What causes the turbulence encountered by planes? What means do pilots have to avoid them? On Tuesday, a Singapore Airlines flight from London to Singapore had to make an emergency landing in Bangkok (Thailand) after experiencing, according to the company, “extreme and sudden turbulence”. The toll is particularly heavy: one dead and 71 injured, around twenty of whom are still in intensive care.
20 minutes asked Bertrand Vilmer, a former experimental test pilot and aeronautical engineer associated with the Icare cabinet to enlighten us on this rare event.
What causes turbulence?
Turbulence is everywhere and all the time. There are even some that we pass through without feeling them. This is the meeting of moving air masses which have opposite directions, an east/west air movement which, for example, meets another west/east one. Whenever there are significant differences in temperature or water concentration in the atmosphere, turbulence can occur.
There are two types of turbulence. When everything is clear, or near cirrus clouds which are clouds which indicate strong winds, we speak of “clear sky” turbulence. The other category of turbulence occurs most frequently in cumulus clouds, vertically developing convective clouds.
Are pilots necessarily aware of the presence of turbulence on their route?
Pilots have weather maps that they consult before flying, information during the flight and they have a weather radar. Among the forecast elements there is the symbol CAT – for Clear air turbulence – on the maps. Storm clouds are also shown there and they will also see them on radar. Usually there are warning signs, small turbulences during which they begin to reduce the speed of the aircraft. Then, after asking passengers and then crew personnel to strap in, they are required to attempt to navigate around storm cells or turbulence in “clear skies”.
So we can think that this could not have been possible for the London-Singapore flight?
We don’t yet know what exactly happened. What the testimonies say is that the plane was flying at approximately 12,000 meters and that it suddenly nosedived, descending 1,800 meters. This is currently interpreted as turbulence. There are indeed some that are very difficult to avoid even if such violence is still very rare.
+ information on the London-Singapore flight
But this descent can also be due to another problem, a failure of the flight controls or the autopilot. There are black boxes on this plane, we must let the commission of inquiry do its work.