Explained: Why do aircraft run into turbulence; how can you be safe during one?

A flight from Mumbai to Kolkata encountered "severe turbulence" on Monday, injuring eight passengers. What happens when aircraft encounter turbulence and what should passengers do?

Eight passengers on board a Vistara flight from Mumbai to Kolkata on Monday, June 7, suffered injuries after the Boeing 737-800 encountered severe turbulence during its descent.

While five of the eight passengers suffered only minor injuries, the other three had to be taken to hospital upon landing.

The civil aviation regulator, Directorate General of Civil Aviation (DGCA), has classified the event as an “incident”, which means that it will investigate the causes behind its occurrence.

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What happened and when?

The Boeing 737-800 aircraft with 113 passengers on board was on its way from Mumbai to Kolkata on Monday, June 7. Around 15 minutes prior to landing, when the aircraft was at an altitude between 15,000 feet and 20,000 feet, it encountered what has been reported as “severe turbulence”.

Upon landing, the passengers were examined by the airport medical team, which cleared all but eight passengers. Five of these passengers were administered first aid, and the remaining three were admitted to three different hospitals in Kolkata.

One of the passengers, a woman aged 61 years, has a fracture in her right hand; another passenger, aged 77 years, has suffered a spinal tenderness injury.

The third passenger, aged 36 years, received a minor cut on the forehead, and was released after being administered first aid.

What happens when an aircraft encounters turbulence?

As a bare concept, turbulence means disruption of airflow over the wings of an airplane, which causes it to enter an irregular vertical motion.

There are at least seven different kinds of turbulence which an aircraft can face.

Turbulence can be weather-related, in which the plane flies through a thunderstorm or a heavy cloud, or it can be clear air turbulence, which is mainly caused by wind or jet streams.

Other kinds of turbulence include “wake turbulence”, which forms behind an aircraft when it flies through air, creating wingtip vortices.

Are turbulence incidents dangerous?

It depends on the nature and intensity of the turbulence. Aircraft face some form of turbulence on a regular basis, and pilots are trained to deal with these disturbances.

However, there have been several instances of turbulence bringing down modern jetliners. But in these cases, while intense turbulence has been the main cause of an accident, several other contributory factors — such as lack of proper training, poor dissemination of weather- or wind-related information — have played a huge role in the accident.

What will the investigation into the Vistara incident focus on?

As a standard practice, the investigation will try to ascertain why the incident caused severe injuries to the passengers. It will look at factors including weather conditions when the plane encountered turbulence, whether the pilots were caught unprepared, and whether they had asked the cabin to prepare for the upcoming disturbance.

Notably, the passenger charter of rights issued by the Ministry of Civil Aviation in 2019 says that in case of death or bodily injury to a passenger on board a domestic flight, the airline is liable to pay compensation up to Rs 20 lakh.

What must passengers do when an aircraft encounters turbulence?

According to the US Federal Aviation Administration (FAA), “passengers can easily prevent injuries from unexpected turbulence by keeping their seat belt buckled at all times”.

The FAA advises passengers to listen to instructions given by the flight attendants; pay attention to the safety briefing at the beginning of the flight and read the safety briefing card; wear a seat belt at all times; use an approved child safety seat or device if a child is under two; and to adhere to your airline’s carry-on restrictions.

This same advice is often given by pilots and flight attendants on Indian domestic flights. Passengers are routinely instructed to go back to their seats and refrain from using the washroom whenever there is turbulence, and the pilot has switched on the seat belt sign.

How can airlines avoid turbulence?

The 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 despatcher; reinforce the carrier’s turbulence avoidance policy through despatcher training; consider re-routing using automation, atmospheric modelling, and data displays; and use all applicable weather data as well as reporting and forecasting graphics.

It also suggests using operating procedures and training to prevent turbulence injuries, emphasise the importance of flight attendants’ personal safety, promote communication and coordination, and gather data and review the carrier’s history of turbulence encounters and injuries.

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