Boeing is still pumping out more passenger planes than a year ago, but executives warned that a handful of threats loom on the horizon.

The plane maker's top seller, the 737 MAX, is moving off its Seattle-area assembly lines faster than a year ago. But Chief Executive Kelly Ortberg said the company has yet to hit the latest monthly target it set earlier this year.

"We are not stable yet at 47 a month," Ortberg said at an investor conference Wednesday. He said production of the in-demand jet was taking a little longer than expected, partly due to lagging wing production.

Regulatory work on the troubled 777X model could also "spill into next year" due to engine certification issues, Ortberg said. Airlines have waited years to take the long-delayed wide-body jet after a series of setbacks that have cost Boeing billions of dollars.

Ortberg said he still expects to deliver the first 777X models by the end of 2027, though a potential strike by union engineers and technicians as early as October would threaten that timeline.

Boeing shares fell 3.7% Wednesday.