(CNN) — The flight data recorders from Ethiopian Airlines Flight 302 have arrived at the French air accident investigation headquarters, after scores of airlines and countries grounded Boeing 737 Max 8s — the aircraft that crashed Sunday, killing all 157 people on board.

The two black boxes will be analyzed for potential clues into the fatal incident, the second crash involving a new Boeing 737 Max 8 aircraft in less than six months.

Last October, all 189 people on board the Lion Air Boeing 737 Max 8 were killed when the flight went down over the Java Sea in Indonesia shortly after takeoff.

A French Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA) spokesman said Thursday that the Ethiopian Airlines flight’s black boxes — the Digital Flight Data Recorder (DFDR) and Cockpit Voice Recorder (CVR) — would contain flight parameters as well as conversations in the cockpit.

“The truth about the crash is indeed contained in the flight recorders,” he said.

As the analysis gets underway, international concern over the possible dangers of Boeing’s 737 Max 8 aircraft continues to grow, particularly around similarities between Sunday’s crash and last year’s Lion Air crash in Indonesia.

Both were operated by well-known airlines with strong safety records, but the Lion Air flight went down 13 minutes after takeoff, while Sunday’s Ethiopian Airlines flight crashed just six minutes into its journey. The crash investigations in both incidents are ongoing.

On Wednesday, the US Federal Aviation Administration (FAA) announced it would ground all Boeing 737 Max planes indefinitely, pending the examination of the black boxes.

In its emergency order, the FAA said new information about Sunday’s crash “indicates some similarities” between the two disasters that “warrant further investigation of the possibility of a shared cause that needs to be better understood and addressed.”

The FAA cited “new evidence collected at the site and analyzed” and “refined satellite data” as to the reason behind its decision.

US officials and Boeing had argued to keep the planes operating in the wake of the crash but changed course shortly after Canada, one of the last countries allowing the planes to fly, joined some 47 other countries who had announced a ban on the plane by Wednesday.

Canadian Minister of Transport Marc Garneau was the first to reference the new satellite data. While not conclusive, Garneau said Canada had decided to ground both the Max 8 and 9 planes because there were similarities in the new data — specifically the vertical profile of the aircraft — and the doomed Lion Air flight that caused them to feel a threshold had been crossed.

Boeing said it remained confident about the safety of the jets, but that it recommended the shutdown itself “out of an abundance of caution and in order to reassure the flying public of the aircraft’s safety,” according to a statement from the company.

“We are supporting this proactive step,” Boeing CEO Dennis Muilenburg said. “We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again.”

Flight control problems

The pilot of the downed Ethiopian Airlines flight had “flight control problems” shortly before the fatal crash, according to the company’s CEO Tewolde GebreMariam.

“He was having difficulties with the flight control of the airplane, so he asked to return back to base,” GebreMariam said. He added that the pilot was granted permission to return to ground at the same time the flight disappeared from radar — just six minutes after takeoff.

While investigators search for clues as to the cause of the disaster, some aviation authorities and experts continue to draw parallels between the Ethiopian Airways and the Lion Air flight, noting that although the circumstances of these two crashes appear very similar, other explanations cannot be discounted at this early point in the investigation.

A preliminary report on the Lion Air Flight 610 crash said that data retrieved from the flight recorder showed the pilots repeatedly fighting to override a new safety system installed in the Max 8 plane — the Maneuvering Characteristics Augmentation System (MCAS).

In that flight, the MCAS system was responding to faulty data that suggested the plane’s nose was tilted at a higher angle than it was, indicating the plane was at risk of stalling, and pulled the plane’s nose down more than two dozen times.

According to the report, the pilots first manually corrected an “automatic aircraft nose down” two minutes after takeoff and performed the same procedure again and again before the plane hurtled nose-first into the Java Sea.

CNN aviation analyst David Soucie said at the time that the circumstances created by the plane’s automatic correction would have made pilot intervention “an impossible scenario to recover from.”

In November, Boeing issued an “Operations Manual Bulletin” advising airline operators how to address erroneous cockpit readings. It pointed airlines “to existing flight crew procedures to address circumstances where there is erroneous input from an AOA sensor,” a Boeing statement said. The FAA later issued its own emergency airworthiness directive that advised pilots about how to respond to similar problems.

Before the Lion Air crash, US pilots who fly the Boeing 737 Max had also registered complaints about the way the jet performed in flight, according to a federal database accessed by CNN.

‘Substantial’ similarities

A CNN review of reports filed in the Aviation Safety Reporting System identified 23 instances where crew members noted an issue, of any sort, with the 737 Max since October 2017, including reports where a pilot did not cite a specific model of the Boeing 737 Max series.

Many of these reports were categorized as “less severe,” however two of the reports highlight an unexpected descent of the aircraft. One report details an unexpected climb and another says there was a problem leveling off at the wrong altitude.

And many of the reports point to confusion with some part of the new aircraft, with those pilots saying they were unsure if the anomaly they were reporting was caused by a mistake they made or the aircraft. Some of the reports deal with issues other than flying the aircraft.

However, other pilot complaints from the federal database were far more incendiary, including one report that said it was “unconscionable” that Boeing, the FAA and an unnamed airline would have pilots flying without adequate training or sufficient documentation.

The same entry also charges that the flight manual “is inadequate and almost criminally insufficient.”

On Tuesday, Ethiopian Airlines CEO GebreMariam said that both pilots of Flight 302 had been trained and briefed on the FAA directive after the Lion Air crash.

“There was training” with emphasis “on MCAS and also on the flight controls in general,” he said.

But the “similarities are substantial” in both accidents, GebreMariam said, adding that there are a lot of questions to be answered about the airplane.

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