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to avoid encountering that airplane’s wake. If you are IFR in instrument meteorological conditions controllers will provide separation from airplanes and the expected location of their wake turbulence. But even if you’re IFR in VMC, or ATC advises you of traffic and you report it the traffic sight, you assume responsibility for avoiding the airplane and its wake turbulence, too.
Most instruction and guidance about wake turbulence avoidance focuses on avoiding wakes during takeoff and landing. Certainly, that’s where you’re most likely to have a wake turbulence encounter, because you are sharing a very small airspace with other airplanes (and the air they disturb). Comparatively little time is spent on training teaching and reviewing how to avoid wake turbulence encounters away from the runway. Yet as I said earlier, it’s our responsibility to avoid wake turbulence anywhere it may exist in visual conditions.
Uncontrolled Roll
A Canadair Challenger 604 was cruising at FL340 over the Gulf of Oman in January 2017. An Emirates Airways Airbus A380, en route from Dubai to Sydney, Australia, passed overhead at FL350, 1,000 feet higher than the business jet. The crew of the Challenger was quoted by FlightServicesBureau.org as saying: “A short time later (one to two minutes) the aircraft encountered wake turbulence sending the aircraft into an uncontrolled roll, turning the aircraft around at least three times (possibly even
The wake behind an aircraft consists of two counter-rotating cylindrical vortices. The strength of the vortex is governed by the weight, speed, wing shape and wingspan of the generating aircraft.
five times). Both engines flamed out [and] the aircraft lost about 10,000 feet [before the crew] was able to recover the aircraft, restart the engines and divert to Muscat.
The aircraft received damage beyond repair due to the G-forces [encountered], and was written off.”
Anyone who has ever flown a 360-degree, level steep turn and hit a bump at the end knows even airplanes as small as a Cessna 150 leave a wake of disturbed air behind them. When the airplane trailing a wake is bigger than the one you’re flying, its wake turbulence may be strong enough to upset your airplane – or worse.
So how do wake vortices behave? What strategies can we use to avoid them, in climb, cruise and descent as well as during takeoff and landing?
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December 2017
TWIN & TURBINE • 13
PAUL BOWEN PHOTO