An hour after Adam Air Flight KI-574 took off on New Year's Day with 102 passengers and crew for what should have been a short hop between islands, the pilot reported heavy winds. Then, the plane disappeared.
Thousands of soldiers battled rugged jungle terrain, a fleet of aircraft took to the skies, and ships scoured the sea for a fourth day Thursday to search an area roughly the size of Ireland.
But so far they have found no trace of the Boeing 737.
"Whatever happened to the plane, it was likely rapid and catastrophic," said Patrick Smith, a U.S.-based airline pilot and aviation commentator, pointing to a possible massive structural failure or onboard explosion.
He said it was not unheard of that the plane did not issue a mayday.
"In many accidents there are no distress calls simply because the cockpit crew is too busy dealing with the situation rather than calling around for help," Smith said.
The plane left Indonesia's main island of Java on Monday for Manado on Sulawesi Island but lost contact with authorities halfway through the two-hour flight, after twice altering its course over water and land because of severe weather, said Eddy Suyanto, the head of the search and rescue mission.
Authorities wrongly said Tuesday the wreckage had been found with a dozen survivors, causing further anguish to relatives camped out at airports and hotels in Manado, which was supposed to be Flight KI-574's final destination, and Makassar, initially believed to be closer to the crash site.
Many wondered how a Boeing 737 could vanish.
"It's impossible," said Junus Tombokan, 53, who was awaiting news about his nephew. "How could a plane disappear for several days without any clues whatsoever?"
Iksan Tatang, Indonesia's director general of air transportation, said at least two signals from Flight KI-574's emergency beacon - activated on impact or when a plane experiences a sharp, sudden descent - were picked up by another aircraft in the vicinity and by a satellite.
Suyanto later put the number of emergency signals at six - saying the last one came over waters just south of Manado.
Adam Air is one of at least a dozen budget carriers that sprang up in Indonesia after 1998, when the industry was deregulated.
The rapid expansion has led to cheap flights to scores of destinations across Indonesia, but has also raised concerns because of reports of poor maintenance of the leased planes.
Professional pilots discussing the plane's disappearance in online chat rooms have alleged that cronyism and political favoritism in Indonesia's aviation industry has undermined public safety.
Air navigation can be difficult in Indonesia, which has been called the world's largest archipelago, because there are gaps in the communications systems. Last year, an Adam Air Boeing 737 flew off course on a stretch of the same route and was lost for several hours before it made an emergency landing at the small Tambalaka airstrip, hundreds of miles from where the plane was supposed to be.
Associated Press writer Slobodan Lekic in Brussels contributed to this report.
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