As the voice and data recorders from the second disaster involving a Boeing 737 MAX jet in five months arrived Thursday in France, safety investigators from the U.S. are flying over.
The probe centers on what sent the Ethiopian Airlines flight crashing back to the ground shortly after take-off and if there are any similarities with last year's crash of a Lion Air flight in Indonesia.
There's now a worldwide ban on the aircraft until it is deemed safe enough to go back in the air.
President Trump said he hoped it won't take long for Boeing to fix the problem.
But Trump's hope could be optimistic.
Boeing and the Federal Aviation Administration have to agree on the software fix and that's just the first step, says Reuters correspondent David Shepardson.
SOUNDBITE (ENGLISH) DAVID SHEPARDSON, REUTERS WASHINGTON CORRESPONDENT SAYING: "Then it has to be tested, approved and then training procedures have to be rolled out and it has to be actually implemented across the fleet.
So in a minimum, just finalizing the software upgrade will take weeks.
Lawmakers told us today that it would not be on all planes at least until the end of April, potentially longer.
Yesterday the FAA Administrator said the software upgrade could take a couple of months." And that's only if the investigation doesn't turn up any more problems. In the meantime, Boeing will keep making its best seller, but airlines are unlikely to accept - or pay for it - if still grounded.
Analysts estimate that could cost Boeing up to $2.5 billion a month in delayed payments.
And that doesn't include any reimbursement to airlines for flight disruptions.
Investors are bracing for legal and financial headaches, wiping out $25 billion in stock market value since the accident.
But the human toll of this tragedy can't be overlooked.
As more relatives reached the site of the Ethiopian crash - Thursday... scenes of uncontrollable grief...and frustration over how long it will take to identify victims. The crash so severe, the remains of the 157 on board are just charred fragments.
Full identification could take weeks or months.
Leaving relatives to wonder - how long before they can bury their dead.