United Airlines finds loose bolts holding door parts on its 737 Max fleet

Jan. 8 (UPI) -- United Airlines said Monday it has found several instances of loose bolts holding down "exit plugs" on its fleet of Boeing 737 Max-9 aircraft similar to the one that blew off during an Alaska Airlines flight.

The airline said that after preliminary investigation of its fleet of 79 Max 9s, it discovered that some of the refrigerator-sized panels -- which are installed to "plug" optional exits in the plane's fuselage -- were improperly installed.

"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," United said in a statement issued to media outlets. "These findings will be remedied by our Tech Ops team to safely return the aircraft to service."

The Federal Aviation Administration ordered a temporary grounding of certain 737 Max aircraft over the weekend following Friday's incident in which Alaska Airlines Flight 1282 lost an exit plug on its rear fuselage shortly after taking off from Portland, Ore., International Airport.

The blow-out caused a pressurization problem and forced the aircraft to make an emergency landing. Passengers described hearing a "loud boom," followed by a fierce gust of wind when the incident occurred. No one was seriously injured in the mishap.

The National Transportation Safety Board is probing the incident. The agency announced Monday it has recovered the blown-out exit plug in Cedar Hills, Ore., and will examine it at the NTSB Materials Laboratory in Washington, D.C.

The FAA, meanwhile, assured the flying public it will not allow the affected aircraft to return to the sky until the issue is resolved.

"The FAA's priority is always keeping Americans safe," the agency said in a statement on Monday. "In that spirit, Boeing 737-9 aircraft will remain grounded until 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."