United Airlines is 'deeply disappointed' in Boeing over delays to new plane deliveries, as another major customer warns it needs to get its 'act together'

• United Airlines' CFO said the airline is "deeply disappointed" in Boeing due to delays, per Reuters.
• It is reportedly looking to buy more Airbus jets due to delays for the 737 Max 10.

Airlines are getting frustrated with Boeing due to delivery delays.

United Airlines is "deeply disappointed" in Boeing, its chief financial officer, Mike Leskinen, said during a Tuesday conference, Reuters reported.

His comments come after CEO Scott Kirby warned Boeing that United could change its plans due to delays to the certification of the 737 Max 10, the longest version of the single-aisle jet.

"The Max 9 grounding is probably the straw that broke the camel's back for us," he told CNBC in January. "We're gonna build an alternative plan that just doesn't have the Max 10 in it."

United — which is Boeing's biggest customer — has 277 Max 10 jets on order with options for another 200, Leskinen said in its fourth-quarter earnings call last month.

But on the same call, Kirby said: "Boeing is not going to be able to meet their contractual deliveries on at least many of those airplanes."

That creates problems for United's plan to expand its capacity with 800 new jets by 2032.

During a conference hosted by banking giant Citi on Tuesday, Leskinen said that instead of the Max 10, United would have more Max 9 and Airbus A321neo jets, per Reuters.

Earlier this month, United had to briefly ground its five A321neos as it waited for an exemption to keep the "No Smoking" sign permanently illuminated on the planes due to a peculiar FAA rule.

It looks like United is set to do more business with the European manufacturer. Kirby recently flew to Toulouse, France — where Airbus is headquartered — to discuss a potential deal, Reuters reported.

Concerns about Boeing's delays were also expressed by Michael O'Leary, the CEO of Ryanair, which is Europe's biggest budget airline, and operates almost exclusively using Boeing 737 planes.

O'Leary told Reuters on Tuesday Ryanair expects to be at least seven jets short this summer.

"We still think it's somewhere between seven and 10 but there's a risk it could be worse than that," O'Leary said. He added that it depends on the outcome of a review by the Federal Aviation Administration, launched due to last month's Alaska Airlines blowout.

"The [Boeing] management team in Seattle don't appear to have a grip on the situation at the moment," the Ryanair boss told Reuters.

He added: "We would like to see some a more expeditious outcome coming from both the FAA oversight and then Boeing ... getting their act together."

Boeing did not immediately respond to a request for comment from Business Insider, sent outside US working hours.