More bumps ahead?
Every frequent flyer experiences turbulence at one time or another. While minor turbulence may only cause a slight jolt, severe turbulence can be far more alarming. Essentially caused by variations in air pressure, turbulence creates swirls and eddies in the air around an aircraft and is an inherent part of flying.[1] Pilots and crew undergo extensive training to manage these situations, and modern aircraft are designed to endure such stresses.
From an insurance and risk management perspective, the phenomenon is well understood, its impact well within safety tolerances and the claims that follow incidents of turbulence tend to be relatively minor.
The recent news that someone died from a heart attack, potentially triggered by the stress of experiencing severe turbulence that put more than 20 passengers and crew into intensive care has put the phenomena back into the spotlight.[2] This was followed a few days later by a second notable incident that injured six passengers and six crew.[3]
This article will discuss the causes of turbulence, the reasons why it appears to be becoming more common and what it means for airline insurance renewals. It will also focus on clear air turbulence (CAT), a specific type of turbulence, and look at some of the technologies that are being developed to help aircraft anticipate and avoid it.
It is important to clarify at this point that the causes of the turbulence that created the two recent incidents have not been confirmed beyond that what the flights encountered was “sudden and extreme”. In the case of the incident with the fatality, according to preliminary reports by Transport Safety Investigation Bureau (TSIB) and US representatives from the National Transportation Safety Board (NTSB), the aircraft entered an area of developing convective activity,[4] which creates a very unstable environment for flight.
Turbulence is caused in several ways and defined differently by various organisations,[5] but there are three main causes that concern the aviation industry: mechanical turbulence, convective turbulence and CAT.
Mechanical
Turbulence can be caused by obstructions in the airflow from natural features such as mountains, and the increasing size of some human structures can have a similar impact. This mechanical turbulence is generally well understood and has minimal impact from an aviation perspective because it only tends to occur at low altitudes (below 10,000ft/3,000m ) and is relatively localized around the source of the disturbance. As such, pilots can often anticipate and navigate around areas of mechanical turbulence, making it easier to manage compared to other types.
Convective
Convective turbulence is caused by vertical currents of air which rise and fall as ground temperatures fluctuate. At lower altitudes (below 10,000ft/3,000m), the uneven heating of the ground creates thermal currents that can result in bumpy conditions. This type of turbulence is common on sunny days when the ground heats up rapidly. At higher altitudes (above 20,000ft/6,000m), turbulence can occur when jet streams (fast-flowing air currents in the atmosphere, typically near cruising altitude) interact or change course. These interactions can create severe turbulence, but meteorologists track jet streams and communicate changes with aircraft to minimise the potential disruption. In and around areas of deep tropical convection, such as those found near thunderstorms of tropical cyclones, convectively-induced turbulence can occur. These areas are characterized by strong updrafts and downdrafts, which can create severe turbulence. The potential for convective turbulence in these areas is well understood. Pilots know how to recognise the signs and react accordingly.
CAT
CAT is turbulence that occurs in clear skies, typically at high altitudes, and is not associated with visible weather phenomena such as storms or clouds. CAT is particularly challenging because it can occur without warning and is not easily detectable with conventional onboard weather radar. Research, such as that conducted by the US National Science Foundation National Center for Atmospheric Research (NCAR), suggests that distant storms can contribute to CAT by generating atmospheric waves that can travel far from the storm’s location.[6]
All pilots are taught to read weather conditions in the immediate vicinity of their aircraft, and they have access to detailed meteorological weather forecasts. While weather models provide extensive information on a large scale, they may not capture smaller-scale phenomena experienced by individual aircraft. Although many kinds of turbulence can be anticipated through models and real-time weather updates, there is not yet a completely reliable method for detecting CAT in advance, because CAT occurs without visual cues and cannot be detected by conventional radar.
Pilots report it when they encounter it, but locations can be misreported when travelling at more than 500 miles per hour and consequently be tens of miles out, and equally long-haul flights may not be closely following other aircraft. As a result, CAT can surprise pilots and crews and cause significant turbulence for an aircraft, and that in turn can cause injuries.
Light Detection And Ranging (LiDAR) technologies are helping reduce the challenge of CAT. [7] The approach works by emitting two laser beams from an aircraft, which then receive information about how light is being scattered by small dust and other particulates suspended in the air. LiDAR systems can then use the wavelength variations to spot the transitions in airflow that cause turbulence, helping aircraft move around them.
NASA is also working on ways to spot CAT[8] due to its interest in understanding how flying vehicles perform in a range of different atmospheres. It is developing a network of ground-based microphones that pick up ultra-low frequency soundwaves produced by the phenomena. While creating a global network of the microphones could prove a challenge, they are said to work over a 300-mile radius which should speed any implementation.
NCAR has similarly been developing systems to offer more precise turbulence tools. Algorithms currently installed on over 1,000 airliners are monitoring numerous data points which, when used in conjunction with national weather forecasts and models, will enhance weather prediction models.[9]
The emerging tools are useful, but they are not perfect, and CAT, and turbulence more widely, will remain a challenge for the aviation industry for the foreseeable future.
There is increasing evidence that the warming climate is causing more turbulence for aircraft and that these tools are going to find themselves in more and more demand.
Climate change from carbon emissions is heating up the atmosphere and changing wind speeds, according to scientists including Professor Paul Williams at Reading University. [10] In his analysis, increased turbulence is due to greater differences in wind speed in the jet stream, roughly 26,000 to 37,000ft (8000m to 11,200m) up, which is being driven by differences in temperature between the world’s equator and its poles. When these winds change height, the combination is known as wind shear and is one of the ingredients that creates storms over the oceans.
According to Williams’ research, severe CAT in the North Atlantic has increased by 55% since 1979[11], which is likely to mean that there will be a great deal of emphasis put on developing efficient CAT forecasting tools over the next few years.
It is not only CAT that could increase if the climate is warming. A recent study by the University of Chicago and NCAR suggested that fast jet stream winds could increase speed by 2% for every degree Celsius (1.8° Fahrenheit) that the world warms. According to their research, this means that by the middle of the century the fastest winds could become 2.5 times faster than the average wind because of climate change.[12]
Increased frequency or severity of turbulence could influence route selection, potentially creating a downstream cost to airlines from a fuel consumption perspective, although cleaner aviation fuels and better early-warning systems would all help mitigate some of the effects.
Despite the obvious concern that turbulence causes passengers, the ramifications from an aviation insurance perspective at this stage are limited. While the incidents in May 2024 were a reminder that injuries and even fatalities happen, the Federal Aviation Authority in the US reports that only 34 passengers and 129 crew were seriously injured by turbulence between 2009 and 2022.[13] That said, if incidents of turbulence do increase over the next few years, then the number of claims is also likely to rise.
Serious incidents are still relatively unusual, however. Modern aircraft are built to withstand significant turbulence, technology is improving, and pilots and crew are trained to avoid turbulence where possible and react efficiently when their aircraft hits turbulence. Ultimately, it is a challenge, but it is quantified and many aspects of it are well understood. The best advice is to keep your seatbelt on for as much of your flight as much as you can.
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