Confirmation that a wing flap found on an island in the western Indian Ocean is part of Malaysia Airlines Flight 370 would add a critical piece to the puzzle of the Boeing 777's disappearance 17 months ago. Malaysian Prime Minister Najib Razak delivered that confirmation Thursday, though French, U.S. and Australian investigators stopped just short of that, saying the part is from a 777 and acknowledging that Flight 370 is the only 777 missing. Examination of the part is continuing.

Here is what positively identifying the piece as a Flight 370 part would mean to the investigation:

___

IT WOULD SHOW THAT MH370 CRASHED

Authorities have long firmly held the opinion that the plane crashed, but the complete absence of any debris created lingering doubts not only with families of passengers and crew, but some accident investigation experts. The part, called a flaperon, would be the first concrete proof of a crash, although not everyone may consider it irrefutable evidence.

___

IT WOULD SHOW THAT IT CRASHED INTO THE INDIAN OCEAN

Again, while authorities were in no doubt that Flight 370 crashed in the Indian Ocean after veering far off its set northerly course from Kuala Lumpur in Malaysia to Beijing, they welcome tangible proof.

Tracking Flight 370's course during its final six hours has involved innovative methodology that has drawn evermore precise answers from scant data. The Boeing 777's last confirmed position was plotted by Malaysian military radar in the Strait of Malacca. From there, a team of experts from the United States, Britain and Australia have used seven satellite signals from a Flight 370 jet engine to a ground station to extrapolate where it went.

They initially narrowed the direction down to one of two vast arcs that ran through both the Southern and Northern hemispheres, from Kazakhstan to the southern Indian Ocean. Further analysis ruled out the northern arc, although not everyone is convinced that the plane was lost in the south.

Oceanographers agree that the discovery of wreckage on Reunion Island is consistent with the plane crashing in the Indian Ocean.

"The finding of the flaperon does not cast doubt on where we understand the crash happened," Australian government oceanographer David Griffin said.

___

IT WOULD NOT PINPOINT CRASH LOCATION

Authorities say that while the Reunion Island wreckage is consistent with their theory that the plane crashed within their 120,000-square-kilometer (46,000-square-mile) search zone more than 4,000 kilometers (2,500 miles) to the east, it does not prove that it did.

But they don't intend to change the boundaries of the current seabed search 1,800 kilometers (1,100 miles) west of Australia. Debris from that spot could have been carried to Reunion by Indian Ocean currents.

Griffin said that because there is "a lot of uncertainty in backtracking debris," it is not possible to retrace the flaperon's movements across the ocean to where the plane crashed 17 months earlier.

"You can never rule out other things, but you've got to go with what's most likely," Griffin said.

The search has covered nearly 60,000 square kilometers (23,000 square miles) since it started in October. The current search area is a long, narrow strip of ocean up to 6.5 kilometers (4 miles) deep over which Flight 370 is thought to have transmitted its final satellite signal. Authorities believe the signal was an automatic response to an electrical disruption probably caused by the plane running out of fuel.

___

IT MIGHT SUGGEST HOW MH370 CRASHED

Authorities are working on a theory that the plane ran out of fuel. But there are numerous theories about how the flight ended. 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 without a trace. Another explanation for why a six-week air and sea search covering 4.6 million square kilometers (1.8 million square miles) of the southern Indian Ocean surface early last year failed to find anything 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 and current head of accident investigation at Central Queensland University, said a single piece of wreckage could hold a multitude of clues. Any structural deformations 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, Dell said.

Analyzing 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."

___

LEARNING WHY IT CRASHED WOULD BE EVEN TOUGHER

Authorities struggle to find a logical explanation for why Flight 370 ended up at the bottom of a remote ocean. A mid-air explosion could leave clues on the flaperon, Dell said. Microscopic analysis of the surfaces could detect penetration of blast particles.

"You might be lucky and there might be tell-tale marks on this thing that could give you a clue to the failure sequence," Dell said. "I'd have to say that their luck would have to change for that to be the case," he added, because so far they've had none.