"During the search of the projected crash site of Adam Air Flight 574, the Mary Sears, using a Towed Pinger Locator, detected pingers on the same frequency of the black box associated with the missing airplane," the US embassy said in a statement.
After sweeping the ocean floor around the area, the ship found heavy debris scattered over a wide area and was analysing the data, it said.
The Indonesian head of the search mission said earlier this month that work to locate the airliner's main body and black box, in areas where metal objects had been detected, was being hampered by the extreme depths in the Makassar Strait.
A flight recorder can give off signals for 30 days to aid detection, but that from the Adam Air plane may be lying in waters as deep as 1,700 metres.
The 17-year-old aircraft was heading from Surabaya in East Java to Manado in northern Sulawesi when it vanished in bad weather.
The aircraft made no distress call, although the pilot had reported concerns over crosswinds.