United Airlines discovers loose bolts on its Boeing 737 MAX 9 planes after Alaska Airlines incident

United's Boeing 737 MAX 9 planes are not currently in use

United Airlines announced Monday that it found loose bolts on its Boeing 737 MAX 9 planes, days after an Alaska Airlines plane of the same model lost a door plug mid-air.

In a statement obtained by FOX Business, United explained that its Boeing 737 MAX 9 aircraft will be suspended. The airline's 200 MAX 9 flights are also canceled.

"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," the company explained. "These findings will be remedied by our Tech Ops team to safely return the aircraft to service."

United said that it is still waiting for final approval from the Federal Aviation Administration on the inspection process.

WHAT TO KNOW ABOUT THE BOEING 737 MAX 9 PANEL THAT BLEW OFF IN MID-AIR

United flight takes off from Los Angeles

A United Airlines Boeing 737 MAX 9 airplane takes off from Los Angeles International Airport (LAX) as seen from El Segundo, California, on September 11, 2023.  (PATRICK T. FALLON/AFP via Getty Images / Getty Images)

Alaska Airlines also acknowledged encountering "loose" materials in a statement on its inspections on Monday night.

"As our maintenance technicians began preparing our 737-9 MAX fleet for inspections, they accessed the area in question. Initial reports from our technicians indicate some loose hardware was visible on some aircraft," the statement read.

On Friday, Alaska Air Flight 1282 was forced to make an emergency landing after a door plug blew out in the middle of its flight. Shares for Boeing and Spirit Aerosystems tanked after the incident.

The flight was around 16,000 feet in the air when the door plug blew off, en route to Ontario, California from Portland, Oregon. The cabin experienced depressurization, prompting the pilots to make an emergency landing at Portland International Airport.

FAA TO TEMPORARILY GROUND CERTAIN PLANES AFTER ALASKA AIRLINES DOOR BLEW OFF IN MID-AIR

NTSB official analyzes Alaska Airlines blowout

Investigator-in-Charge John Lovell examines the fuselage plug area of Alaska Airlines Flight 1282 Boeing 737-9 MAX. (NTSB / Fox News)

Alaska Airlines reported that no one was seriously injured in the incident. 171 passengers were on board.

On Saturday, the FAA directed airlines operating worldwide to conduct safety inspections of their 171 Boeing 737 MAX 9 aircraft. The only U.S. carriers that operate the model are Alaska and United.

"As operators conduct the required inspections, we are staying in close contact with them and will help address any and all findings," Boeing said in a statement to FOX Business on Monday. "We are committed to ensuring every Boeing airplane meets design specifications and the highest safety and quality standards."

Boeing 737 MAX 9

An Alaska Airlines Boeing 737 Max-9 aircraft grounded at Seattle-Tacoma International Airport (SEA) in Seattle, Washington, US, on Saturday, Jan. 6, 2024.  (David Ryder/Bloomberg via Getty Images / Getty Images)

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"We regret the impact this has had on our customers and their passengers," the company added.

FOX Business's Landon Mion, Eric Revell, Sumner Park and The Associated Press contributed to this report.