Washington — French aviation experts on Friday began work on the heavily damaged black boxes from Sunday's Ethiopian Airlines disaster. The crash site is also providing new clues into what may have claimed 157 lives.

Sources told CBS News that investigators at the crash scene recovered the Boeing 737 Max's jackscrew, which helps raise or lower the nose. It was set to dive.

Investigators are getting a clearer picture of how Flight 302 was in trouble almost from the beginning of its brief final flight. The pilots were locked in a battle for control of the aircraft as it climbed and dropped by hundreds of feet.

The oscillating flight track is similar to the Lion Air crash in October.

"The similarity is in both accidents, you do have this pitching up and down of the nose. It's just in the Ethiopian case, it occurred right after takeoff and continued," said Jeff Guzzetti, former National Transportation Safety Board investigator.

Air traffic controllers were aware of the plane's flight path. Three minutes after takeoff, the pilot made his distress call, according to the airline's CEO.

"The pilot reported flight control problems," said CEO Tewolde GebreMariam.

Investigators hope the black boxes tell them whether the plane's sensors malfunctioned similar to Lion Air. That could explain data showing the plane was flying unusually fast after taking off.

In Washington, lawmakers are calling for an investigation into the Federal Aviation Administration's approval process for the 737 Max, and its relationship with Boeing.

"They are there to protect the flying public and the people on the ground. They're not there to protect any company, or any airline, or anybody else and I'm gonna be scrutinizing to make sure that there wasn't any undue influence," said Rep. Peter DeFazio.

The FAA stands behind the process which relies heavily on Boeing.