Windshear and Microburst — Page 181, Lesson 274

I want to walk you through a critical safety topic: low-altitude windshear and microbursts. Let's start with the definition. Low-altitude windshear is a sudden change of wind velocity along the final approach path, along the runway, or along the take-off and initial climb-out path. In other words, it's a rapid shift in wind speed or direction that happens right where we're flying low to the ground — the most vulnerable phases of flight. We also need to distinguish two types. Vertical windshear is the change of the wind vector with height. Horizontal windshear is the change of the wind vector with horizontal distance. So one is a change as you go up or down, the other is a change as you move forward or sideways. Now, where does this come from? The most potent examples of windshear are associated with thunderstorms — specifically cumulonimbus clouds. But windshear can also happen with other meteorological features. Let me list them: the passage of a front, a marked temperature inversion, a low-level wind maximum, or a turbulent boundary layer. Topography or buildings can make the situation worse, especially when there's already a strong wind blowing. So what does windshear actually do to an aircraft? The effect is an abrupt displacement from the flight path, and it requires substantial control action to counter it. A windshear encounter is a highly dynamic event — it can be extremely uncomfortable, it can strike suddenly, and it can have devastating effects. An encounter may cause alarm, a damaged landing gear, or even a total catastrophe. That's why the most vital defence is avoidance. But avoidance only works if you recognize it in time. Before a pilot can apply the recovery techniques he's been taught in training, he must be able to recognize that the aircraft is encountering windshear. There's an unavoidable time lag between the pilot first seeing the signs, recognizing them, applying the appropriate recovery techniques, and the aircraft responding accordingly. Reducing that time lag to a minimum means early recognition of the windshear condition by the pilot, and the unhesitating application of the recommended windshear recovery techniques. Recognition and reaction times are largely a function of training — training gives the pilot the ability to spot the signs quickly and act without hesitation.