Boeing's long-awaited 737 MAX 10 hit an unexpected wall Monday, as the Federal Aviation Administration paused the jet's final certification over a newly flagged software problem — days after the plane appeared to be on the verge of finally winning approval.

Boeing shares slid as much as 6.8% on the news, one of the stock's worst single-day drops this year, as investors weighed fresh doubts about delivery timelines for the largest member of the company's best-selling narrowbody family.

What Went Wrong

According to reporting from Bloomberg, the issue centers on the flight management computer's vertical navigation function, known as VNAV. Regulators are examining whether the system could misbehave in a specific scenario: when a jet has to abort a landing and "go around" for another approach, such as when an obstruction is blocking the runway.

Boeing had reportedly been just days away from securing FAA sign-off on the MAX 10 when engineers flagged the glitch. Now the plane's fate rests with the FAA's Corrective Action Review Board, which must decide whether the VNAV issue rises to the level of a genuine safety-of-flight concern that has to be fixed before certification — or before the smaller MAX 7 variant can even enter commercial service.

THE MAX 10 WAS DAYS FROM THE FINISH LINE WHEN THE GLITCH SURFACED

Money on the Line

The delay isn't just an engineering headache. Boeing has billions of dollars in deliveries and cash flow riding on the MAX 10 finally reaching airline customers, several of whom have waited years beyond original delivery targets. A prolonged review could push deliveries further into next year, squeezing an aircraft order book that already stretches out for years.

The MAX 10 is the largest and latest variant of Boeing's 737 MAX family, which has spent years under intense regulatory scrutiny following two fatal crashes in 2018 and 2019 and a 2024 door-panel blowout on an Alaska Airlines MAX 9 that triggered a fresh wave of FAA oversight. Any new software concern on the MAX line draws immediate attention from regulators and the flying public alike.

What's Next

Boeing said it is working with the FAA to resolve the review "as quickly as possible," but neither the company nor regulators have offered a new certification timeline. Airlines that have ordered the MAX 10, including United and Delta, are now watching to see whether the delay is a matter of days or drags into a longer redesign.