The pilot of a missing Indonesian jetliner twice altered his flight path because of strong winds before disappearing from radar screens near Sulawesi's coastal town of Majene, an official said Friday.
As authorities expanded their search for the vanished Boeing 737 with 102 people aboard, including three Americans, U.S. investigators arrived in Indonesia to look into the apparent crash.
Adam Air Flight KI-574 did not issue a mayday Monday and there has been no emergency location signal to guide thousands of rescuers fanning out across Sulawesi's dense jungle terrain and over choppy Indonesian waters.
With no sign of the wreckage, they extended their sea search south toward the resort island of Bali, believing that five days of strong currents may have washed wreckage or bodies hundreds of miles from where the plane might have gone down, said Dudi Sudibyo, an aviation expert familiar with search and rescue efforts.
It remained unclear Friday what may have caused the flight to crash.
"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 due to metal fatigue or onboard explosion.
Pilots don't always issue a mayday during an emergency, he said, noting that 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."
The plane left Indonesia's main island of Java on Monday for Manado on Sulawesi but altered its flight path westward halfway into the two-hour flight after being warned of rough weather near the city of Makassar, said Eddy Suyanto, head of the search and rescue mission.
But when it ran into winds of more than 80 mph over the Makassar Strait, it changed course again, bringing the plane eastward toward land and then disappearing from the radar and losing contact over Majene, he said.
It is not clear why there have been no transmissions from the plane's emergency locator.
Smith speculated that it may not have been operational or — in the event of a crash at sea — that it could have sank into an underwater trench from which its signals could not be picked up.
A U.S. National Transportation Safety Board team arrived Friday to prepare for a possible crash investigation.
Three Americans were also onboard — Scott Jackson, 54, and his daughters 18-year-old Lindsey and Stephanie, 21, of Bend, Ore.
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 and Makassar, initially believed to be closer to the crash site.
Around 50 protesters gathered in the capital, Jakarta, dressed like bloodied air-crash victims, calling for the resignation of the transport minister who took more than 10 hours to admit that reports of survivors were unfounded.
"How could a plane disappear for several days without any clues whatsoever?," asked Junus Tombokan, 53, who was awaiting news about his nephew. "It's impossible."
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 the Maluku Sea just south of Manado — although an aerial search over the waters picked up no trace.
Adam Air is one of about 30 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 about maintenance of the leased planes.
Air navigation can be difficult in Indonesia, which spans 6 percent of the equator, 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 off course.Click here for FOXNews.com's Indonesia/ Pacific Center.