An Air India aircraft encountered severe mid-flight turbulence on Tuesday while flying from Phuket to Delhi, experiencing a sudden drop of about 300 feet and resulting in injuries to some of the passengers and cabin crew members. Prima facie, the injuries didn’t appear to be too serious, although medical examinations of the injured were underway. According to sources in the know, at least 14 people on board the Airbus A320 aircraft sustained injuries. The incident is being investigated by aviation safety regulator Directorate General of Civil Aviation (DGCA).Turbulence is a routine occurrence with scores of flights encountering it to varying degrees on a daily basis all over the world. Some of it may be near the ground, when strong winds around the airport can cause turbulence as aircraft take off or land, or at higher altitudes, where an updraft or downward flow of air in storm clouds can trigger some turbulence as planes fly through or near them. Turbulence also occurs on the edges of jet streams — strong, fast, and narrow air currents that circle the globe.While turbulence is common, serious injuries caused by it are rare, and fatalities even more so. But there have been exceptions. For instance, one passenger died while several flyers and crew members sustained injuries — including some serious ones — when a Singapore Airlines jet was hit by sudden and severe turbulence over Myanmar in May 2024. There have been other incidents of turbulence causing injuries to those on board as well.With the explosive growth in air traffic over the past few decades, along with the impact of global warming and climate change, the incidence of severe turbulence — particularly the difficult-to-predict clear air turbulence — has grown, studies show. And what is worrying is that it could get worse in the future as climate change intensifies.Modern aircraft are over-engineered to deal with turbulence. Weather forecast and monitoring technology is continuously improving, and so is pilot and cabin crew training. Yet, there may be a need for passengers, airlines, and aviation regulators to exercise some extra caution. Keeping the seatbelt fastened at all times — and not just when the seatbelt sign comes on — is the simplest yet the most effective measure that drastically reduces the possibility of turbulence-related injuries.A guide to turbulenceTurbulence is an irregular motion of the air resulting from circular whirls of air, or eddies, and vertical air currents—updrafts and downdrafts. Its severity can range from a few minor bumps during the flight to the aircraft tossing around with rapid and harsh changes in altitude, which can lead to injuries to those on board and also result in structural damage to the plane in rare cases.As per the United States (US) National Weather Service (NWS), the intensity of turbulence is usually classified as light, moderate, severe, or extreme.Story continues below this adLight turbulence could lead to slight erratic changes in the plane’s altitude and attitude—aircraft orientation with respect to the horizon. In moderate turbulence, there may be more notable change in the aircraft altitude and attitude, but the plane remains well under control. Severe turbulence is marked by significant and sudden changes in the altitude and attitude, and could also lead to the aircraft momentarily going out of control. In the case of extreme turbulence, the plane is “violently tossed about” and is “practically impossible to control”.When it comes to causes of turbulence, the NWS lists four broad categories: Mechanical, thermal or convective, frontal, and wind shear. These causes are behind the various types of turbulence that aircraft experience on a regular basis.Mechanical turbulence is caused when friction between the air and the ground—irregular terrain and man-made obstacles—leads to formation of eddies. This kind of turbulence is usually found at lower altitudes, but in the case of aircraft flying over high mountain ranges, it could happen at relatively higher altitudes as well. When caused by turbulent eddies formed over mountains, it is referred to as ‘mountain waves’.Also Read | One year of AI 171 crash that killed 260 people: What probe report could focus onConvective or thermal turbulence is caused when air pockets are formed as hot air from certain surfaces on the ground rises rapidly while cooler air descends, resulting in convective air currents. These currents are known to cause difficulties during approach as they tend to affect the rate of descent.Story continues below this adWhen the lifting of warm air by the sloping frontal surface and friction between two opposing masses of air produce turbulence, it is called frontal turbulence. This type of turbulence is most palpable when warm air is moist and its intensity increases with thunderstorms. It is most common close to thunderstorms.As per the NWS, wind shear is the “change in wind direction and/or wind speed over a specific horizontal or vertical distance”. Atmospheric conditions where wind shear exists include temperature inversion areas, troughs and lows, and around jet streams. Clear air turbulence (CAT), which can be sudden and severe as it is extremely difficult to forecast or see, may be considered a type of wind shear-related turbulence.The invisible CATTurbulence that occurs outside of clouds and usually above the altitude of 15,000 feet is called clear air turbulence, or CAT. To be sure, it is still not clear what kind of turbulence caused the Singapore Airlines incident. Analysts point to two possible triggers—a few severe thunderstorms in the region, and a distinct possibility of CAT.While most other types of turbulence can be predicted using data from earth sensors, satellites, radars, and even visual cues, cloudless CAT can come like a bolt out of the blue as these technologies and equipment tend to miss it completely. This makes it virtually impossible for the pilots and the airlines to plan ahead for it, making CAT an unpleasant surprise in most cases.Story continues below this adIn the case of turbulence caused due to thunderstorms, the severe turbulence is not just within the clouds, but could extend up to 20 miles, according to the NWS. Pilots usually avoid thunderstorms, but fast-changing thunderstorm activity and the large affected area range could, at times, give them little to no time to steer clear.As per accounts of some of the passengers on board the Singapore Airlines flight, the severe turbulence hit the aircraft suddenly, not giving many the time to even fasten their seatbelts.A meal service was on at the time of the incident and a number of passengers were not strapped in. The sudden and violent fall in vertical rate would have exerted negative G force—essentially an upward push—on the people and objects inside the aircraft. Anyone or anything not secured or strapped in would have been thrown upwards, which is consistent with the head and neck injuries suffered by many passengers when they crashed into the overhead bins. Then when the aircraft would have gained altitude rapidly, the G force would have brought them down crashing on the aircraft floor or the seats.The climate change factorThe worrying aspect is that climate change could make turbulence more frequent and severe, studies suggest.Story continues below this adA study published in 2023 by researchers from the University of Reading in the UK and the UK Metrological Office, found large increases in CAT between 1979 and 2020 around mid-altitudes and aircraft cruising altitudes. Over the North Atlantic, severe-or-greater CAT duration rose over 55 per cent in the four-decade period.Reporting similar increases in turbulence all over the world, the study said the increase is almost certainly the result of climate change, which is strengthening the jet streams that cause turbulence. The researchers also estimated that severe turbulence would increase in frequency more than light or moderate levels of turbulence.“Our study represents the best evidence yet that CAT has increased over the past four decades, consistent with the expected effects of climate change,” the researchers said in the study’s summary.In another study published last year, Seoul National University’s Jung-Hoon Kim and his colleagues inferred that not just CAT, but even mountain wave turbulence and near-cloud turbulence are set to intensify with climate change going ahead.Story continues below this ad“We show that turbulence generated from all three sources is intensified with higher occurrences globally in changed climate compared to the historical period. Although previous studies have reported intensification of clear-air turbulence in changing climate, implying bumpier flights in the future, we show that intensification of mountain-wave turbulence and near-cloud turbulence can also be expected with changing climate,” the authors of the second study said in its abstract.Keeping safeIt needs to be underlined that even when severe turbulence is the main primary trigger for an accident, there could be multiple contributory factors, including poor training of crew and inadequate dissemination of weather or wind related information. Such incidents do serve as reminders of the need to constantly review and improve systems and processes.The US Federal Aviation Administration (FAA) recommends that carriers should improve dispatch procedures by keeping communication channels open full-time, include turbulence in weather briefings, promote real-time information sharing between pilot and dispatcher, reinforce the air carrier’s turbulence avoidance policy through dispatcher training, consider rerouting using automation, atmospheric modelling, and data displays, and use all applicable weather data as well as reporting and forecasting graphics.The FAA, which is the leading aviation regulator globally, also suggests using operating procedures and training to prevent turbulence injuries, emphasise the importance of flight attendant’s personal safety, promote communication and coordination, and gather data and review the air carrier’s history of turbulence encounters and injuries.Story continues below this adFollowing the 2024 incident, Singapore Airlines reviewed and changed some of the cabin crew’s operating procedures. The airline announced that it will suspend meal services whenever the aircraft fly through turbulence. The carrier now also requires its cabin crew to be seated with seatbelts fastened during periods of turbulence. Various airlines, including Air India, stop serving hot beverages when the plane encounters turbulence. In cases where the turbulence is expected to be strong, it is not uncommon for the pilots to even direct the chain crew to suspend meal services and strap into their seats.As a passenger, it is best to keep the seatbelt fastened at all times, unless unavoidable, like when using the lavatory. Most serious injuries are caused when turbulence dislodges the passengers from their seats, and the only way to prevent it is to be strapped in. Announcements advising passengers to keep the seatbelts loosely fastened even when the seatbelt sign is off are not without reason.