Indonesia's Adam Air Flight KI-574 took off on New Year's Day with 102 people. An hour into what should have been a short hop between islands, the pilot reported heavy winds. Then the plane vanished, sparking a massive search.

Thousands of soldiers battled rugged jungle terrain, a fleet of aircraft took to the skies and ships scoured the sea for a third day Thursday, spanning a 28,000-square-mile area — roughly the size of Ireland, or the U.S. state of California.

But by nightfall they had found no trace of the Boeing 737.

"We know nothing, whether it disintegrated in midair, flew into a storm or there were technical problems," said Nicholas Ionides, managing editor for Flight International Magazine in Asia. "We just don't know."

A top aviation official said the Adam Air plane that left Indonesia's main island of Java on Monday for Manado on Sulawesi island did not issue distress signals or complain of mechanical problems. The statements contradicted earlier reports and capped days of confusion.

On Tuesday, authorities wrongly claimed they had found the jetliner's charred wreckage and a dozen survivors, causing anguish among families of the plane's passengers, including an American man and his daughters.

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Hundreds of relatives have camped at airports and hotels in Manado, which was supposed to be the flight's final destination, as well as Makassar, initially believed to be closer to the crash site.

Many are grappling to understand how a 120-foot-long aircraft could vanish.

"It's impossible. How could a plane disappear for several days without any clues whatsoever," said Junus Tombokan, 53, who was waiting news about his nephew.

Iksan Tatang, the director general of air transportation, said that while the 17-year-old plane did experience severe weather halfway through its two-hour flight, there were no complaints from the pilot about navigation or mechanical difficulties.

But he told reporters Thursday that at least two signals from its emergency beacon — which is activated on impact or when a jetliner experiences a sharp, sudden descent — were picked up by a plane in the vicinity and by a satellite.

Eddy Suyanto, the head of the search and rescue mission, later put the number of so-called Elba signals at six, putting the last one over waters just south of Manado, but did not explain the discrepancy.

With no Mayday distress call, industry experts and pilots said it was possible the plane experienced a sudden, catastrophic mechanical failure, serious navigational problems, or even an explosion.

But Indonesia's transport minister cautioned against making guesses.

"I urge people not to speculate," Hatta Radjasa told reporters. "We must wait until the National Commission for Transportation Safety has located the ill-fated plane."

In the U.S. state of Oregon, the mother of two students who were on the plane with their father said she is holding out hope for them.

"There are times that I'm extraordinarily competent in all this, and times when I break down," The Oregonian newspaper of Portland quoted Felice Jackson DuBois as saying.

Stephanie Jackson, 21, and Lindsey Jackson, 18, were visiting their father, Scott Jackson, 54, Felice's former husband, who lives part-time in Indonesia.

Adam Air is one of at least a dozen budget carriers that have emerged in Indonesia since ex-dictator Suharto was ousted from power in 1998, when the industry was deregulated.

The rapid expansion has led to cheap flights to scores of destinations around the sprawling nation of thousands of islands, but has raised some safety concerns, since maintenance on the leased planes is reportedly poor.

Professional pilots discussing the accident in online chat rooms allege cronyism and political favoritism in Indonesia's aviation sector often undermine public safety. At the same time, large swaths of the country have radar blank spots, requiring pilots to radio through their coordinates to air traffic controllers.

That would be particularly dangerous if a plane suffered navigational difficulties — something Adam Air has experienced in the past.

Last year, one of its Boeing 737s flew off course along the same route and was lost for several hours until making an emergency landing at the small Tambalaka airstrip, hundreds of miles off course.

But until the flight recorder is found or radio transmission released, coming up with answers will be difficult, if not impossible.

"It is kind of strange," said Febrizal Lubis, a pilot for another Indonesian airline. "The plane was going along at 35,000 feet and then with no Mayday or distress signal it disappeared like that."

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