The Alaska airline found loose bolts on many 737 MAX 9s during inspections following a recent midair incident on January 5|@JettRink1956|X

Boeing faces ongoing challenges with its 737-9 MAX aircraft as Alaska Airlines and United Airlines express frustration over the “door plug” fault.

Alaska Airlines CEO Ben Minicucci, during an NBC interview, voiced anger and disappointment, demanding Boeing improve its in-house quality programs.

The airline found new loose bolts on many 737 MAX 9s during inspections following a recent midair incident on January 5.

United Airlines, the world’s largest 737-9 MAX operator, revealed a substantial impact from the grounding, as the aircraft constitutes 8% of the airline’s capacity.

United, along with Alaska Airlines cast doubts on Boeing’s capability to deliver on other MAX family aircraft, including the yet-to-be-certified 737 MAX 10.

Both airlines cast doubts on Boeing’s ability to deliver on other MAX family aircraft. Preliminary inspections continue as the FAA works on a directive.