Shortly after the crash it was incorrectly announced that the aircraft and 12 survivors had been found.
Patrick Smith, a US-based airline pilot and aviation commentator, said a massive structural failure due to metal fatigue or an explosion could have led to the aircraft crashing.
"Whatever happened to the plane, it was likely rapid and catastrophic," he said.
He noted 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."
Indonesia usually searches for seven days after a disaster, but Susilo Bambang Yudhoyono, the country's president, has ordered that the search continue without time constraints.
Hatta Radjasa, the transport minister, said: "The president has given instructions for the search to continue and not be bound by time limits. He has called for the maximum effort from the search and rescue teams so that the plane will be found."
The plane left Indonesia's main island of Java for Manado on Sulawesi but altered course and turned westward half way into the two-hour trip after being warned of rough weather near the city of Makassar.
But when it ran into winds of more than 130kph over the Makassar Strait, it changed course again, bringing the plane eastward towards land, then disappeared from the radar, he said.
It is not clear why there have been no transmissions from the aeroplane's emergency locator.
Smith speculated it may not have been operational or, in the event of a crash at sea, that it could have sunk into an underwater trench from which its signals could not be picked up.
Nearly 3,000 soldiers, police and civilians have been following jungle tracks on Sulawesi, while sonar-equipped ships and a fleet of aircraft have scoured the sea over an area roughly the size of Ireland.
|Protesters have called for the resignation of|
Indonesia's transport minister [AFP]
With no sign of the wreckage, rescuers extended their search south towards the resort island of Bali, believing that in the event of a sea crash strong currents may have washed debris or bodies hundreds of kilometres away.
Teams are also patrolling coasts further northeast.
Authorities wrongly said on Tuesday that the wreckage had been found with a dozen survivors, causing further anguish to relatives camped out at airports and hotels in Manado and Makassar.
About 50 protesters gathered in the capital, Jakarta, on Friday dressed like bloodied air-crash victims, calling for the resignation of the transport minister over the erroneous reports.
Fandi, who had four relatives on the aeroplane and like many Indonesians only uses a single name, said: "All we do is watch television. Officials from Adam Air aren't able to tell us anything."