What is wake turbulence?

This question was posed to me through the website this week and by coincidence I encountered a little ‘wake turbulence’ this morning.

Have you ever been sitting peacefully on board as a passenger and suddenly felt an unannounced jolt. Short in duration, but a little like some giant has given the jet an abrupt shake? The chances are that this was a wake turbulence encounter. As ‘picturing air’ can be a rather abstract concept, it may be best to use a more visual example, such as water. As a large ocean liner or small power boat carves its way through the water, you will notice the disturbed surface behind it ” this is the vessel’s wake. Similarly, an aircraft creates a disturbed body of air behind it as it flies. Like the boats, the larger the aircraft, the greater the amount of disturbed air, however the intensity of the wake can be subject to other factors such as the phase of flight.

One of the main components of wake turbulence can be swirling cork-screws of air trailing back from the aeroplane’s wing-tips known as ‘wing tip vortices’. These are most significant as the aircraft takes off or approaches to land, but that is not to say that a cruising airliner at high altitudes does not create a wake ” it certainly does.

In the interests of both safety and comfort, aircraft are assigned a wake turbulence category and separated by a time or distance in the airport terminal area. This minimises the chance of flying into the preceding aeroplane’s wake, particularly during the critical phases of flight ” take-off and landing. Normally the wind will blow the wake away by the time the next aircraft passes through the same parcel of air. However, on those beautifully still days when it is wonderful to fly, wake can loiter and give the following aircraft a jolt as there is no wind driving the wake away.

The same jolt can be felt at altitude occasionally when the wake of another aircraft drifts down towards the earth. Aircraft flying on airways beneath may encounter the higher aeroplane’s wake. Once again, the wind will generally move and dissipate the wake.

Wake turbulence events are not particularly common and air crews and air traffic controllers alike take preventative measures to minimise its occurrence. Still, there are infrequent occasions when an encounter takes place, but it is usually short in duration. Wake turbulence is a natural side effect of our passage through the air. It is the fact that it generally occurs when conditions are ideal that causes wake turbulence to can catch the comfortably relaxed passenger a little off guard.