Career Pilot: Rough Ride

In light airplane flying, your first experience with wake turbulence is often running into your own wake when practicing steep turns. It gets your attention, but when the wake is from an airplane of similar size or smaller it’s usually easy to keep things under control. If the wake is generated by an airplane 15,000 pounds heavier than your typical Cessna or Piper trainer—say, a corporate jet—the effects can be substantial and disorienting. Getting tangled in the wake of a large airliner can be damaging or disastrous. Visualizing wake turbulence and knowing its behavior are key to avoidance.

A byproduct of a wing’s lift is a horizontal vortex (think horizontal tornado) that spills off the end of each wing. Each vortex rolls upward and inward toward the fuselage, so the vortex off the right wing rotates counter-clockwise (when viewed from behind) and the left vortex rotates clockwise. If caught in the wake of a preceding airplane, you can distinguish it from regular turbulence because of the rolling motion created by the vortex. Cross the wake perpendicularly, and you’ll get two attention-getting jolts as you cross. Keep that seat belt tight because there’s a good chance you’ll hit your head on the ceiling.

In general, though, you’re most likely to encounter wake when departing from or arriving at a larger airport. There are plenty of avoidance strategies for pilots to take when departing. The most conservative approach is to wait. Typically, a two-minute wait is sufficient. Take note where the preceding airplane first leaves the ground. Wake doesn’t start until the wing starts generating significant lift at rotation. If a preceding jet used 3,500 feet of runway to take off, you can bet you’re safe to take off in your trainer that uses only 1,000 feet to be airborne. Remember, though, that jets and turboprops climb much better than most light airplanes, so be sure you can remain above the wake, or turn upwind of the jet’s flight path.

Large airplanes create the strongest wake when they are heavy, clean, and slow—in other words, a heavy airliner just after takeoff to a faraway destination. The wake produced is substantial and is so hazardous to light airplanes that regulations dictate a mandatory takeoff delay to let it dissipate. As mentioned previously, if you can rotate far before the preceding airplane’s rotation point or get turned away from the wake, feel free to waive the wake-turbulence delay. At large airports light airplanes may be assigned an intersection takeoff one mile down the runway, so be sure that you aren’t rotating right at the liftoff point of a preceding large airplane.

On approach, when following a large airplane such as an airliner, you (or the tower) should space yourself as much as six miles behind the preceding airplane. In the absence of a tower controller, you can easily space yourself using your eyeballs or a traffic device. In general, the trick is to be above and upwind of the larger airplane’s path. Wake settles and gets blown with the wind, so being above and upwind is further avoidance insurance. The stronger the winds, the faster the wake vortices move away and are broken up.

Assume that a large airplane is following a standard 3-degree glideslope. If the runway you’re approaching has an ILS, you can fly it slightly high on the glideslope and slightly upwind on the localizer. Notice where the preceding airplane touches down. Typically, large airplanes touch down at or after the fixed distance markers located 1,000 feet down the runway. Wherever the airplane touches down, you’ll see the puff of smoke from the tires. Plan to land well beyond that spot.

These techniques are all well and good in visual conditions, but in instrument conditions you’ll have to rely on ATC separation and the assumption that the preceding airplane followed a typical path on the localizer and glideslope. Regardless, with proper respect for wake—as well as visualization and knowledge of its behavior—you’ll likely avoid significant encounters.