The video from flugsnug shows an Airbus A321 in flight, as sirens sound in the background. The plane appears to be experiencing some difficulty, wobbling as it attempts to land. It gets very close to the runway at what the caption says is Birmingham Airport, but is buoyed up again by winds, and makes a second try. This time, the plane makes it onto the runway as it is shaken by turbulence.
Turbulence, in fluid dynamics, is a flow that is disrupted by changes in pressure and flow velocity. In plain airplane speak, it’s the violent or unsteady movements that can be caused a number of factors. Turbulence is the most common reason for injury to air passengers, as this can cause panic among passengers or force pilots to make emergency landings. In the United States, there is an estimated 58 injuries annually due to turbulence on airplanes.
Different aspects of the weather can cause different types of air turbulence. Air flows in a horizontal river called a jet stream, which can be thousands of miles long but only a few miles deep and wide. Flight planners generally work with these jet streams to cut fuel costs. But like how a fast-flowing river runs into a solid riverbank, a jet stream can mix with slower moving air, which causes turbulence. This is CAT or clean air turbulence, and is the most common type of air disturbance.
Flight crews all over the world classify turbulence into three: light, moderate and severe. For pilots, light turbulence is similar to a slightly bumpy road for a driver and may only lead the aircraft out of bounds by a few feet. Of course, some passengers may get upset by even the lightest turbulence. Moderate turbulence usually lasts for no more than 15 minutes, but can extend up to several hours. It is, however, common to pilots and this may cause drinks to spill, and unsettle regular passengers. Severe turbulence is very rare, and while extremely uncomfortable for all involved, is not dangerous. The aircraft may deviate in altitude for 100 feet or so, but not thousands of feet as most people think.