All Boeing 737 Max 8 and 9 aircraft will remain grounded at least until May after the fatal Ethiopian Airlines crash on Sunday, the US Federal Aviation Administration (FAA) has said.
The aircraft will not fly until a software update can be tested and installed, the US regulator said.
Sunday's crash, shortly after take-off from Addis Ababa, killed 157 people from 35 nations.
It was the second crash involving a 737 Max in six months.
Some people have pointed to similarities between the incidents, with some experts citing satellite data and evidence from the crash scene as showing links between Sunday's disaster and October's crash in Indonesia of the Lion Air jet that killed 189 people.
US Representative Rick Larsen said the software upgrade would take a few weeks to complete, and installing it on all the aircraft would take "at least through April".
The FAA said on Wednesday that a software fix for the 737 Max that Boeing had been working on since the Lion Air crash would take months to complete.
Meanwhile, investigators in France have taken charge of the crashed Ethiopian Airlines aircraft's black boxes as they attempt to uncover what caused the Boeing 737 Max disaster.
The Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA) received the flight data and cockpit voice recorders on Thursday.
The first readings could take days, but a lot depends on the boxes' condition.
Regulators across the world continue to ground the Boeing aircraft.
On Thursday, Russia, Japan and Tunisia banned the jet from their airspace. Late on Wednesday, the FAA told the country's airlines to ground their fleets, but was criticised for not doing it sooner.
Possible similarities between the accidents, focussing on the aircraft's anti-stall system, have shocked the aviation industry and raised questions over Boeing's, and the FAA's, insistence earlier this week the the Max 737 was safe to fly.
In addition to Max aircraft in service, about another 5,000 are on order from airlines. Garuda Indonesia said there was a possibility it would cancel its 20-strong order for Max jets, depending on what the FAA does.
A BEA spokesman said he did not know what condition the black boxes were in. "First we will try to read the data," the spokesman said, adding that the first analyses could take between half a day and several days.
There have been reports, including by Reuters, that there was a tussle over which safety authority would take the lead in examining the black boxes.
Reports said Germany was initially asked to conduct the analysis because Ethiopian Airlines had been unhappy at the way the Paris-based organisation had investigated a crash in Lebanon in 2010.
Britain and the US both have highly-respected crash investigation agencies.
Analysis: Theo Leggett, business correspondent:
How long the analysis by the BEA will take depends on a number of things.
First, the state of the recorders themselves. They are contained in very robust housings designed to withstand tremendous forces, and they are placed in the rear of the aircraft where they may be sheltered from the worst effects of an impact.
Nevertheless, they can still be damaged, particularly by intense fire. The investigators will need to extract the memory modules, basically circuit boards covered with memory chips, and carry out any necessary repairs.
The modules are designed so that information is spread across a series of chips. If one part is damaged, there should still be useable information elsewhere.
Once downloaded, the data also has to be read. Surprisingly, it is not recorded in a standard form - so investigators will need to know how to make it useable. That will need input from the airline itself.
If all goes well, the investigators will have access to thousands of pieces of data about the aircraft - not only what was going on on the fatal flight itself, but also on previous journeys.
They will also be able to hear what was going on in the cockpit, what the pilots said to one another, and if any audible warnings were sounding.
All of that should go a long way towards establishing the immediate causes of the accident - and finding out whether there really were common factors with the Lion Air crash.