Boeing began a series of long-delayed flight tests of its redesigned 737 MAX with regulators at the controls on Monday (US time), hoping to win approval and rebuild its reputation after fatal crashes that toppled its leaders and grounded the jet worldwide.
Pilots from the US FAA and Boeing landed around 2:15pm (local time) at King County International Airport, also known as Boeing Field, after a round trip to eastern Washington that included a high-speed system test and other manoeuvres over about three hours.
Reuters first reported the long-awaited certification test flights, scheduled over three days, were set to start on Monday, a pivotal moment in Boeing's worst-ever corporate crisis triggered by twin crashes that killed 346 people in Ethiopia and Indonesia.
Boeing shares closed 14.4 percent higher at US$194.49 on Monday, helping boost the Dow Jones Industrial Average.
After the flights are completed, the FAA must analyse reams of test data and approve new pilot training procedures, among other reviews, and would not likely approve the plane's ungrounding until September, industry and government sources say.
If that happens, the jet is on a path to resume US service before year-end, though the process has been plagued by delays for more than a year.
Boeing did not publicise Monday's take off, saying the FAA was leading the 737 MAX testing process. The business-as-usual atmosphere at Boeing Field illustrated a shift in Boeing's communications strategy on the 737 MAX since last year when it strained its relationship with the Federal Aviation Administration by issuing public statements that predicted the timeline for the jet's return.
The crisis has cost Boeing billions of dollars, slashed production and hobbled its supply chain, with criminal and congressional investigations still playing out. In December, Boeing fired Chief Executive Dennis Muilenburg after scrutiny into the jet's design and development tarnished its reputation with airlines and regulators.
The 737 MAX gaining FAA approval to return to commercial service is expected to spark a scramble by Boeing to determine the fate of hundreds of parked jets.
There are some 450 jets that Boeing is eager to deliver once the MAX is cleared to fly, though experts say the prospect of moving those quickly has been diminished by the coronavirus crisis.
Airlines have also grounded a further 385 jets in their fleets, and US carriers have said it will take them between 30 and 60 days after regulatory approval to prepare their jets and pilots for flight.
A central task for the FAA is to validate Boeing's upgrades to the MCAS anti-stall system faulted in both crashes, as well as perform a wide array of flight manoeuvres and emergency procedures, the FAA said.
The agency said it will "lift the grounding order only after we are satisfied that the aircraft meets certification standards".
After taking off from Boeing Field, the crew, which included Boeing Commercial Airplanes Chief Pilot Jim Webb, tested slow flight conditions between 12,000 feet and 15,000 feet, a person familiar with the flight said. Later, they boosted airspeed to 470 knots at 14,000 feet to conduct high-speed system tests, a person familiar with the flight said.
The goal was likely a test of whether pilots were able to manually adjust the tail's horizontal stabilizer at high speeds - a key focus during crash investigations because pilots struggled to make adjustments at high speeds while also trying to counteract MCAS.