Investigators at a lab in France and a field in Ethiopia are looking for clues into the second deadly accident involving Boeing's newest jetliner, while DNA testing has started to identify the remains of victims.
As the investigation proceeds, more details have emerged suggesting similarities between Sunday's crash of an Ethiopian Airlines Boeing 737 Max 8 jet and another deadly Max 8 accident in October.
Families of the Ethiopian Airlines victims have barely begun dealing with their grief. But Boeing investors on Friday cheered a report that the company might be closer than thought to fixing software that helps control the plane.
Here are five things to follow as the investigation continues.
Experts on Friday in France began analysing the so-called black boxes from Ethiopian Airlines Flight 302, which plummeted to the ground shortly after takeoff from Addis Ababa.
Preliminary satellite data suggests that the jet's flight path was similar to that of a Lion Air Max 8 that crashed on October 29 in Indonesia.
The Indonesian investigation focuses on whether flight-control software embedded in the plane automatically pushed the nose down repeatedly, and whether the pilots knew how to fix the problem.
Earlier this week, investigators searching the wreckage in Ethiopia found a part that controls tail surfaces used to make the plane rise or descend. The surfaces, called horizontal stabilizers, were tilting up, which would have caused the plane's nose to drop, according to a person familiar with the matter who spoke on condition of anonymity. The person was not permitted to disclose details of the investigation that have not been made public.
The 737 Max has flight-control software that can automatically tilt the stabilizers if sensors detect that the plane is in danger of losing aerodynamic lift from the wings, which is necessary to stay aloft. That is suspected in the Lion Air accident. It is too early to know whether the software or something else tilted the stabilizers up on the doomed Ethiopian plane.
Boeing shares were hammered all week but got a small bump Friday after a report by the Agence France-Presse news agency that the company will produce an upgrade to the Max's flight-control software in 10 days.
That would be quicker than expected. An airline industry official told The Associated Press that Boeing has indicated it is more likely to be two to four weeks. The official spoke on condition of anonymity because Boeing's conversations with airline officials were not intended to be made public.
Boeing declined to comment and Charles Bickers, an airline spokesman, referred the AP to the company's previous statement, which said only that the upgrade would be completed "in the coming weeks."
WHY IS IT TAKING SO LONG?
Boeing executives and technical experts briefed pilots at US airlines that fly the Max in November about the plane, less than a month after the Lion Air crash. They mentioned changes in the flight-control software, indicating that Boeing was already at work on a solution.
Boeing aimed to finish the work in April. Boeing has declined to say whether the Ethiopian Airlines crash gave new urgency to finish the work, but experts have said that is a safe bet.
"They were working toward a solution. They didn't expect the Ethiopians to lose their jet while all this was going on," said Alan Diehl, a former investigator for the National Transportation Safety Board.
Boeing won't comment on the time it has taken engineers to finish the work, but Diehl and industry officials familiar with the situation say it isn't as easy as upgrading an iPhone.
Engineers had to find out what the system was doing on the Lion Air flight, how the system's commands appeared to pilots, what changes needed to be made to software, manuals and training, and the best way to make those changes.
Then they had to write new software code, test it - first in the lab, then on a 737 Max simulator, finally in a flying plane. And they had to be sure that the modifications didn't affect other flying characteristics of the plane.
"Whenever you change this stuff you better be damn sure you don't create some other problem," Diehl said. "I think they are being very methodical."
COST FOR BOEING
The two deadly crashes and the worldwide grounding raise two risks for Boeing: financial losses and a reputational damage.
Analysts think Boeing can overcome both if the company convinces regulators relatively quickly that the problems with the plane and its flight-control software, and there are no more accidents.
Norwegian Air CEO Bjorn Kjos has said his airline will seek compensation from Boeing. Others carriers say it's too early for them to say whether they will because they cannot yet estimate lost revenue and extra costs. Those numbers depend on how long the planes end up parked.
Boeing already faces lawsuits over the Lion Air crash, and lawyers say the second crash strengthens their argument that Boeing knew the plane was defective and let it fly anyway.
Investigators haven't determined the cause of either crash, but Boeing would face large payouts to the families of passengers if the Max plane is found to be at fault.
Boeing has $7.6 billion in cash, but new revenue could face a hit because the company suspended deliveries of the Max on Thursday.
There are about 370 Max jets now parked at airlines around the world, including 72 in the United States. Because the Max is so new, it accounts for a small percentage of the global fleet of about 24,000 airliners.
In the US, Southwest is likely to be most affected because its 34 Max 8s represent nearly 5 percent of the carrier's fleet and a slightly higher percentage of the airline's passenger-carrying capacity. Southwest canceled 170 of its roughly 4,000 flights Friday, and "the vast majority" were due to the Max, said spokesman Chris Mainz.
American Airlines canceled about 85 flights Friday because of the groundings - some scheduled for its 24 Max 8s and others on planes being used to fill in for the now-parked Max 8s.
United Airlines, which has 14 Max 9s that are parked, canceled five flights scheduled for the planes on Friday and used other planes to add four flights to Hawaii for displaced passengers, said spokeswoman Erin Benson. The airline said in a securities filing Friday that the financial and operational impact of the grounding will increase if it lasts into the peak summer travel season.
Helane Becker, an airlines analyst with the Cowen Research financial services company said if the planes are grounded for a long time, ticket prices could rise because there will be fewer seats for sale if demand remains steady. Southwest experienced a bookings decline last year fall after one person was killed by a piece of engine debris on a flight last year.
The Max 8 crashes in Ethiopia and Indonesia killed 346 people.
Travel insurance companies expect a record number of claims from travelers whose flights scheduled on the Max planes have been canceled.