What causes turbulence and can it cause a plane to crash?”
In fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time. Flow that is not turbulent is called laminar flow. The (dimensionless) Reynolds number characterizes whether flow conditions lead to laminar or turbulent flow; e.g. for pipe flow, a Reynolds number above about 4000 (A Reynolds number between 2100 and 4000 is known as transitional flow) will be turbulent. At very low speeds the flow is laminar, i.e., the flow is smooth (though it may involve vortices on a large scale). As the speed increases, at some point the transition is made to turbulent flow. In turbulent flow, unsteady vortices appear on many scales and interact with each other. Drag due to boundary layer skin friction increases. The structure and location of boundary layer separation often changes, sometimes resulting in a reduction of
Brutal freak turbulence is the most plausible cause of the crash of Air France Flight 447. If lightning alone caused the crash questions would be asked about the design of the A330, a medium-sized long-range airliner that enjoys a high reputation with the world’s airlines. No major crash has been directly blamed on lightning for more than four decades. Large aircraft are regularly struck by lightning but very rarely suffer damage from the bolt, which passes along the exterior of the fuselage and is diffused into the open air, mainly from small tabs on the trailing edge of the wings. Recent US statistics showed that every commercial aircraft is struck by lightning at least once a year. The violent turbulence in the heart of storms is a threat to even large aircraft, however. Airliners usually avoid them by flying over or around the biggest ones. Smaller aircraft are from time-to-time torn to pieces in storms or thrown on the ground by them when they are approaching to land or taking off
Turbulence is caused by sudden changes in air movement that cause the aircraft to pitch, yaw and roll. There are two types of turbulence: so-called “clear air turbulence”, which can happen when different bodies of air meet at high altitudes, such as near mountain ranges or on the fringes of the jet stream in the north Atlantic. Storm turbulence is more easily detectable as it contains moisture that can be picked up by aircraft radar. But if the plane flies into it, it is hit by sudden air movements that result in it being buffeted by upward and downward draughts of air. Turbulence-related crashes happen once a decade, according to aviation consultancy Ascend. Examples include the crash of an Austral airlines McDonnell Douglas in Uruguay with the loss of 69 passengers and five crew in 1997. It is believed that turbulence caused the recent crash of Flight 447.
