United Airlines and Alaska Airlines find loose bolts in Boeing jets during inspections

United Airlines on Monday (Jan 8) said that they found loose bolts while carrying out inspections of the Boeing 737 Max 9 fleet after a door plug had blown out from an Alaska Airlines plane over the weekend. The airlines said that they found that the bolts required "additional tightening" during inspections of Boeing 737 Max 9s.

The airlines started the inspections after a section of the fuselage fell from an Alaska Airlines 737 Max 9 on Friday (Jan 9).

United Airlines said that "installation issues" related to door plugs would be "remedied" before the particular aircraft is brought back into service. Around 171 planes of a similar type will remain grounded by the US regulator.

United Airlines, in a statement, said, "Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug - for example, bolts that needed additional tightening."

Alaska Airlines also said on Monday (Jan 8) that some loose hardware was found by its technicians in the door plug area on some of its Boeing 737 MAX 9 fleet. "As our maintenance technicians began preparing our 737-9 MAX fleet for inspections, they accessed the area in question," said Alaska Airlines.

"Initial reports from our technicians indicate some loose hardware was visible on some aircraft," it added.

The door plug is part of the fuselage and has a window which can be used as an emergency exit in some specific configurations. In a rare incident, the door plug of an Alaska Airlines plane had fallen off mid-air from Alaska Airlines' Boeing 737 Max 9 when it was flying over the US state of Oregon and landed in the backyard of a teacher's home. An emergency landing was made by the plane and none of the passengers or crew faced serious injuries.

United Airlines cancels 200 flights

The majority of Boeing 737 Max 9s, which fly in the United States, are operated by Alaska and United Airlines, while jets of the same model for inspections have been grounded by Turkish Airlines, Panama's Copa Airlines and Aeromexico.

United Airlines said that 200 flights have been cancelled by them on Monday and significant cancellations are expected on Tuesday. "We have been able to operate some planned flights by switching to other aircraft types, avoiding about 30 cancellations each on Monday and Tuesday," United Airlines said.

Watch:Alaska Airlines flight makes emergency landing after window blowout mid-flight

Meanwhile, the Federal Aviation Administration (FAA) on Monday (Jan 8), said that it provided a checklist which should be adhered to by the operators during inspections. The FAA, in a statement, said that all 737 Max 9 aircraft will remain grounded till operators "complete enhanced inspections which include both left and right cabin door exit plugs, door components, and fasteners".

"Operators must also complete corrective action requirements based on findings from the inspections prior to bringing any aircraft back into service," the statement added.

(With inputs from agencies)