Boeing is fixing a new software bug on the 737 Max

It involves a warning light for the horizontal stabilizer trim system.

By Alan Levin, Siddharth Philip and Christopher Jasper / Bloomberg News

The Boeing Co. has discovered a new software problem on the grounded 737 Max, but the company said that the flaw won’t set back the goal of returning the plane to service in mid-2020.

The planemaker notified U.S. regulators last month after identifying the issue during flight testing, according to an emailed statement Thursday from Boeing. Because of how the plane’s revised flight-control computers handle data, a light indicating that the stabilizer trim system wasn’t working was turning on when it wasn’t supposed to, the company said.

“We are incorporating a change to the 737 Max software prior to the fleet returning to service to ensure that this indicator light only illuminates as intended,” the company said.

The new software problem complicates Boeing’s efforts to return the Max to service by mid-2020, even if it doesn’t derail the recently extended timetable. The head of the Federal Aviation Administration, Steve Dickson, told reporters in London that a certification flight for the grounded jet could occur in the next few weeks — a key regulatory step in allowing the aircraft to start flying passengers again.

Dickson said during his remarks that the agency is evaluating the latest software issue.

The stabilizer trim warning light “had been staying on for longer than a desired period,” Dickson said, without providing more detail.

Aviation regulators are closely aligned on design requirements for the grounded 737 Max but may differ country by country on the jet’s operational return, Dickson said.

The divergence is likely even though authorities agree more than they disagree on the measures needed for the Max to resume flying after two fatal crashes, Dickson said.

The new issue on the Max involves an alert designed to warn when the trim system, which helps raise and lower the plane’s nose, isn’t working properly, according to two people familiar with the issue who weren’t authorized to comment on it.

One of the people familiar with the trim alert problem confirmed Boeing’s assessment, saying it’s not likely to change the projection of returning the plane to service because the company had built padding into the schedule.

The trim alert issue resulted from Boeing’s redesign of two flight computers that control the 737 Max to make them more resilient to failure, the two people said.

Boeing last month announced it doesn’t expect the plane to fly again until the middle of the year. After months of missed deadlines and growing tension with the FAA, the company said it was projecting a timeline that included extra room in case new issues arose.

The company was already at work on a separate software system known as Maneuvering Characteristics Augmentation System that was involved in the two fatal crashes on the plane that killed 346 people and led to the grounding last March 13.

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