Brazil has ended the search for more bodies from the Air France jet that crashed into the Atlantic Ocean last month, calling the task “impossible,” but the search for the jet’s flight recorders will go on.

Brazilian and French searchers have recovered large chunks of debris and 51 bodies from Air France Flight 447, which disappeared with 228 people on board late May 31.

On Friday, Brazil’s air force and navy ended their search for more bodies or debris.

“The reason for this is the impossibility of finding survivors or bodies, which has always been the main focus of our search efforts,” Brazilian Air Force Col. Henry Munhoz said at a news conference.

But Munhoz said the search for the black boxes would continue “coordinated by France.”

Experts say the black boxes may be key to deciding what brought the airliner down. And signals from the voice and data recorders begin to fade after about 30 days.

“We’ll have a better idea July 1 on how much longer we’ll go,” said U.S. Air Force Col. Willie Berges, the Brazil-based commander of the American military forces supporting the search.

Berges said searchers were likely to keep going 12 to 15 days past the 30-day mark of the crash.

A French nuclear submarine and two French-contracted ships towing U.S. Navy listening devices are trolling a search area with a radius of 50 miles (80 kilometers) off Brazil’s northeastern coast where it is believed the plane crashed.

The black boxes send out an electronic tapping sound that can be heard up to 1.25 miles (2 kilometers) away.

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