"It is not yet confirmed,” stressed First Air Marshal Eddy Suyanto, commander of the airbase in the city of Makassar which is coordinating the search.
A US ocean mapping ship with sonar capability will arrive on Tuesday to aid in the search, Eddy said.
The USNS Mary Sears will be joined by at least four Indonesian vessels, including one with a mini-submarine for undersea observation.
Besides Sulawesi's western coast, the search covers the Toraja highlands in the centre of the island and an area south of the North Sulawesi provincial capital of Manado, where the plane was headed when it disappeared from radar screens.
Investigators say the plane experienced 130 kilometres per hour headwinds and storms halfway through the two-hour flight, forcing it to change course at least twice.
But the pilot did not issue a Mayday or report technical problems before the aircraft disappeared from radar.