USA bank Citi said it expected the grounding to eat into the profits of Southwest Airlines, which operates the world's biggest 737 MAX fleet, causing a plane shortage for the carrier and likely passenger compensation costs.
The Boeing 737 MAX 8 is a brand-new jet.
The black boxes from the Ethiopian craft, which was only a few months old and crashed minutes after takeoff, are being analyzed by the French authorities to determine the cause of the accident.
And Captain Chesley "Sully" Sullenberger - noted for his safe landing of a damaged plane on the Hudson River in NY without loss of life - questioned the lack of experience of the Ethiopian first officer on the doomed flight, who reportedly had only 200 hours of flight time.
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.
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.
Kent Krause is an attorney who specializes in aviation issues.
The Ethiopian Airlines pilots reported similar difficulties before their aircraft plunged to the ground.
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Jones added: "He's a young player and you need to bring young players through carefully". 'We don't need to rush him. I've got him on the right track.
According to Boeing, the software being implemented includes updates to the Maneuvering Characteristics Augmentation System, the automated system created to keep the plane from stalling.
"As you do that, you're kind of fighting back and forth". "It may end up in such a severe fashion that okay the next time he sort of let's go or think he's got it under control".
Despite Boeing and USA airlines insisting the planes were safe to fly, the FAA grounded the planes Wednesday. USA pilot unions said their pilots were aware of the software issue and knew how to overcome it.
American Airlines representatives say that no work is planned for these aircrafts.
Transport Canada issued a safety notice on Wednesday restricting commercial use of the aircraft, citing new information from satellite tracking data that suggested "a possible, although unproven" similarity to the deadly Lion Air crash involving the same aircraft in October.
Krause says other pilots around the world should have known as well.
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.
"All airlines in the world should be well aware of the problem", Krause said.