Boeing Co. has identified a new software flaw in the grounded 737 Max that will require additional work, possibly further delaying the plane's return to service.
The company alerted the U.S. Federal Aviation Administration and is notifying customers and its suppliers, it said in an emailed statement. Boeing's best-selling jet was grounded on March 13 after two fatal crashes involving a flight-control system.
The issue involves how software on the plane checks itself to ensure it's receiving valid data, said a person familiar with the issue who wasn't authorized to speak publicly about it. It occurs when the system is initially starting up, the person said.
"We are making necessary updates and working with the FAA on submission of this change, and keeping our customers and suppliers informed," Boeing said in its statement. "Our highest priority is ensuring the 737 MAX is safe and meets all regulatory requirements before it returns to service."
The FAA didn't comment directly on the latest issue to arise on the problem-plagued plane. "We continue to work with other international aviation safety regulators to review the proposed changes to the aircraft," the agency said in an emailed statement. "Our first priority is safety, and we have set no time-frame for when the work will be completed."
The 737 Max is costing the plane-maker billions of dollars in losses. The software problem was discovered during the final validation review process of the updates being installed on the plane, the person said.
It's unclear how time-consuming the repair will be. Software systems on aircraft require a far higher degree of reliability and checks before approval compared to consumer products. But the issue could be relatively narrow and therefore not nearly as complex as other work on the software.
News of the flaw sent Boeing shares down as far as $323, less than $3 from their closing low after the second Max crash. The stock closed down 2.3% in New York at $324.15, the day's biggest loser on the Dow Jones Industrial Average. Boeing's long-term issuer default rating was downgraded by Fitch to A- from A.
The discovery has already pushed Boeing's work back by at least a week, said another person familiar with the matter who also wasn't authorized to speak about it. It's unclear how much longer it will take to complete fixes, the person said.
The issue is in the plane's flight-control computer software. It was confined to how it performs validation checks during startup and doesn't involve its function during flight, the people said.