The U.S. Navy has picked up signals from the flight data recorders, or black boxes, of an Indonesian jetliner that crashed into the sea on New Year's Day with 102 people onboard, the U.S. Embassy said Thursday.

The U.S. Mary Sears located signals "on the same frequency of the black boxes associated with the missing airplane," a statement issued by the U.S. Embassy in Jakarta said.

Data from the flight recorders will be crucial in determining the cause of the crash, but retrieving them from the ocean floor at a depth of nearly 5,600 feet will likely be a difficult, expensive and lengthy operation.

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The Adam Air Boeing 737 went missing more than three weeks ago after reporting heavy winds off the western coast of Sulawesi while flying from Indonesia's main island of Java.

Three Americans — a man from Oregon and his two daughters — were onboard the plane.

Search teams have since found almost 200 pieces of debris — mostly small pieces of the wings, tail, cockpit and cabin — but no bodies.

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The embassy did not say when the black box signals were picked up or where on the ocean floor off Sulawesi they were coming from.

The hull of the aircraft has not yet been recovered, but the statement said that close to where the signals were coming from "the Mary Sears detected heavy debris scattered over a wide area" that was being analyzed to verify if it was from the missing aircraft.

Eddy Suyanto, the Indonesian air force commander in charge of the search and rescue mission, said he had not been formally informed of the ship's findings.

"One thing is for sure, up until this second, I have not received any report from the (Indonesian) liaison officers who were onboard the ship," he said.

Indonesia said earlier this week it did not have a submarine capable of retrieving the black boxes and would have to rent one.

Black boxes on commercial jetliners record crucial flight data such as a plane's speed and altitude as well communications between the pilots.

The embassy statement said that "having completed its mission" the Mary Sears would now depart Indonesian waters on Jan. 26.