French investigators were examining the black boxes from the Boeing 737 MAX aircraft that crashed in Ethiopia on Thursday, as the ban on the model went worldwide after President Donald Trump added the US to countries that have grounded the aircraft.
France's BEA air safety agency confirmed it has received the recorders from the plane that crashed shortly after takeoff from Addis Ababa on Sunday, killing all 157 people aboard.
BEA investigators will try to retrieve information from the cockpit voice and flight data recorders, which were damaged in the disaster.
Thousands of kilometres away, distraught families were demanding answers as they visited the deep black crater where the plane smashed into a field outside the capital, disintegrating on impact.
The plane was less than four months old when it went down just six minutes into its flight to Nairobi.
Ethiopian Airlines, Africa's largest carrier, sent the boxes to France because it does not have the equipment to analyse the data.
The information that black boxes contain helps explain 90 percent of all crashes, according to aviation experts.
On Wednesday, US authorities said new evidence showed similarities between the Ethiopia crash and that of a Lion Air flight in Indonesia in October that claimed the lives of 189 people.
The Federal Aviation Administration said findings from the crash site near Addis and "newly refined satellite data" warranted "further investigation of the possibility of a shared cause for the two incidents".
- Safety of 'paramount concern' -
An FAA emergency order grounded 737 MAX 8 and MAX 9 aircraft until further notice, effectively taking the aircraft out of the skies globally.
The move came after a growing number of airlines and countries had already decided not to fly the planes or ban them from their airspace until it was ascertained there are no safety issues.
Trump told reporters the "safety of the American people and all peoples is our paramount concern".
FAA acting chief Daniel Elwell said the agency has been "working tirelessly" to find the cause of the accident but faced delays because of the damage to the flight data recorders.
The new information shows "the track of that airplane was close enough to the track of the Lion Air flight... to warrant the grounding of the airplanes so we could get more information from the black boxes and determine if there's a link between the two, and if there is, find a fix to that link," Elwell said on CNBC.
Boeing's shares have sunk 10 percent since Sunday's crash, wiping more than $20 billion off the company's market value.
Boeing chief Dennis Muilenburg said he supported the US decision "out of an abundance of caution" but had "full confidence" in the safety of the plane.
The company continues its efforts "to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again," he said in a statement.
The MAX series is Boeing's fastest-selling model, but it is still relatively new with fewer than 500 in service.
There are 74 registered in the United States and 387 in use worldwide with 59 carriers, according to the FAA.
- Pilots concerns -
The accounts of the recent crashes were echoed in concerns registered by US pilots on how the MAX 8 behaves.
At least four American pilots made reports following the Lion Air crash, all complaining the aircraft suddenly pitched downwards shortly after takeoff, according to documents reviewed by AFP on the Aviation Safety Reporting System, a voluntary incident database maintained by NASA.
In two anonymous reports on flights just after the Lion Air disaster, pilots disconnected the autopilot and corrected the plane's trajectory.
One said the flight crew reviewed the incident "at length... but can't think of any reason the aircraft would pitch nose-down so aggressively."
It was unclear if US transport authorities review the database or investigate the incidents. However, the FAA said this week it had mandated that Boeing update its flight software and training on the aircraft.
Questions about the Lion Air crash have honed in on an automated stall prevention system, the MCAS, designed to automatically point the plane's nose downwards if it is in danger of stalling.
According to the flight data recorder, the pilots of Lion Air Flight 610 struggled to control the aircraft as the MCAS repeatedly pushed the nose down following takeoff.
The Ethiopian Airlines pilots reported similar difficulties before their aircraft plunged to the ground as they tried to return to the airport.
Boeing was criticised after the Lion Air crash for allegedly failing to adequately inform 737 pilots about the functioning of the stall prevention system.
Ethiopian Airlines CEO Tewolde GebreMariam said Sunday the flight's captain Yared Mulugeta Getachew, 29, was an experienced aviator with more than 8,000 flight hours.
BEA said any information about the investigation would come from Ethiopian Airlines, which itself tweeted that it would only communicate through social media and its website.
Andrew Hunter, a defence industry expert at the Center for Strategic and International Studies in Washington, said that while Boeing and the FAA had good track records on addressing safety concerns, sometimes the combination of automated systems and humans did not work smoothly.
"It is hard to get a system to work seamlessly with human beings," he told AFP.
"The fact the system was fighting the pilot was not an unintended consequence," because it should counteract a pilot error and correcting this is "challenging".
The Ethiopian Airlines plane was less than four months old when it went down six minutes into its flight to Nairobi.