A French nuclear submarine is continuing to look.
U.S. Air Force Col. Willie Berges is the Brazil-based commander of American military forces supporting the effort. He says one ship towing a U.S. Navy listening device stopped searching Friday.
He says the other ship towing a device will end its search within hours.
Berges says the ships had "no success."
Flight 447 crashed into the Atlantic Ocean off Brazil's northeastern coast June 1. All 228 people aboard died.
Investigators say without the black boxes, it may be impossible to know for certain what caused the crash.