Fox News reports: Just days before the mysterious crash of Air France Flight 447 in the Atlantic Ocean, Brazilian authorities reportedly delayed a similar Air France flight from Buenos Aires to Paris after the airline received a bomb threat over the phone.

Police and officials at Buenos Aires’ Ezeiza Airport spent 90 minutes inspecting the threatened plane for explosives on the evening of May 27, but found nothing, according to a Brazilian news report.

During the search, passengers were not evacuated from the jet and later arrived safely at their destination in Paris.

A French accident investigator said Wednesday it’s unclear whether the chief pilot of Flight 447 was at the controls when the plane crashed into the Atlantic Ocean.

The head of France’s accident investigation agency also said he is “not optimistic” that rescuers will recover the plane’s black boxes, which are probably miles underwater.

Pilots on long-haul flights often take turns at the controls to remain alert. Asked whether the chief pilot was in the cockpit when the plane went down, the chief investigator told a news conference in France that there was no confirmed information either way.

He noted, “We don’t even know the exact time of the accident.”

He also told reporters there were no indications of a problem with the plane before it left Rio de Janeiro on Sunday night en route to Paris.

Military planes and ships from Brazil and France homed in Wednesday on the bobbing wreckage of Flight 447, as investigators tried to determine what brought the plane and its 228 passengers down in the middle of the Atlantic Ocean.

The planes stepped up overflights 400 miles northeast of the Fernando de Noronha islands off Brazil’s northern coast, where an airplane seat, a fuel slick and pieces of white debris were spotted Tuesday in the vast ocean.

Rescue boats from several nations were sailing toward the site to start the recovery.

Air France Flight 447 vanished Sunday night about four hours into its flight from Rio de Janeiro to Paris. The reason for the crash remained unclear, with fierce thunderstorms, lightning or a catastrophic combination of causes as possible theories.

French accident investigators leading the investigation were holding a news conference later Wednesday.