Here’s how wreckage from Malaysia Airlines Flight 370 could have floated thousands of miles away from the search area off the coast of Australia. (The Washington Post)

The cold case known as Malaysia Airlines Flight 370 has been jolted by a piece of flotsam that washed ashore, and now investigators are scrambling again.

Authorities in France plan to examine what appears to be part of a wing that was found on a beach on Reunion, an island in the Indian Ocean, to see whether it came from a plane that vanished without a trace 16 months ago.

There is suddenly a new direction and a specific task in a long-running investigation that has been forced by a lack of physical evidence to focus on satellite signals from the time of the disappearance and a slow, patient and so-far fruitless sweep of remote deep seas off Australia.

Does a barnacle-encrusted piece of debris lead back to the Boeing 777 that is at the heart of the case? The object will be flown from Reunion, a French territory about 2,800 miles from the search site, to Toulouse, France, for examination.

But aviation experts and amateurs the world over are already arguing that from the images shown on the Web, the part is indeed from a Boeing 777. Yet new questions are already flaring: There have been different descriptions of what appears to be a part number stenciled on the piece, which could be crucial to its identification.

“If it is from a Boeing 777, it can’t be from anything except MH370,” said Richard Aboulafia, an aviation analyst at Virginia-based Teal Group. (“MH” is an international designator for Malaysia Airlines). “I mean, no one else just happens to be missing a 777 in that region of the world.”

But even in that case, the discovery of the part doesn’t exactly solve the mystery.

“It’s consistent with an aircraft that went down in March 2014, in an area off the southwest of Australia; it all fits in with the search pattern,” said Simon Boxall, an oceanographer at the University of Southampton in Britain. “The problem is it doesn’t help us narrow the search down. We can’t say we can reduce the search area. The chances of finding key bits from Flight 370 on the seafloor are still very, very remote in such a vast area and in such deep water.”

The discovery triggered huge interest in Australia, which is leading and funding the search mission. Australian Prime Minister Tony Abbott said that technical experts might be able to narrow the search area if the debris is confirmed as having come from the missing aircraft.

“At last it seems we may be on the verge of some confirmation,” he told Sydney radio station 2SM on Friday. “This is by far the most encouraging sign so far.”

A concrete link to the missing plane could offer some measure ofclosure to the families of the 239 people who were on board — if those families are willing to accept the evidence. On Thursday, many were skeptical, or perhaps in denial.

Most of the passengers on the March 8, 2014, flight from Kuala Lumpur, the capital of Malaysia, to Beijing were Chinese, and in Beijing, several families said Thursday that they still believe, against the odds, that the missing passengers might be alive, or that this is another false alarm.

They called on the Chinese news media to stop printing “hearsay” and said they were not ready to accept that the wreckage found on Reunion may be a piece of the missing plane.

The families later issued a statement saying they were tired of hearing from officials with “99 percent confidence.”

“We want 100 percent confidence,” they wrote.

Authorities from several countries cautioned against drawing quick conclusions.

But Malaysia’s deputy transport minister, Abdul Aziz Kaprawi, told Reuters that the large, battered and barnacled item was “almost certain” to have been a wing component known as a flaperon from a Boeing 777. Others agreed with him.

Once investigators in Toulouse take the item apart, it is likely that they will be able to confirm what it is and say almost immediately whether it came from Flight 370.

“There are serial numbers on so many of the internal components of a plane — numbers that you can use to trace not just to the factory where it was made but to the lot number and when it was made,” said Peter Goelz, a former managing director of the National Transportation Safety Board.

Investigators will also be scrutinizing the part for signs of how it was torn away from the wing.

“You examine the fractures and tears under a microscope and see if it’s torn off a certain way,” Goelz said. “From that, you may be able to tell if the plane crashed nose first or flat” like a belly-flop.

And while time and currents will have washed away any blast residue, a pattern of little pits or gashes in the metal could indicate an explosion, he said.

Experts say that if the plane went down where they think it did — off the Australian coast — it is plausible that a fragment could have drifted as far as Reunion.

“It’s in the right direction for the current,” said David Gallo, an oceanographer who helped lead the underwater search for Air France Flight 447, which crashed into the Atlantic during a 2009 flight from Rio de Janeiro to Paris. Its black boxes were recovered nearly two years later. Gallo is now director of special projects at the Woods Hole Oceanographic Institution in Massachusetts.

“The ocean down there circulates like a big tub, swirling in a counterclockwise direction,” he said. “Less than half a mile an hour, over 500 days, it would have made that journey easily.”

But, he added, “We will have to wait and see.”

The man who found the debris, identified by the Associated Press as Johnny Begue, also found a piece of a suitcase nearby.

The lack of certainty, for now, only compounds the misery of the friends and family members who have been waiting, and waiting, for news. They have reason to be skeptical.

They have spent the past year locked in a nightmare: cloistered in a hotel for weeks waiting for news, told not to talk to the media and fed false information — and when they made too much noise, were reportedly beaten by Chinese police.

In the absence of verifiable facts, the rumor mill went wild. Some still think that the plane was intercepted, perhaps by Islamic extremists or the CIA, and that their relatives could be alive, waiting to be rescued.

“I think the plane was hijacked, that this was a political incident,” said Zhang Yongli — whose daughter, Zhang Qi, is missing — in a telephone interview Thursday.

The disappearance of Flight 370 “really looks like a conspiracy,” said Jiang Hui, whose mother was on the plane.

“Why haven’t they shown us the boarding footage? Why couldn’t they confirm if the plane landed somewhere else or not? What are they trying to hide?” Jiang said.

Several said they will not believe the news until it has been confirmed by multiple sources, including the Chinese government, which has said little so far.

“This kind of news happens quite often,” said Steven Wang, whose mother is among the missing.

“It still needs to be verified and confirmed by not only one party,” he said. “Then I can be convinced.”

Until then, Wang said, he still has a glimmer of hope.

Wan reported from Washington. Karla Adam in London; Liu Liu, Xu Jing and Xu Yanjingjing in Beijing; and A. Odysseus Patrick in Sydney contributed to this report.