Malaysia Airlines flight MH370 took off from Kuala Lumpur heading for Beijing on March 8, 2014 — and vanished.

Today, nearly 12 years later, a new search is set to begin.

So, what do we know, is the new search likely to find new evidence more than a decade after the flight went missing and with satellite technology how does a commercial aircraft disappear?

'Goodnight, Malaysian three seven zero'

The disappearance nearly 12 years ago of Malaysia Airlines flight MH370 with 239 people on board remains one of the world's greatest aviation mysteries.

The Boeing 777 went missing on its way from Kuala Lumpur to Beijing on March 8, 2014. 

There were seven Australians, more than 150 Chinese passengers, and 50 Malaysians on the flight, as well as citizens of France, Indonesia, India, the United States, Ukraine and Canada.

Satellite data analysis showed the plane likely crashed somewhere in the southern Indian Ocean, off the coast of Western Australia. 

However, two major searches failed to come up with any significant findings.

The last transmission from the plane was about 40 minutes after it took off. 

Captain Zaharie Ahmad Shah signed off with "Goodnight, Malaysian three seven zero", as the plane entered Vietnamese airspace.

Shortly afterwards, its transponder was turned off, which meant it could not be easily tracked.

Military radar showed the plane left its flight path to fly back over northern Malaysia and Penang Island, and then out into the Andaman Sea towards the tip of the Indonesian island of Sumatra. 

It then turned south and all contact was lost.

What is happening with the new search?

A deep-sea hunt for the plane is planned to start today.

The search will be carried out by US-based marine robotics company Ocean Infinity, which signed a new "no-find, no-fee" contract with the Malaysian government and will be paid $100 million — but only if the wreckage is discovered.

Charitha Pattiaratchi, a professor of coastal oceanography at the University of Western Australia, has been involved with the search for MH370 since 2014.

Ocean Infinity is expected to search for 55 days, in a remote part of the southern Indian Ocean and will use technology that didn't exist during earlier attempts.

Professor Pattiaratchi told Radio National that Ocean Infinity had conducted a search several years ago from ship Seabed Constructor, using autonomous underwater vehicles, searching the parts of the seabed in the southern Indian Ocean.

"Now they have gone up a notch ... and they have built new ships, which are much more efficient," he said.

"Also, the technology in the sonar and analysis has improved."

Ocean Infinity will be searching for large pieces of debris, Professor Pattiaratchi said, like engines and other big, heavy parts of the aircraft, which are more likely to be still intact.