We all may have heard the sentence " we may / will experience turbulence on today's flight, so please tighten your seatbelts " on a flight journey or in some airplane movies. And when we pass through turbulence , we will feel the aircraft shaking and vibrating , sometimes it intensifies violently . This is known as turbulence . But what exactly is turbulence ? It is caused mainly due to eddie currents and vertical currents. Both of these phenomenas causes irregular flow of fluid, in aircraft and airspace it is air. This irregular flow of fluid causes the aeroplane to lose its stable motion . Turbulence is often seen associated with thunderstorms , heavy rains and high humidity atmospheric conditions . Turbulence is classified according to its intensity. Light, moderate ,severe and extreme. Severe and extreme turbulences are a headache to the pilots as it may even throw the aircraft out of control and may damage the structure leading to an air accident . Irregular terrains along with wind causes eddie current , the intensity of wind and irregularity determines the level of turbulence . Variation in temparature during heavy summer days also causes turbulence .