Terror theories scuttled as experts say wing part is from lost plane.

Confirmation that a wing part came from the missing Malaysian Airlines aircraft establishes that Flight 370 crashed somewhere in the Indian Ocean, laying to rest conspiracy theories that it was diverted to a desert island by hijackers or spirited off to a foreign country for use as a political bargaining chip.

Last night Malaysian Transport Minister Liow Tiong Lai added extra detail to what is known about the piece: one of the sealants on the part and the paint colour match "with our maintenance records".

Analysts say the investigators will examine the piece with microscopes to gain insight into what caused the plane to go down on March 8 last year.

It is hoped that will show how the piece - a flaperon - detached itself from the wing, or whether it shows traces of an explosion or fire.

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Australian aviation expert Neil Hansford said the flaperon snapping off gave pointers on how the jet entered the water. "What it does show is that the aircraft has gone into the water in a controlled-type crash and as the engines have hit the water, they've sheared off and this part is straight behind one of the engines," he said.

"All you can say it proves is that MH370 definitely crashed into the southern Indian Ocean and it also proves that the search area as identified by the Australian experts ... is appropriate."

Images of the flaperon appear to show slight damage to the front and a ragged horizontal tear across the back, CNN reported. It said one group of independent observers had said the damage indicated the piece came off while the plane was in the air.

The lack of damage to the front made it more likely the plane was in a high-speed, steep, spiral descent and the flaperon fluttered until it broke off, the group, led by American Mobile Satellite Corp co-founder Mike Exner, wrote in an assessment.

It is still not known why less than an hour into its journey from Kuala Lumpur to Beijing, MH370 turned back from its original flight path and headed in an opposite direction before turning left and flying south over the Indian Ocean for hours.

The flaperon find does not give much help to the search for the rest of the aeroplane and the remains of the 239 people who were on board.

The dean of the school of social work at the University at Buffalo, Nancy Smyth, said the confirmation was important to the families, but added: "For the families, in an ideal world it would not be finding a wing fragment, but it would be finding bodies. "So much of our grieving process involves physicality - seeing a body in a coffin. Without that, it is very hard to start the grieving process."

Most of those on the plane were Chinese, and many still refuse to believe their loved ones are dead.

"I don't believe this latest information about the plane, they have been lying to us from the beginning," said Zhang Yongli, whose daughter is missing.

"I know my daughter is out there, but they won't tell us the truth."

Bao Lanfang, 63, whose grandson was also on the plane, said, "Everyone has been lying to us", before collapsing on the floor and crying outside the Beijing offices of Malaysia Airlines.

Australia has said the find will not affect its sonar search of a 120,000sq km expanse of seabed more than 4000km east of Reunion Island, where the flaperon was found last week. That search, which began in October, has covered almost half that area without finding any clues. Most of the plane is believed to be 2.5 to 4km below the ocean surface.

But even if the body of the plane is found, the cockpit voice recorder, which might have revealed what happened in the cockpit after the plane went off course northeast of the Malaysian coast was on a two-hour loop, and the plane is estimated to have flown for about eight hours before crashing. Anything said as the plane diverted would have been recorded over by the time it went down.

But the flight data recorder, could give important details to help authorities determine what ultimately caused the plane to go down.

Experts who theorise that the plane was diverted by cockpit crew or hijackers point to several actions that occurred before the plane disappeared from radar. Notably, the plane turned off its intended flight path, ultimately heading for the Indian Ocean, and it appeared electronics that enabled the plane to be tracked were deliberately turned off.

Malaysian Prime Minister Najib Razak made the announcement that the wing piece was from MH370 370. But French, US and Australian authorities stopped short of full confirmation, frustrating relatives with mixed messages. Malaysia Airlines said the conclusion was reached in Toulouse, France, by the French agency that investigates air crashes, BEA, the Malaysian investigation team, a technical representative from China and the Australian Transportation Safety Bureau.

What the experts say

On the possible cause:
CNN aviation analyst Mary Schiavo

"If they find characteristic pitting in the wing structure, in the metal or the composite, that indicates there was some sort of explosive device, or if they find residue, which is not likely [after] this long in the ocean. But they'll probably not be able to tell why the plane went down - only that it did, and the manner in which it did."

On the flaperon:
Australian aviation expert Neil Hansford

"What it does show is that the aircraft has gone into the water in a controlled-type crash and as the engines have hit the water, they've sheared off and this part is straight behind one of the engines. There should be at least one other flaperon from the other wing [floating around]. All you can say it proves is that MH370 definitely crashed into the southern Indian Ocean."

University of Southampton oceanographer Simon Boxall

"We would expect, given that crash site, the debris to be moved to the north with the West Australian current. It would then pick up what we call the southern equatorial current towards Madagascar and it would take between 15 and 18 months. La Reunion is an island not far off Madagascar so it's about spot on."

On the barnacles:
Hans-Georg Herbig, of the University of Cologne

"Proof that it is Lepas australis, which generally inhabits cool waters, south of 35 degrees south, would be the best indication of a southern flight direction of MH370."

What story could the piece tell?

Some analysts argue that the apparent lack of damage to the piece of wreckage indicates a controlled landing on the ocean by someone who wanted the jet to sink intact - to vanish.

Another explanation for why the sea search has found nothing is that the jet plunged into the water vertically - high dive-style - snapping off both wings but preserving the fuselage.

Yet another theory, supported by a flight simulator, is that an out-of-fuel Boeing 777 would belly-flop heavily tail-first, disintegrating on impact.

Geoff Dell, a former Australian Airlines air safety investigator said any structural deformations on a piece of equipment could indicate the angle of impact. Analysis of the forces needed to snap it free could indicate the destructive forces acting on the rest of the plane. Or it may be that the part was simply "spat out" as the wing broke up.

Analysing the destructive forces could give searchers a better idea of what they're looking for on the ocean floor, he said. "Are you looking for an airplane where the engine is the biggest bit because everything else has been trashed down to the size of that piece (of wreckage), or is it easy to break that bit off?" Dell said. "In which case the forces might be a lot less and so larger pieces of structure that are stronger will remain intact."

A mid-air explosion could leave clues on the flaperon, Dell said. Microscopic analysis of the surfaces could detect penetration of blast particles.

- Washington Post-Bloomberg, AFP, AP, AAP