TURBULENCE IN SKY

The Regulators and Airlines have a long history of working to prevent turbulence injuries. Guidance material has been developed to help crew avoid turbulent conditions and also methodology to minimise the risks when airplanes do encounter turbulence. Recent incident on 21 May 2024, Singapore Airline flight from London to Singapore encountered severe turbulence over Andaman Sea leading to death of one passenger and severe injuries to 21 and minor injuries to 20 other has once again highlighted the importance of crew and passenger safety. Other such incidents which were prominently reported in media were-

• 01 May 22 , SpiceJet Mumbai – Durgapur flight encountered severe turbulence in descent phase, injuring 14 Passengers and three cabin crew member, 2 passengers were admitted to ICU for severe injuries.
• On 07 Jun 2021, Vistara flight from Mumbai to Kolkata encountered severe turbulence and 02 passengers received severe injuries while other 02 received minor injuries.

If we look at the data from Federal Aviation Administration, it is easy to understand that such weather related injuries have increased over the years. The Table below shows the number of serious injuries in US registered aircrafts.

An “Accident” means “an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person suffers death or serious injury, or in which the aircraft receives substantial damage.”

 A  “fatal injury” means “an injury which is sustained by a person in an accident and which results in his or her death within thirty days of the date of the accident”.

A  “serious injury” means “an injury which is sustained by a person in an accident and which  (1) requires the individual to be hospitalised for more than 48 hours, commencing within seven days from the date the injury was received; (2) results in a fracture of any bone (except simple fractures of fingers, toes, or nose); (3) causes severe hemorrhages, nerve, muscle, or tendon damage; (4) involves any internal organ; or (5) involves second-or third-degree burns, or any burns affecting more than five percent of the body surface; (6) involves verified exposure to infectious substances or injurious radiation.”

While a “Minor injury” means “any injury that is neither fatal nor serious”.

REASONS FOR TURBULENCE

Clear Air Turbulence

Clear Air Turbulence (CAT) is a recognised problem that affects all aircraft operations and it is troublesome because it is often encountered unexpectedly and frequently without visual clues to warn pilots of the hazard. CAT is defined as “sudden severe turbulence occurring in cloudless regions that causes violent buffeting of aircraft.” It is associated with higher altitude (more than 15,000 ft altitude) turbulence associated with wind shear. The most comprehensive definition is high-altitude turbulence encountered outside of convective clouds. This includes turbulence in cirrus clouds, within and in the vicinity of standing lenticular clouds and, in some cases, in clear air in the vicinity of thunderstorms. Generally, though, CAT definitions exclude turbulence caused by thunderstorms, low-altitude temperature inversions, thermals, strong surface winds, or local terrain features.

One of the principal areas where CAT is found is in the vicinity of the jet streams. Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. In jet streams, winds blow from west to east, but the flow often meanders southward and northward in waves. CAT is more likely to be found on the poleward side of the jet stream i.e to North in Northern hemisphere. Pilots should watch out for-

• CAT is likely to be more severe downstream of the confluence of two jet streams. The wind shear effect between the two jet streams in the region of confluence and immediately downstream is often highly turbulent.
• CAT in jet streams are more intense above, and to the lee of, mountain wave ranges. CAT should be anticipated whenever the flightpath traverses a strong jet stream in the vicinity of mountainous terrain. So a preflight briefing involving crew and passengers would help in mitigating the risks. Also, pilots should plan to drop speed to turbulence-penetration speed in such a region. Another tell-tale sign for turbulence in such a region is formation of lenticular clouds.
• Curving jet streams have turbulent edges and may be source of moderate to severe CAT. So, please study your meteorological charts carefully.

Thunderstorms

Turbulence, associated with thunderstorms, can be extremely hazardous, having the potential to cause overstressing of the aircraft or loss of control. Thunderstorm vertical currents may be strong enough to displace an aircraft up or down vertically as much as 2000 to 6000 feet. The greatest turbulence occurs in the vicinity of adjacent rising and descending drafts. Gust loads can be severe enough to stall an aircraft flying at rough air (maneuvering) speed or to cripple it at design cruising speed. Maximum turbulence usually occurs near the mid-level of the storm, between 12,000 and 20,000 feet and is most severe in clouds of the greatest vertical development.

Severe turbulence is present not just within the cloud. It can be expected up to 20 miles from severe thunderstorms and will be greater downwind than into wind. Severe turbulence and strong out-flowing winds may also be present beneath a thunderstorm. Microbursts can be especially hazardous because of the severe wind shear associated with them.

Thunderstorms can be easily identified visually during day time, by lightning during poor visibility or night conditions and with help of weather radar. The pilots should be able to warn the crew and passengers at least 10 min in advance to let them settle down and secure the cabin. Any CB cloud extending beyond 30,000 ft should be avoided. The weather radar should be used for weather avoidance and not for negotiating through the weather.

What should passengers do to avoid injuries?

The majority of passengers seriously injured by turbulence weren’t wearing their seat belts because some of them were using the restroom or walking up or down the aisle. Injuries can also occur due to carry-on-luggage falling out of overhead bins and hitting people on the head, people stumbling or being tossed into seats or the sides of the cabin or food carts ramming into people. The same was also true for crew members, who were most commonly injured while preparing the cabin for landing or doing cabin service — like serving food or drinks or collecting trash. Thus a timely warning of at least 10 minutes could once again save all these people who had a valid reason for not being belted. Some tips for safety-

• Passengers can easily prevent injuries from unexpected turbulence by keeping their seat belt buckled at all times.
• Listen to the pilots and flight attendants. Avoid movement in cabin when seat belt sign is illuminated during flight.
• Pay attention to the safety briefing at the beginning of your flight and read the safety briefing card.
• Use an approved child safety seat or device if your child is under two.
• Prevent inflight injuries by adhering to your airline’s carry-on luggage restrictions.

AVIATION REGULATOR ROLE

The turbulence related incidents are on the rise. The injury to crew and passengers, structural damage to aircraft and flight delays related to weather leads to unwanted cost which runs into millions of dollars. The aviation regulator plays a very vital role in preventing such incidents-

• Improved data collection- Mandating reporting of each flight incident when vertical acceleration are exceeded beyond +1.8 and below -0.5. This will create a robust information on weather related information, turbulence and injury to passenger/crew and damage to aircraft.
• Encouraging pilots to file more reports via Pilot Report System (PIREPS) where pilots communicate weather conditions, including turbulence.
• Improving Real-Time-Information sharing. Training Air Traffic controllers to ask for PIREPs and sharing that information with other flights.
• Using Modern Technology- using systems like ACARS, ADSB positions and radar display to route aircraft around weather systems.
• Aircraft Manufacturers needs to develop new technology to detect CAT.

Turbulence leads to discomfort, fear and in very rare cases injury to passenger/crew or structural damage which is caused by wind, thunderstorms, the jet stream, proximity to mountains, and other factors. Sure it is terrifying when aircraft flies through a rough patch.
But a simple solution of keeping seat belt buckled can save you from lot of trouble later. Seatbelt is worth keeping buckled all the time, the same way you do it while travelling in a motor-car.

Be safe. Happy Landings.

Click on the links below to read my previous articles on similar subjects. Enjoy reading.