How do we know theyâ€™re dead?

As it has unfolded, the mystery of missing flight MH370 and the incredible twists and turns in world news coverage.

"Heartbreaking" conclusion: Malaysian officials said no one survived MH370's crash into the ocean. Picture: AP Source: AP

HOW can they be so sure everyone is dead?

After nearly three weeks of wishy-washy statements from authorities, the families of MH370 passengers were startled out of their agony by an unusually blunt text message from Malaysia Airlines. The plane is in the ocean and all your relatives are gone.

Many couldn't accept it. And why would they? No bodies have been found. There hasn't been any confirmed wreckage.

Look out below: An RAAF AP-3C Orion returns from a mission in the Indian Ocean. Picture: AP Source: AP

Jose Salvador Alvarenga claimed he spent more than a year at sea -- a voyage of more than 12,500km. Picture: AFP Source: AFP

While aviation expert Neil Hansford is sure authorities "haven't told us everything" -- he believes the announcement was based on all the evidence available.

"The reality is that all of the available evidence suggests the poor devils are lost and the aircraft is lost," Mr Hansford told news.com.au.

SEARCH HALTED: FAMILY'S AGONISING WAIT FOR ANSWERS

That takes into account all satellite data released by Australia, France and China as well as the engine data breakthrough overnight.

He continued: "While we all hold out dreams for what happened... this at least gives them (the families) some closure - if they choose to take the closure."

The decision also allows for the progress of insurance payouts, Mr Hansford said, which cannot occur while the families are in limbo, even though the full story may not be known for several years.

Adrift at sea: Salvadorean castaway Jose Salvador Alvarenga washed up on the Marshall Islands on January 30. Picture: AFP Source: AFP

But still, how can Malaysian authorities say "beyond reasonable doubt" there were no survivors?

Stranger things have happened. Just last month, a "castaway" claimed he survived thirteen months adrift in the Atlantic on a leaky boat by drinking bird blood. Although it wasn't clear whether it was a miracle (or he was mad).

If there were MH370 survivors it would be a wonder even greater than the story of Stuart Diver -- the sole survivor of the Thredbo landslide in 1997.

Or that of Brant Webb and Todd Russell, the pair who were rescued from a collapsed Tasmanian mine after two weeks in April 2006.

Lifted: Stuart Diver was the sole survivor of the 1997 landslide. Eighteen died, including his wife Sally. Picture: News Corp Australia Source: News Limited

Survivors: Todd Russell and Brant Webb escaped Beaconsfield Mine with their lives. Source: NewsComAu

Oceanographer Erik van Sebille, from the University of NSW, said it would be near impossible to stay alive in the cold, 10-degree Celsius waters and rough conditions of the Indian ocean.

The area is in a notoriously gusty region of the south Indian Ocean with no land masses to slow the winds down.

"You'd really have no chance if you weren't in a life raft immediately," Dr Sebille said.

The search zone was initially identified as part of a 'southern corridor' stretching south from Kuala Lumpur. Picture: AMSA Source: Getty Images

Desperate hunt: Rescuers search for the missing jet in the Indian Ocean. Picture: AP Source: AP

These satellite pictures, provided by US satellite firm DigitalGlobe, were one of the first breakthroughs in the hunt for MH370. Picture: AP Source: AP

If survivors clung to plane debris it would have dispersed quickly throughout the ocean, he said. The seas would bump it around like a "pinball machine".

It has happened before. Back in 2009, a French teenager clung to life on the back of plane debris when a Yemenia Airlines Airbus crashed into stormy seas off the east African coast.

Baya Bakari, then 13, was the sole survivor of the disaster, holding on for more than 10 hours until rescue teams finally arrived. Cries for help faded away in the dark.

The bodies of more than 80 passengers, including Ms Bakari's mother, were recovered.

But after 17 days missing, experts doubt rescuers will even recover whole bodies of MH370 passengers.