May 21 (Reuters) - One passenger died of a suspected

heart attack and 30 others were injured after a Singapore

Airlines flight from London to Singapore hit severe

turbulence on Tuesday, forcing the Boeing 777-300ER jet to

divert to Bangkok, authorities said.

WHAT IS TURBULENCE?

Turbulence or pockets of disturbed air can have many causes,

most obviously the unstable weather patterns that trigger

storms, according to an industry briefing by planemaker Airbus.

The resulting water particles can be detected by weather radar.

Singapore Airlines did not immediately say what type of

turbulence was involved. Tracking service FlightRadar24 said

there were storms - some severe - in the area at the time.

...AND CLEAR AIR TURBULENCE?

Known by its abbreviation CAT, this is a sudden and severe

swirl that causes violent buffeting of a plane even where there

are no clouds, according to the Federal Aviation Administration.

Such invisible pockets of air can appear without warning and

are hard to predict. Mark Prosser of the University of Reading

said Tuesday's event most likely involved convective or

storm-related turbulence, but stressed it was too early to be

certain.

An investigation has been launched and experts stress

aircraft accidents typically involve a combination of factors.

HOW COMMON IS IT?

Turbulence-related incidents are common, according to a 2021

study by the U.S. National Transportation Safety Board.

From 2009 through 2018, it found that turbulence accounted

for more than a third of reported events and most resulted in

one or more serious injuries, but no aircraft damage.

Yet fatal turbulence in air travel remains extremely rare.

"It is a very unusual and rare event. As far as I can tell

it is over 25 years since a passenger was killed by commercial

airliner turbulence," said Paul Hayes, director of safety at

UK-based aviation data group Cirium Ascend.

The last fatal turbulence-related accident on Cirium's

database involved a United Airlines Boeing 747 in 1997.

HOW DO PILOTS RESPOND?

Crews plan ahead by studying turbulence and other weather

forecasts, which have improved over the years, loading extra

fuel when needed and monitoring weather radar during flight.

But sometimes violent CAT leaves little time to react.

"If it's unexpected then it's a bit late. You hope to get

warnings from other aircraft in the area and slow down to make

sure the effects are minimised," said retired pilot Hugh Dibley,

an expert on aircraft upsets at the Royal Aeronautical Society.

WHICH PLANES ARE BEST FOR TURBULENCE?

In terms of their structure, all modern commercial jets are

built to cope with forces many times those experienced

in-flight, Hayes said.

But according to Swedish turbulence-forecasting website

Turbli, the feeling experienced by passengers varies from plane

to plane and seat to seat.

Long planes can feel most turbulent at the back and the

ideal spot is around the centre of gravity, which is typically

just ahead of the wings.

Boeing's ( BA ) high-tech 787-9, with a "Gust Alleviation System"

from Honeywell, ranks first for handling turbulence,

according to Turbli. Next is the Airbus A340-500/600, though the

four-engined model is no longer widely used due to fuel costs.

The Boeing 777 family is widely seen as having a strong

safety record - excluding Malaysia Airlines MH17 which was

downed by a missile over Ukraine and the mystery disappearance

of MH370, both in 2014. It is equipped with traditional weather

radar but does not have the newer 787's alleviation system.

WHAT DOES IT MEAN FOR SEATBELTS?

U.S. airline pilot and flight attendant unions told Reuters

the incident highlights the importance of following crew

instructions and wearing seatbelt whenever seated.

But they cautioned that leaving the seatbelt sign on all the

time could erode its significance and that passengers could

start ignoring it.

Among the most exposed to injury are crew who must tour the

cabin to check seatbelts have been fastened when signs go on.

IS THERE ANY NEW TECHNOLOGY?

NASA says it is developing an early-warning system that

relies on ground-mounted infrasonic microphones to detect

clear-air turbulence hundreds of miles away.

Austria-based tech startup Turbulence Solutions says it is

developing technologies to eliminate up to 80% of turbulence.

But industry experts caution any new aircraft systems must

be proven to work to a high level of reliability and it takes

years of rigorous testing before technology can be validated.

Airlines must usually agree to foot the bill for any upgrades.

IS CLIMATE CHANGE TO BLAME?

A spate of turbulence reports has triggered a debate over

whether climate change may be causing more turbulence.

A report from the University of Reading last year suggested

turbulence could worsen with climate change.

"Our latest future projections indicate a doubling or

trebling of severe turbulence in the jet streams in the coming

decades, if the climate continues to change as we expect," said

Professor Paul Williams, one of the authors.

However, he told Fox News that while there seems to be a

strong correlation, more research is needed.

"It's too early to definitively blame climate change for the

recent apparent increases in turbulence. Increased media

coverage, aided by in-flight video footage from passengers'

mobile phones, may well be a factor," Williams added.