The first flight test of Boeing's 737 MAX since two deadly crashes - landed in Seattle on Monday.
The 737 MAX jet has been grounded worldwide for more than a year after twin crashes that killed more than 300 people.
This week's three days of test flights are critical for Boeing as it seeks to win approval for the aircraft's return to the skies.
Monday's trial included a high-speed system test and other maneuvers over some three hours.
The 737 MAX fallout has cost Boeing billions of dollars, slashed production and hobbled its supply chain.
Multiple criminal and congressional investigations are still playing out.
Boeing did not publicize Monday's take-off, saying the U.S. Federal Aviation Administration was leading the flight test process.
The FAA says a central task is to check Boeing's upgrades to the anti-stall system that faulted in both crashes and sent the planes into catastrophic dives.
Industry and government sources say the FAA will not likely approve the plane's ungrounding until September.
If that happens, the jet would be on track to resume U.S. service before year's end.
There are some 450 jets Boeing is eager to deliver once the 737 MAX is cleared to fly, although the global health crisis is expected to cause further delays.