The pilot of the Ethiopian Airlines plane that crashed requested permission “in a panicky voice” to return to the airport shortly after take-off, the New York Times has reported.
Friday’s report cites “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, with its speed appearing unusually fast.
An airline spokesman has said the pilot was given permission to return, but the plane crashed minutes later outside the capital, Addis Ababa, killing all 157 people on board.
French authorities now have the plane’s flight data and voice recorders for analysis.
In Ethiopia, officials have started taking DNA samples from victims’ relatives to help identify remains.
Many countries and airlines around the world have grounded their Boeing 737 Max 8 planes.
The US-based aircraft manufacturer now faces the challenge of proving the jets are safe to fly amid suspicions that faulty software might have contributed to two crashes that killed 346 people in less than six months.
The decision to send the flight recorders to France was seen as a rebuke to the United States, which held out longer than most other countries in grounding the jets. The US National Transportation Safety Board sent three investigators to help French authorities.
Boeing executives announced that they had paused delivery of the Max, although the company planned to continue building the planes while it weighs up the effect of the grounding on production.
The US Federal Aviation Administration grounded the planes on Wednesday, saying regulators had new satellite evidence which showed the movements of Ethiopian Airlines Flight 302 were similar to those of Lion Air Flight 610. That flight crashed into the Java Sea off Indonesia in October, killing 189 people.
The Max jets are likely to be idle for weeks while Boeing tries to assure regulators around the world that the planes are safe.
At a minimum, aviation experts say, the plane-maker will need to finish updating software that might have played a role in the Lion Air crash.
Boeing said it supports the grounding of its planes as a precautionary step, while reiterating its “full confidence” in the safety of the 737 Max.
Engineers are making changes to the system designed to prevent an aerodynamic stall if sensors detect that the jet’s nose is pointed too high and its speed is too slow.
Satellite-based data showed that both the Ethiopian Airlines and Lion Air planes flew with erratic altitude changes that could indicate that the pilots were struggling to control the aircraft. Both crews tried to return to the airport.
How long the planes stay grounded depends largely on what investigators find on the cockpit voice and flight data recorders, said Peter Goelz, a former managing director for the NTSB.
The Max is the latest upgrade to the Boeing 737s. Because its engines were larger and heavier, they were placed higher and further forward on the wings. That created concern that the plane might be slightly more prone to an aerodynamic stall if not flown properly, so Boeing developed software to prevent that.
Investigators looking into the Indonesian crash are examining whether the software automatically pushed the plane’s nose down repeatedly, and whether the Lion Air pilots knew how to solve that problem by throwing toggle switches and cancelling the automated nose-down commands.
Ethiopian Airlines said its pilots received special training on how to deal with the Max’s anti-stall software.
At the crash scene in Hejere, about 31 miles (50km) from Addis Ababa, searchers continued to pick through the debris. Blue plastic sheeting covered the wreckage of the plane.
Anxious family members who had begun giving DNA samples waited for news on when identifications of remains would begin, and whether they would have anything to bury.
“We are not told what they have found so far,” Faysal Hussein, whose cousin was killed, told The Associated Press.
“We are sitting here like forever. We were taken to the crash site on Wednesday but not allowed to get a closer look. And then yesterday Ethiopian Airlines officials called us to a meeting but they don’t have anything to say. This is frustrating.”