Infighting among entities involved in the Ethiopian Airlines air disaster probe has hampered analysis of the plane’s damaged black boxes by France’s BEA air accident investigation agency, Fox News has learned.

Arguments broke out Thursday as the flight data recorder and the cockpit voice recorder arrived at the BEA near Paris for analysis, according to a source who spoke to American investigators there.

The source reported being told that the American investigators left the BEA Thursday night after 12 hours of "doing nothing."

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The United Nations International Civil Aviation Organization has protocols for examination, custody and cooperation among the investigators involved in a civil aviation accident but those protocols are being ignored, according to the source.

The source who spoke to the American investigators also reported being told that the crash site in Hejere had been ransacked by locals before it was secured.

“The scene has been badly compromised,” the source told Fox News. “Positioning is important and that’s been disrupted.”

The report of friction comes as the BEA said Friday that its analysis of the flight recorders had begun.

French officials have said it was unclear whether information could be retrieved due to the damaged condition of the recorders. Ethiopian authorities are leading the crash probe and it will also include the U.S. National Transporation Safety Board.

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Also Friday, The New York Times reported that the pilot requested permission "in a panicky voice" to return to the airport shortly after takeoff as the plane dipped up and down sharply and appeared to gain a startling amount of speed.

The report cited "a person who reviewed air traffic communications" from Sunday's flight saying controllers noticed the plane was moving up and down by hundreds of feet.

Sunday’s plane crashed minutes after takeoff outside Addis Ababa, killing all 157 on board, including eight Americans.

It was the second crash involving a Boeing 737 Max 8 jet in six months. A crash just after takeoff in Indonesia in October killed 189 people.

Countries -- including the United States -- have grounded the Boeing 737 Max 8 as Boeing faces the challenge of proving the jets are safe to fly amid suspicions that faulty software might have contributed to the two crashes. The company on Friday announced a possible software fix to be complete within 10 days.

The decision to send the flight recorders from the Ethiopia crash to France was seen as a rebuke to the U.S., which held out longer than most other countries in grounding the jets, finally giving the order Thursday afternoon. Peter Goelz, a former managing director of the NTSB who is now an aviation consultant, said that late call by the Federal Aviation Administration may indeed have been a factor.

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“I can’t speak for the Ethiopians,” Goelz said. “I’m sure that was under consideration that the FAA was adamant until they weren’t. I think Ethiopia wanted to choose an investigative partner that clearly didn’t have a dog in the fight.”

The Associated Press contributed to this report.