You are flying into a controlled airport with the intent to land and ATC states, “ Cessna N617WT winds 160 at 5, cleared to land Runway 18, caution Wake Turbulence”. What is ATC trying to tell you with the message “caution wake turbulence” and how do you avoid the hazard associated with it?
First off, to avoid wake turbulence we have to know what it is and how it is created. Simply put, wake turbulence (also known as wing tip vortices) is the product of created lift from the wings. The creation of this wing vortex generation is made by the creation of a pressure differential over the wing surface. As we know from basic lift aerodynamics, the lowest pressure occurs over the upper wing surface and the highest pressure under the wing. Due to that pressure differential, the rollup of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wingtips.
Okay now we know what it is, why is it so dangerous?
Compared to our little Cessna, large aircrafts wake can impose rolling tendencies exceeding the roll-control authority of the encountering aircraft. A lot depends on the encountering aircrafts wingspan. The larger the wingspan the larger the vortices, therefore, greater rolling tendencies are imposed. The greatest vortex strength occurs when the generating aircraft is
More lift is required
Higher AOA is required to counteract lack of airspeed
The extension of flaps and other wing surface devices will change the characteristics of flight vortex (dirty, indicates delayed vortices)
Now that we know what it is and why it’s so dangerous, how do we avoid it?
When landing behind a larger aircraft— stay at or above the larger aircraft’s approach flight path and land beyond its touchdown point.
When departing behind a large aircraft—rotate prior to the rotation point and climb above its climb path until turning clear of the wake.
Next time ATC gives you a caution such as “wake turbulence” you will know what you’re working with and looking out for. Make sure you exercise the proper precautions and avoidance techniques! You never know when you could encounter another large aircraft on takeoff and/or landing. Fly safe!