Flight Training - February 2013 - 41

FLIGHT LESSON

By Jeremy Elson
FLIGHT LESSON offers the opportunity for pilots to learn from the experiences of others.

OVERCOME BY WAKE TURBULENCE

SPINNING IN A TUNNEL

e’re having a poker game, you should come up!” my friend Taylor had said. I knew I’d be the sucker at the table but agreed. This is how, one fine fall weekend, I found myself flying my Cessna Cardinal from Los Angeles up to Northern California.
True to its name, Silicon Valley is a long, narrow basin just a few miles wide, sandwiched between two parallel mountain ranges. Aircraft arriving from the south typically fly straight up it. On that day, I was no exception, flying at 4,500 feet, northwestbound as I made my way to the small Palo Alto Airport. The air was clear and calm—one of those days that makes flying feel so easy and carefree. I was getting VFR flight following from NorCal Approach. “Cardinal Nine-Seven Hotel, traffic at your six o’clock will be passing 500 feet above you, a 737 restricted to 5,000,” the controller told me. “Caution, wake turbulence,” she added perfunctorily. Wake turbulence is a disturbance in the air that is generated by any wing that’s flying. Wings go up by forcing air down. This generates swirling vortices at each wing tip that slowly sink to the ground, a little bit like the wake that spreads behind a speedboat planing through water. Unlike a boat wake, wing-tip vortices are usually as invisible as the air they’re in. The heavier the airplane, and the slower it’s going, the more air must be sent Earthward to keep the airplane aloft—and the larger these invisible menaces become. Controllers use the standard phraseology, “Caution, wake turbulence,” to warn pilots of smaller aircraft that their paths might cross the wake of a larger one. On that sunny afternoon, I got the warning, but didn’t pay attention: I’d heard it so many times in the year I’d had my certificate that it had virtually lost its meaning. I leaned forward and looked up to see an awesome sight: a big commercial jet painted in Southwest Airlines' livery passing right over my head! It was fantastic getting a close-up view of such a big machine in motion. It was flying the same track I was, right up the center of the valley on the approach into San Jose. I got a nice long look as he lazily pulled ahead of me. I had a big, dumb grin on my face, thinking, this is one of those cool sights that only pilots get to see.

My reverie was abruptly interrupted by the realization that my airplane was in a 20-degree bank to the left. I turned the yoke to the right to correct it. Then something shocking and terrifying happened: absolutely nothing. Not having control of your airplane is truly frightening. All the fancy-pants aeronautical decision making in the world isn’t worth much if the airplane just won’t do what you tell it to do! I turned the yoke farther and farther to the right, but the airplane continued rolling left. The yoke reached its limit but the airplane was still banked 30 degrees. We were in a standoff: With full aileron deflection, the airplane was not rolling any farther left, nor was it rolling back wings-level. It seemed quite indifferent to my control input, stubbornly flying with the right wing up as if it were stuck. I realized I must be inside a huge, swirling wake vortex from the jet that had just passed overhead. The jet had passed only 500 feet above me so the vortex hadn’t had much time to disperse. It was strong because the jet, close to landing, was slow. And since it was flying parallel to me, I was flying straight down the long axis of the vortex like I was in a spinning tunnel. The controls abruptly returned to normal as my airplane exited the vortex. The airplane rolled right quite enthusiastically, putting me wings-level in an instant. I straightened the yoke and the airplane kept on flying as if nothing had happened. It felt like forever, but the whole encounter lasted perhaps two or three seconds. I’m lucky I was able to react so quickly. If I’d been fussing with a chart or searching my flight bag, the encounter would have gone differently. The airplane might even have gone inverted. During my pilot training, the only wake-avoidance procedures I learned were those used at airports: take off earlier and land later on the runway than a large airplane that has just taken off or landed. On that day, I learned a new lesson: When I hear “Caution, wake turbulence,” I keep my hands on the yoke!

SARAH HANSON

FEBRUARY 2013 FLIGHT TRAINING

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Flight Training - February 2013

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