The reason an Air France airliner crashed into the Atlantic this June with 228 people aboard remains unknown, local media reported on Aug. 31.

Investigators were still unable to explain the accident, Paul-Louis Arslanian, head of the French air accident investigation agency BEA, told reporters, adding that the third round of the search for the aircraft's black boxes would resume in the autumn.

More time was needed to analyze what happened in the four minutes before the crash of the plane, Arslanian said, adding that investigators would set priority targets and improve efficiency before conducting the new hunt for the black boxes.

The French investigation body said on Aug. 20 that it had suspended the second stage of the search after failing to find the black boxes of Air France flight 447.

The Airbus A330 jet plunged into the Atlantic en route from Rio de Janeiro to Paris on Jun. 1, killing everyone aboard. The wreckage of the plane and a number of bodies have been retrieved some 1,000 km off the Brazilian coast.

Automatic messages sent from the plane just before it crashed indicated that the plane suffered problems with air speed monitors, which gave false air speed readings to the plane's computers.

However, the BEA has denied this caused the crash, saying this was just a "factor".