CEOs of two of the US’ biggest airlines, United and Alaska Airlines, have criticised Boeing amid investigations into the 737 MAX 9 door plug blow-out incident, out mid-flight, earlier in January.

Alaska CEO Ben Minicucci said he was “angry” about the incident, which occurred on one of its flights, and called on the manufacturer to further outline what it will do to improve quality programs.

Seperately, United’s Scott Kirby has poured doubt on his airline’s order of 737 MAX 10s, describing the US Federal Aviation Administration’s (FAA) grounding of some MAX 9s as “the straw that broke the camel’s back.” 

In an interview with NBC News’ Tom Costello, Minicucci discussed the airline’s discovery of loose bolts during inspections of its MAX 9 fleet, saying it made him “mad” to see issues like that on brand new planes. 

He said: “It’s clear to me that we received an airplane from Boeing with a faulty door. Now the NTSB investigation is going to figure out why that was a faulty door, whether it was bad installation, missing hardware, a manufacturing issue, but there’s no doubt that Alaska received an airplane off the production line with a faulty door [plug].” 

Similarly, Kirby told CNBC that he was “disappointed that these manufacturing challenges do keep happening at Boeing” after United, which is Boeing’s biggest customer, reported that it was expecting low to negative profits in Q1 2024 as a result of the MAX 9 grounding. 

Kirby also said that the company was building an alternative plan for its future that did not involve use of the 150 MAX 10s it has on order, following years of delays and an ongoing certification process for the aircraft. 

The CEOs criticism of the US aviation manufacturing giant continues recent troubles for the company, which has seen increased scrutiny following the Alaska incident including increased oversight of its production lines by the FAA. 

In response to concerns, Boeing has increased its own quality inspections and reviews of its suppliers, along with allowing airlines that operate 737s to come in and overview its production line.