Investigators from the National Transportation Safety Board, the United States’ independent investigative agency, as well as the Federal Aviation Administration, will add their expertise to the investigation involving the Boeing 737 Max 8 aircraft, which was certified by FAA officials working with the American aviation giant.

The same Boeing model was involved in the Oct. 29 crash of a Lion Air flight that plunged into the Java Sea in Indonesia, killing all 189 passengers and crew onboard.

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Ethiopian Airlines chief executive Tewolde Gebremariam had said earlier this week that the boxes could go to the United States but then immediately added they would more likely be sent to Europe in the interests of proximity and speed.

The boxes were initially offered to Germany, but the country’s aircraft investigators declined to analyze them, saying they came from a new type of plane and a new type of software.

Ethiopia’s decision to then offer them to France came just after the visit of President Emmanuel Macron, who left Ethiopia on Tuesday.

Some experts suggested that sending the devices to Europe for examination, rather than to the United States, might minimize second-guessing in the fraught investigation, given that the plane was built by a major American manufacturer that has continued to tout the safety of its aircraft.

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(Boeing said Thursday that it had stopped delivery of all 737 Max jets. The company said it would continue manufacturing them, however.)

Similar decisions on where to send black boxes have been made in previous cases, said Jeff Guzzetti, a former NTSB investigator and FAA safety manager. Despite vast technical expertise in the United States, some “foreign countries would not opt to send to the U.S. because they were the ones who built the airplane,” Guzzetti said. “Many times foreign countries just have a good relationship with a certain other country.”

After a major airline disaster such as the one Sunday, which killed 157 passengers and crew onboard, investigators rush to recover the devices. They are required on all airlines around the world and are built to withstand fire, heavy impact and intense water pressure. When planes go down in the ocean, a pinger attached to the black box sends a signal that sounds like a grandfather clock ticking for about 30 days before its battery dies.

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Typically, experts say, it takes almost a month to provide a comprehensive analysis of the data in the recorders.

But depending on the level of damage, those looking into the crash should be able to begin analyzing the initial data within 24 to 48 hours, said Mark Millam, vice president, technical, at the Flight Safety Foundation, an international nonprofit organization that focuses on providing expert safety guidance to the aviation and aerospace industries.

The data recorder’s “high-precision data” will give investigators detailed information about the actual airspeed of the aircraft, the up-and-down motion of the wings, and the up-and-down motion of the plane’s nose, Millam said. Combining that with the voice recordings is “golden in terms of any accident investigation.”

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According to the BEA, raw data from the recorders is decoded, turned into graphs and “used to calculate the behaviour of the aeroplane.” The audio recordings are turned into transcripts and also “make it possible to interpret warnings and noises present in the cockpit,” the agency said.

The Ethio­pian Airlines devices were discovered quickly after the crash, leading some U.S. officials to hope the insights within them would help determine whether American authorities should ground the 737 Max jets. While Ethio­pian investigators have the ability to download information from black boxes, they lacked the tools to do so in this case given the extensive damage, according to the FAA.

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It is unclear why it took days for the devices to be given to international investigators with suitable equipment and experience.

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“The delay was inexcusable. . . . They should have had a decision of where they were going to go as soon as they knew the airplane crashed,” Guzzetti said. “Maybe it was because of political factors. Maybe it was because they simply didn’t know any better. Maybe it was because they were distrustful of other parties.”

Using satellite tracking data from a private firm, U.S. and Canadian officials identified parallels between the flight that crashed outside Addis Ababa and the Lion Air flight in Indonesia, leading to the FAA’s decision Wednesday to ground both the 737 Max 8 and the Max 9, another aircraft in the series. The U.S. decision came after much of the world had already grounded the plane.

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Aviation experts said the satellite data showed the Ethio­pian Airlines plane’s movements echoed those of the Lion Air plane. Both crashes involved relatively new 737 Max 8s. The two jets both struggled to gain altitude and appeared to ascend and descend several times before crashing shortly after takeoff.

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But that is still only one piece of a very complex puzzle, Millam said.

“I think the world will obviously want to know, were the airplanes being flown the way they were intended, the way the manuals and training systems said?” Millam said. “Investigators are also interested in whether there were any sorts of anomalies that could have produced these flight failures.”

The NTSB said its three-person team has arrived in France to assist with downloading and analysis. The agency has three investigators in Ethiopia.

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U.S. officials say Ethio­pian authorities are taking the lead in the investigation, per international protocol, but U.S. experts have been cooperating with their counterparts from the outset.

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Because the 737 Max 8 was built in the United States, the NTSB can send an accredited representative to the investigation. The U.S. delegation of experts also includes technical advisers from the FAA, Boeing and GE/Safran, the manufacturer of the engines.

“This is an Ethiopian investigation,” NTSB spokesman Eric Weiss said. “We will be helping to download and analyze the flight data recorder and the cockpit voice recorder” and continue the work in Ethiopia.

The data in the black boxes could help investigators determine if Sunday’s crash is related to an automated feature on the aircraft, hundreds of which were flown around the world until countries, led by China, began barring them from flying in their airspace Monday.

Investigators will be looking into whether the same malfunctioning sensor, coupled with an automated response from the aircraft’s software that stymied the pilots’ ability to control the Lion Air flight, contributed to the downing of the Ethiopian Airlines plane. Investigators have not determined a final cause of the Lion Air crash.

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In Ethiopia, the investigation continued Thursday. The NTSB investigators dispatched to France will work in coordination with those on the ground in Addis Ababa, the agency said.

The NTSB group is smaller than a typical go team that would be sent to a crash on United States soil, which could consist of a dozen to 25 people.

Typically, the on-site phase of a probe takes one to two weeks.

“Everyone goes back home after the wreckage has been completely examined and all the perishable evidence has been gathered,” Guzzetti said. “They start poring over the data that is coming out from the flight recorders. They start doing research. They have progress meetings and teleconferences.”

After investigators retrieve information from the black boxes, they will typically release some information from the cockpit recorders explaining what was happening with the airplane at the time of the crash and characterize the quality of the recording and what it might contain, Guzzetti said. But it remains unclear how state-owned Ethio­pian Airlines and the country’s civil aviation authorities will release information, which has thus far been somewhat scattershot.

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Black boxes have helped investigators examine many crashes and have led to significant improvements in airplane safety and pilot training. Some U.S. airlines began to use flight data recorders in the late 1950s, and the recorders quickly caught on in other countries.