aircraft, such as the crash of Delta flight 191 in Dallas in 1985 that killed 135 people. As a result of this accident and others, commercial aircraft are currently outfitted with wind shear alert systems that warn pilots of dangerous conditions with a businesslike voice that chimes in with the discomforting chant of "wind shear... wind shear... wind shear."
My March 14 Delta flight from Atlanta was routine until the last two minutes of the approach into the hilly Caribbean island. Having been warned by the captain of possible turbulence due to windy conditions, I didn't think much of the first rush of air that knocked our Boeing 757 slightly off course as we maneuvered over the ocean to the west of the airport.
The second distinct bump featured a stomach-churning drop, forcing me to look down at the ocean to gauge how far we'd have to fall before I'd either be swimming or dead.
Then a break. Smooth air. A little more power. More flaps. Some yaw (side-to-side motion) as the pilot-in-command worked the rudder to stay aligned with the relatively short runway. Followed shortly thereafter by another drop.
Then another.
Then another.
Gasps from the passengers. Sweat and adrenaline from me.
It was at this point that the young couple sitting to my right locked arms and I realized I might die alone, as my relatives had already flown in from elsewhere on a separate flight. The woman, gangly but wholesome, peered over my shoulder as her short stocky boyfriend stared resolutely ahead, as if not looking would stop the plane from plummeting.
We continued inbound, dipping well below the level of the hills that encroach on the airport from the north. The air felt angry.
We reached 500 feet and continued to descend. Another drop. More gasps. Individual waves were visible in the ocean. My arms began to move forward instinctively as I half-contorted into the crash position. But it was a half-hearted crash position resulting from embarrassment and disbelief, like the run that I often break into whenever I trip and almost fall on a crowded sidewalk.
We went lower still. We rocked from side to side. More rudder action. Another drop. Then the nose tilted up, and the engines spooled up into a roar. We achieved a positive rate of climb and screamed over the airport in a right bank at full power. "He's rejecting the approach and is going around," I said to no one in particular.
"Ladies and gentleman from the flight deck, an update on what just happened, we were getting some indications of wind shear on approach. We're going to go around and try it again and hope it's a little less windy now. We just need to make sure it's safe."
The second approach went much better, although we caught a powerful gust just as we crossed over the runway threshold and the pilot had to wrestle the big Boeing to the ground. The passengers clapped. The couple next to me released their embrace and laughed. I laughed with them, covered in sweat.
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