Two planes operated by German airlines recently got caught up in severe turbulence. But was it dangerous, and what was the cause?

Turbulence is a sudden change in airflow, and can be caused by several different factors, such as wind or temperature gradients.

Whilst uncomfortable and an inconvenience, turbulence is rarely dangerous, and is a good sign that the plane is performing well to counteract external forces. Often, what feels like large, dramatic drops during turbulence, are just a couple of metres.

In the recent cases, one of the Lufthansa planes was reported to have dropped around 300 metres and did cause minor injuries to those who weren't wearing their seatbelt at the time.

The significant turbulence was caused by "Clear Air Turbulence". This occurs from time to time in seemingly fine weather, without any visible warning signs such as storm clouds on the horizon.

It is caused when different air masses collide and move at different speeds to one another, often at the altitudes of commercial aircraft at around 10,000 metres. CAT can occur over mountain ranges or in the jet stream, the belt of strong winds in the atmosphere.

Often pilots will utilise the benefits of the jet stream when it is a tailwind, to accelerate the flight time, but remain higher or lower than it in a headwind to avoid turbulence.

So, if you're headed on a plane any time soon, just remember, although unnerving, turbulence is a shift in the airflow and completely normal.

Airplanes are designed to withstand extreme amounts of stress, but if you want to feel the effects of turbulence less, pilots suggest seats directly over the wings of a plane, or towards the front.