News Weather
This Tuesday, May 21, a Singapore Airlines Boeing 777-300ER, traveling from London to Singapore, experienced violent turbulence over Burma, causing one victim and several injuries. How can we explain such turbulence at this altitude?
A fall of 600 meters per minute
The plane was cruising at approximately 11,300 meters altitude, where the temperature is close to -40°C. He was supposed to reach Singapore, further south, but had to be diverted to Bangkok airport, in particular to take care of the injured. Around 3 hours from arrival, the plane passed through an area of extreme turbulence. Most of the passengers, who had unfastened their seat belts, were surprised by a sudden rise then a sudden fall of the aircraft due to a “Air gap”, causing the plane to go from 11,300 m to 9,400 m in 1 to 3 minutes, i.e. a fall of 1,900 m, losing 600 m per minute. This extreme vertical movement literally propelled the passengers to the ceiling of the aircraft.
Airplane turbulence: several possible meteorological causes
Turbulence is one of the greatest dangers facing aviation. Several meteorological configurations are conducive to this turbulence, notably frontal zones where warm air meets cold air, jet streams, and convergence zones.
In this case, the plane was crossing a very unstable area linked to the intertropical convergence above Burma, at the start of the rainy season. Within this zone, storm clouds, cumulonimbus clouds, generate powerful vertical currents (ascending and descending), which planes avoid at best by going around them. But in certain circumstances, the plane passes through the storm, risking being confronted with these currents. The “air hole” therefore designates, in reality, the sudden temporary fall of the plane which plunges with the current. It loses lift, falling flat after being briefly sucked upward. This situation is different from the “stall” of an airplane, which occurs when it nosedives or falls to one side. An investigation will determine the precise circumstances of the accident.
There are other weather parameters that can cause turbulence and air pockets.
– Air holes in “clear air”. This situation resembles that encountered by the Boeing. Even in the absence of a storm, differences in temperature and air density can cause the plane to suddenly descend briefly, flat, and vibrate sometimes quite spectacularly.
– Jet streams, or “jet-stream”. These high altitude winds (8000 to 10000 m) do not circulate above the intertropical zone, but mainly at temperate latitudes. These very fast winds (150 to 200 km/h) are generally favorable to aviation, by “carrying” aircraft, but there are certain situations where the aircraft will encounter a rapid change in speed and direction. which can cause recognizable shaking and vibrations. These sudden changes in wind direction are called “shear”.
– Fronts or frontal disturbances. These are the usual disturbances caused by the movement of air masses. When a plane crosses a front, it is confronted with changes in wind direction and instability, particularly if it is a cold front, when cold air encountering hot air. Ascending and descending currents within the clouds can shake the plane, which is common, even in domestic flights in our country.
Turbulence therefore has multiple meteorological causes. Although they are mostly well controlled by pilots, causing only a few shocks for passengers, certain weather patterns can be significantly stronger, causing incidents of this type. Thunderstorms are the primary cause, particularly over the Intertropical Convergence Zone, which is the most dangerous area for aircraft on the planet.
HAS