The still unexplained crash, just after take-off from Addis Ababa, followed another disaster involving a Boeing 737 MAX in Indonesia five months ago that killed 189 people. Though there is no evidence of links, the twin disasters have spooked passengers worldwide, led to the grounding of most of Boeing's 737 MAX aircraft, and sending shares in the world's biggest planemaker plunging.
The investigation may focus on an automated anti-stall system that dips the aircraft's nose down. Asrat Begashaw, a spokesman for Ethiopia Airlines, told Reuters the pilot had reported flight control problems - as opposed to external factors such as birds - and had requested to turn back to Addis Ababa.
"In fact he was allowed to turn back," he said, adding that a decision where in Europe to send the black boxes would be taken by Thursday. Authorities in France and Britain said they had not been approached yet. Multiple nations, including the European Union, have suspended the 737 MAX, leading to the grounding of about two-thirds of the 371 jets of that make in operation around the world, according to Reuters calculations.
Boeing has nearly 5,000 more on order. Even as many passengers sought reassurances from travel agents that they would not be flying on a 737 MAX, the United States held out against suspension and Boeing continued to affirm its "full confidence" in the model.
Nevertheless, Boeing shares fell 6.1 percent on Tuesday, bringing losses to 11.15 percent since the crash, the steepest two-day loss for the stock since July 2009. The drop has lopped $26.65 billion off Boeing's market value. Possibly presaging a raft of claims, Norwegian Air said it would seek recompense for lost revenue and extra costs after grounding its 737 MAX aircraft.
More than a dozen relatives of those who perished paid respects on Wednesday at the rural crash site where Flight ET 302 came down in a fireball. Workers set up tents decorated with white roses.
Given problems of identification of charred remains, it will take days to start returning them to families, probably weeks for some which will require dental or DNA testing. The victims came from more than 30 nations, and included nearly two dozen U.N. staff.
Of the top 10 countries by air passenger travel, all but the United States and Japan have halted flights of the 737 MAX. Egypt, Thailand, Lebanon and Uzbekistan on Wednesday joined them, and Ethiopian Airlines CEO Tewolde Gebremariam said Boeing should ground all such craft until safety is clear.
Resisting pressure, the U.S. Federal Aviation Administration's (FAA) acting administrator Dan Elwel said its review had shown "no systemic performance issues." PILOTS' CONCERNS
The three U.S. airlines using the 737 MAX - Southwest Airlines Co, American Airlines Group Inc and United Airlines - stood by the aircraft. The new variant of the world's most-sold modern passenger aircraft was viewed as the likely workhorse for airlines for decades. But October's Lion Air crash in Indonesia sparked a debate on automation, particularly over a software system designed to push the plane down to stop a stall during flight.
Boeing says it plans to update the software in coming weeks. Though there are no proven links between the two recent 737 MAX crashes, the United Arab Emirates' aviation regulator said on Tuesday there were "marked similarities" and China's regulator noted both occurred shortly after take-off.
In November, two incidents were reported to the NASA-run Aviation Safety Reporting Database that involved problems in controlling the 737 MAX at low altitude just after take-off with autopilot engaged, according to documents first published by the Dallas Morning News and verified by Reuters. "We discussed the departure at length and I reviewed in my mind our automation setup and flight profile but can't think of any reason the aircraft would pitch nose down so aggressively," one pilot said.
In another case, the pilot said: "With the concerns with the MAX 8 nose down stuff, we thought it appropriate to bring it to your attention." Boeing did not respond immediately to a request for comment, but it has previously said it provided appropriate information to pilots to use an existing procedure to handle the issue of erroneous data affecting the anti-stall system.
(Additional reporting by Aaron Maasho in Addis Ababa; Kumerra Gemechu in Gora-Bokka, Ethiopia; Omar Mohammed and Maggie Fick in Nairobi; Tim Hepher in Paris; David Shepardson in Washington; Jamie Freed in Singapore; Terje Solsvik in Oslo Writing by Andrew Cawthorne; Editing by Jon Boyle/Keith Weir)