Boeing 737 MAX certification flight tests to begin on June 29: Sources

Pilots and test crew members from the US Federal Aviation Administration and Boeing Co aim to kick off a certification test campaign for the 737 MAX on Monday, expected to last at least three days, people familiar with the matter told Reuters.

The flight test is a pivotal moment in Boeing's worst-ever corporate crisis, long since compounded by the COVID-19 pandemic that has slashed air travel and jet demand.

The grounding of the fast-selling 737 MAX in March 2019 after crashes killed 346 people in Ethiopia and Indonesia triggered hundreds of lawsuits, investigations by Congress and the Department of Justice and cut off a key source of Boeing's cash.

After a preflight briefing over several hours, the crew will board a 737 MAX 7 outfitted with special test equipment at Boeing Field near Seattle, one of the people said.

The crew will run methodically scripted mid-air scenarios such as steep-banking turns, progressing to more extreme maneuvers on a route primarily over Washington state. The flight plan could include touch-and-go landings at the eastern Washington airport in Moses Lake, and a path over the Pacific Ocean coastline, adjusting the course as needed for weather conditions and other factors, one of the people said.

Pilots will also intentionally trigger the reprogrammed stall-prevention software known as MCAS faulted in both crashes, and will likely perform a full aerodynamic stall, the people said.

The tests are meant to ensure that new protections Boeing added to the MCAS flight control system are robust enough to prevent the scenario pilots encountered in both crash flights, when they were unable to counteract the system and grappled with several factors like "stick shaker" column vibrations and other warnings, one of the people said.

Boeing and the FAA declined to comment.