Europe's biggest airline said it will happily take United's 737 Max jets if the US airline doesn't want them

• United Airlines' CEO said he's building an alternative plan without the Boeing 737 Max 10.
• It follows certification delays to the jet and frustration after the Alaska Airlines blowout.

Europe's biggest airline is defending Boeing as the American manufacturer deals with the fallout from the Alaska Airlines blowout.

During Ryanair's earnings presentation on Monday, CEO Michael O'Leary said: "I want today to extend, on behalf of Ryanair, my support to Dave Calhoun and Brian West, the CEO and CFO of Boeing."

"I know they're under attacks from certain quarters. They are doing a good job. They are turning that company around," O'Leary added.

Boeing has faced renewed scrutiny since a 737 Max 9 jet operated by Alaska Airlines lost its door plug in midair on January 5. The plane was delivered just 66 days earlier.

171 such jets were subsequently grounded, and only began flying again last Friday following inspections.

Scott Kirby, the CEO of United Airlines — the largest operator of the Max 9 — had strong words for Boeing last week as he implied a move away from the manufacturer.

O'Leary said if that happens, Ryanair will take on the orders.

Kirby told CNBC the grounding was "probably the straw that broke the camel's back" so he was building an alternative plan without the Boeing 737 Max 10.

He believes the single-aisle jet will be delayed at least five years behind schedule for certification.

"We are not canceling the order, we are taking it out of our internal plans. But Boeing is not going to be able to meet their contractual deliveries on at least many of those airplanes," Kirby said in an earnings call last Monday.

Ryanair's O'Leary, who's known for being outspoken, hit back at Kirby, saying his comments "weren't helpful."

"If United Airlines wants to delay or cancel any of their Max orders, Ryanair will be very happy to take them," he added.

The ultra-low-cost carrier currently has 300 Max 10 jets on order, compared to United's 150.

Earlier this month, O'Leary said he'd complained to Boeing over quality-control issues like finding a stray wrench under a plane floor.

Although he noted during the earnings call there was "a meaningful improvement in quality" on the last 12 jets it took delivery on before Christmas.