Boeing was close to software fix for 737 Max before Ethiopia plane crash

Boeing Co was agonisingly close to a software fix for its 737 Max jetliner when an Ethiopian Airlines jet plunged to the ground March 10, the second deadly crash in less than five months.

The US planemaker, working with regulators, has spent months refining the feature since flight data from the October crash of a Lion Air jet in Indonesia indicated that the flight-control system had repeatedly tipped the nose down before pilots lost control. The upgrade proved more complicated than the manufacturer initially estimated, according to a Boeing executive.

Among the challenges for Boeing flight-control engineers is girding against “unknown, unknowns,” the random and unlikely circumstances that could cause the so-called MCAS software to again overwhelm pilots, said Mike Sinnett, a Boeing vice president of product strategy and development. The updated system will never command more pressure on a stabilizer than pilots can counteract by pulling back on the control column, he said.