(Irwin Fedriansyah ~ Associated Press)
The piece of the Boeing 737's tail was recovered Wednesday from the Makassar Strait off Sulawesi Island, said Eddy Suyanto, the head of search and rescue operations.
Suyanto said the serial number on the tail piece matched the one given to the search and rescue teams by Boeing.
No survivors or bodies have been recovered, Suyanto said.
On Wednesday, a U.S. Navy oceanographic survey ship was trying to determine whether large pieces of metal found in a separate discovery off Sulawesi's western coast were also wreckage from the plane.
An Indonesian vessel recently found the three pieces of debris on the Makassar Strait seabed after local fisherman told authorities they had spotted a low-flying, unstable aircraft in the area but lost sight of it after hearing a loud bang, naval officials said.
The USNS Mary Sears, which has sonar and satellite imagery capabilities, was called in to see if the metal could be the remnants of Adam Air Flight KI-574, which fell off radars in the area during 80 mph winds on New Year's Day, Suyanto saidWednesday.
The debris was roughly 2 1/2 miles from the West Sulawesi provincial capital of Mamuju at a depth of about 4,500 feet, he said.
Rear Admiral Moekhlas Sidik, commander of the Eastern Indonesia Fleet, said the Mary Sears had confirmed one of the objects was "round-shaped metal," but that more readings were needed to identify it.
The pilot of the Adam Air plane, which left Java island for the North Sulawesi provincial capital of Manado on Jan. 1, twice changed course because of rough weather but did not issue a mayday or report technical difficulties, officials said.
With no emergency location signal to guide more than 3,600 soldiers, police and volunteers searching in the island's dense jungles and surrounding seas, teams have fanned out over a nearly 30,000-square-mile area, almost the size of South Carolina.
A U.S. National Transportation Safety Board team arrived late last week and authorities in the United States were viewing satellite imagery of the island, the embassy said.
On Wednesday, searchers combed two areas recommended by U.S. investigators after they analyzed radar data from the day of the disappearance, Suyanto said.
After mistakenly claiming last week that the wreckage had been found with 12 survivors, officials were cautious in discussing the discovery of the underwater debris. It could be a sunken ship or something else, Suyanto told reporters.
Three Americans -- a man from Oregon and his two daughters -- were among the plane's 96 passengers. It was not clear if any other foreigners were on board.
Adam Air is one of about 30 budget carriers that sprang up in Indonesia after the industry was deregulated in 1998. The rapid expansion has led to cheap flights throughout Indonesia, but has raised concerns about maintenance.