Faults were found during a 2007 inspection of the downed Yemenia Airways Airbus A310 plane, which is similar to the one pictured. However, the airline says the problems were mainly cosmetic. (Reuters)

Black boxes recovered from the Yemenia Airways flight that plunged into the Indian Ocean in June are damaged, hampering the search for a cause of the crash, said a Comoran investigator.

Mohamed Ali Abdou, who is assisting French experts from the Bureau of Investigations and Analysis, said on Friday that investigators are still trying to recover the information held in the flight's black boxes.

Experts began examining the boxes from the Airbus 310 plane on Monday.

Ali Abdou said the cause of the crash is still unknown.

The black boxes were fished out of deep waters northwest of Grand Comoros island late last month by underwater robots.

Yemenia Flight 626 from Paris to Moroni, the capital of Comoros, crashed into the ocean on June 30, killing 152 people. Only a teenage girl survived.