United Airlines will work around Boeing’s delivery delays to keep its growth plan moving, using smaller aircraft in place of the 737-10s that likely remain several years from entering service.

“The mixture of that growth had been reliant on [737-10s],” United CFO and EVP Mike Leskinen said at a Feb. 20 Citi Global investor event. “What you’re going to see now is much more [737-9] and A321 aircraft—the mix of which I don’t know yet. It depends on the prices.”

The airline’s United Next plan, unveiled in 2021, leans heavily on adding higher-capacity aircraft. The mostly Boeing carrier counted on the 737-10, the last and largest 737 MAX family variant, as a key part of its narrowbody growth. The airline started the year with nearly 500 orders and options for the model, which it would fly alongside 737-8s and -9s as well as A321neos as part of the carrier’s long-term narrowbody fleet.

But Boeing’s growing pile of problems with the FAA means 737-10 certification and first deliveries are not expected until well into 2025 at the earliest. That prompted United to remove the 737-10 from its fleet plan for the foreseeable future, CEO Scott Kirby said in January.

Another option is keeping some of the older aircraft that some of the new orders are slated to replace, including about 60 757s. But since Next includes a cost-reduction element, any unplanned heavy maintenance work will be carefully scrutinized.

“We have some options on the margin to extend the life of some aircraft,” Leskinen said, without elaborating. “It’s not my favorite option because some of the aircraft are ready to retire, but you’d have some option to do that.”

Even without aircraft life extensions, maintenance and the company’s tech ops division will factor into the Next plan’s efforts. Leskinen called out parts manufacturer approval (PMA) and working with other maintenance providers as areas worth exploring.

“I think we’ve got some opportunity to do better things there, be it with PMA parts or working with additional MROs,” he said. “So, I’m excited about that.”

“We have [an] opportunity [with PMAs], Leskinen continued. “Maybe we’ll talk about it more in upcoming investor day, but it’s an area where we have the opportunity to expand.”