Lufthansa's boss called delays to Boeing deliveries 'extremely annoying,' and it further highlights a growing dilemma for the aviation giant

• The CEO of Europe's biggest airline called Boeing's delivery delays "extremely annoying."
• The planemaker has slowed production to focus on safety in the wake of the Alaska Airlines blowout.

The CEO of Lufthansa has become the second airline boss in recent days to voice his frustration with Boeing over delivery delays.

In an interview with Swiss newspaper Neue Zuercher Zeitung published Saturday, Carsten Spohr was asked about the planemaker's delivery delays.

"This is extremely annoying and costs us a lot, a lot of money," he said.

By revenue, Lufthansa is Europe's biggest airline, and the fourth-biggest in the world.

Spohr's comments were published just days after the CEO of Emirates also expressed concerns about Boeing.

In an interview with CNBC, Sheikh Ahmed bin Saeed Al Maktoum told Boeing to "get your act together."

"I think they have to put a lot of pressure in order to make sure that they deliver to the customer whatever they promised," he added.

Boeing has been struggling since the Alaska Airlines blowout in January, working to slow down production to avoid quality-control errors but causing delays to aircraft deliveries as a result.

After announcing his resignation, Boeing CEO Dave Calhoun said the company needed to slow down production in order to focus on safety.

Following Al Maktoum's comments, the president of Boeing Global, Brendan Nelson, told Sky Arabia: "We've slowed down the rate of production to make sure that we can bring strength and quality to our supply chains, to stabilize those supply chains and to fortify our production system."

Other customers like Ryanair and United Airlines have already voiced their annoyance at the delays, to the extent that United is replacing its plans for the Boeing 737 Max 10 with some Airbus A321neos.

But Spohr is hopeful that Boeing will be able to recover and get the business back on track.

"I am sure that Boeing will get the problems under control," he told Neue Zuercher Zeitung. "The industry needs two strong providers. Everyone has an interest in Boeing being able to build great aircraft more reliably again soon."

Boeing declined to comment when reached by Business Insider.