Increasing flights, more observations of clear air turbulence

As more and more flights criss-cross the skies, there are more observations of clear air turbulence, which has increased over the decades very likely due to climate change, and airlines are continuing with efforts to mitigate the impact of turbulence.

Though rare, a Singapore Airlines flight from London to Singapore experienced severe turbulence on May 20 that caused the death of a passenger and left more than 70 people injured. While investigation is still on, the incident has also brought the focus on turbulence, especially the factors of climate change and Clear Air Turbulence (CAT).

In recent weeks, there have also been other incidents of turbulence.

Generally, CAT is defined as any turbulence where there is no cloudiness, and is invisible, which also makes detection difficult by pilots and radars in an aircraft.

"While variations in climate can cause variations in CAT, a robust increase in CAT over decades is very likely to be because of climate change," Manoj Joshi, a Professor of Climate Dynamics at the University of East Anglia, UK, said.

According to him, there has been a real increase in CAT and not just more observations of CAT.

"A big reason why there are more observations of CAT now is that there are a lot more flights now compared to 40 years ago," he told PTI.

Airlines are working on ways to reduce the impact of in-flight turbulence.

When asked whether Air India Express is planning to relook at its existing process during in-flight turbulence, an airline spokesperson said that a spate of incidents across the world do indicate significantly higher levels of flight turbulence caused by extreme weather not experienced earlier.

Against this backdrop, the spokesperson told PTI that the airline has educated its crew to emphasise that guests should keep the seat belt comfortably fastened even if the seat belt sign is not illuminated.

The airline has put laid down procedures wherein in-flight services are suspended based on inputs from cockpit crew regarding anticipated turbulence levels, the spokesperson added.

Responding to queries related to turbulence, an IndiGo spokesperson told PTI that to ensure a secure and comfortable in-flight experience, the airline is constantly exploring new technologies and evaluating in-flight safety announcements.

"Recently, IndiGo ran some trials on a new software and is hopeful of launching another trial for its Airbus fleet in the next 2-3 weeks. Since the agreement is under process, the airline will announce the software name, as per the developments in the trial agreement," the spokesperson said.

Apart from making standard announcements regarding cabin preparation and general safety demonstrations, the spokesperson said IndiGo places particular emphasis on seat belt-related advisories. "Passengers are reminded of the critical importance of keeping their seat belts fastened throughout the flight, especially during turbulence".

For specific situations such as turbulence or inclement weather, the airline has developed situational announcements to prepare passengers and crew for any challenges that may arise.
"These include mist in the cabin, prohibition of mobile use during strong weather conditions, delay in take off (uncontrollable delays-weather conditions), interrupted service (including hot beverages) and operational diversions," the spokesperson said.

Queries related to turbulence sent to Air India, Vistara, Akasa Air and SpiceJet did not elicit responses.

To a question on any perspectives or analysis related to CAT in the Indian subcontinent or Asia, Joshi said tropics can have very turbulent weather systems and weather radars can see such systems, but what climate change might do to CAT near such systems is uncertain.

"One of the most useful sources of CAT information in certain locations are pilots' reports. Combining observations, forecasts, and theory is the key to making the best forecasts of CAT," he noted.
Global airlines' grouping IATA has the 'Turbulence Aware' programme that aims to help airlines mitigate the impact of turbulence.

The platform pools anonymised turbulence data from thousands of flights operated by participating airlines. The real-time, accurate information enables pilots and dispatchers to choose optimal flight paths, avoiding turbulence and flying at optimum levels to maximise fuel efficiency and thereby reduce carbon emissions, as per the grouping.

According to a research paper co-authored by Joshi and published in 2017, there have been strong increases in CAT over the entire globe and in particular the mid-altitudes, which is where the busiest flight routes are.

"We also find that the strongest turbulence will increase the most, highlighting the importance of improving turbulence forecasts and flight planning to limit discomfort and injuries to passengers and crew," it said.

The paper had also said that many of the aircraft that will be flying in the second half of the present century are currently in the design phase and it would therefore seem sensible for the airframe manufacturers to prepare for a more turbulent atmosphere, even at this early stage.