22 injured after major turbulence hit SIA flight: A primer on air turbulence

A Singapore Airlines A380 passenger plane taking off on a runway at Changi International Airport in Singapore. PHOTO: AFP
A Singapore Airlines A380 passenger plane taking off on a runway at Changi International Airport in Singapore. PHOTO: AFP

On Oct 18, eight passengers and 14 crew were injured after major turbulence hit a Singapore Airlines (SIA) flight from Singapore to Mumbai.

It is not known how serious the injuries were, but all 22 received medical treatment when the plane landed.

The Straits Times gives you the lowdown on airplane turbulence:

1. How does air turbulence occur?

Air turbulence is caused when bodies of air moving at different speeds meet; the mixing of the air results in turbulence. It can also be created by a thunderstorm, or near mountainous areas, as these result in more disruption to the surrounding air.

Temperature differences between air masses can also form turbulence, the Temasek Polytechnic's Aviation Management & Services team told The Straits Times. An example of this is when hot air from the ground below meets the cooler air at higher altitudes.

2. How often does it occur?

Almost every flight will experience air turbulence to a certain extent, although how much is felt depends on the size of the aircraft.

3. How does a pilot know there is approaching turbulence?

Before a flight, pilots are guided by pre-flight weather reports, that help them to plan ahead and choose the best route. The Temasek Polytechnic's Aviation Management & Services team said turbulence is generally most likely to be present in the vicinity of adverse weather, which is why pilots will try to navigate around thunderstorm areas.

However, during the flight itself, the heads-ups are generic and pilots are reliant on other aircraft's reports.

"We generally don't get more than a general warning," Captain Chesley Sullenberger, retired US Airways pilot and aviation expert told USA Today in July.

This general warning is made available to the pilot when another aircraft flying at the same altitude reports to the nearest air traffic control that it encountered turbulence.

The pilot can then choose to either change the aircraft's altitude, or change the speed of the aircraft in order to minimise the turbulence.

4. Is there any form of turbulence that cannot be pre-empted?

Clear air turbulence, which is formed by the mixing of air in the jet-stream, near mountain ranges and sometimes occurs with cirrus clouds.

"You cannot see it, you cannot detect it on radar and you cannot accurately forecast it," wrote British pilot Steve Allright in an article in The Telegraph last March.

"It is the most dangerous kind," wrote Barbara Peterson in travel magazine Conde Nast Traveller in February, explaining that it can even occur in cloudless skies with perfect visibility.

Pilots' are therefore reliant on other aircraft passing through the same air space for information on clear air turbulence, which is either passed on directly to them or via air traffic control.

The pilot can then consider flying at an altitude where no bumpy alerts have been sounded, although that smoother altitude could be occupied by another aircraft also seeking to avoid the turbulence.

Another form of turbulence that cannot be pre-empted is wind shear, said Ms Alicia Ong, a lecturer from Ngee Ann Polytechnic's Aerospace Technology course.

"This is caused by the difference between the speed and direction of the wind," she said.

5. Who are most at risk during air turbulence?

Passengers who are not buckled in, or crew members who did not manage to take their seats. They may end up being tossed about the aircraft and injure themselves or others.

Another category of passengers who may get hurt are infants, especially if they are only being held in an adult's arms without anything tying them down. There have been news reports about the child flying out of his or her parent's grasp during air turbulence.

6. How can passengers protect themselves during air turbulence?

Stay in your seat with your seatbelt fastened. It should be secured tightly, instead of hanging loosely around your waist - that defeats its purpose.

If you really want to play it safe, you can request for a window seat or a middle seat rather than an aisle one. This is because aisle seat passengers are most susceptible to any food or drink that may be displaced or spill in the event of sudden air turbulence.

This was exactly what happened last year during a Singapore Airlines flight from Singapore to London, which experienced severe turbulence. The Daily Mail reported that the flight fell 20 metres, and left 11 passengers and one crew member injured. Not only so, but images of the mess show that coffee was splashed onto the ceiling of the aircraft, meal trays and food items were strewn all over the aisle, and seats were stained.

7. What are the consequences of not staying in one's seat or not buckling up?

In general, those who are thrown out of their seats when the plane hits a rough patch land themselves bruises and bumps especially on their heads.

Earlier this year, a United Airlines Flight travelling from Denver to Billings, Montana encountered turbulence and a passenger reportedly hit the ceiling so hard that she cracked the panel above her head.

There have also been some cases where passengers sustained broken limbs, or even died after the aircraft they were on went through turbulence.

In 1966, a British Overseas Airways flight 911 that was travelling from Japan to Hong Kong encountered severe turbulence when it was approaching Japan's Mount Fuji and crashed. All 124 people on board were killed.

In 1997, a United Airlines flight travelling from Japan to Honolulu experienced terrible air turbulence and dropped 30 metres. One woman died and 10 others needed to be warded.

The comforting big picture (for those who fly in the United States at least) is that the number of turbulence-related injuries remains small. The Federal Aviation Administration says there are between 30 and 60 cases of turbulence-related injuries each year. Two-thirds of that number are flight attendants, which means that only 20 passengers - out of the 800 million who fly each year in the United States - are injured due to turbulence, reported Conde Nast Traveller in February.

Sources: USA Today, Conde Nast Traveller, The Telegraph, CNN Travel, The Daily Mail, Britannica.com

brynasim@sph.com.sg