United Airlines Finds Loose Bolts on At Least 5 Boeing 737 Max 9 Planes

United Airlines has found loose door plug bolts on at least five of the Boeing 737 Max 9 planes, as airlines begin inspecting planes following the Federal Aviation Administration’s temporary grounding order.

The loose bolts were found during initial inspections of what is known as the “mid-cabin door plug” partway down the fuselage of the 737-9, according to maintenance logs viewed by Skift.

“LH Mid Cabin Emergency Exit Door Plug, Upper Forward Guide Fitting, Lower Attach Bolts (2 ea.) are loose,” reads one of the reports, which was dated January 8.  

Four of the planes were delivered to the airline in 2023, and one in 2022.

“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,” said a United spokesperson.

It is unclear if the loose bolts identified in United’s inspection were also identified as part of the inspection guidelines Boeing provided on Monday. The FAA has confirmed Boeing’s guidelines as the “method to comply” with to return 737-9s to service.

In a statement late Monday, Alaska said it also found issues in initial inspections.

“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,” Alaska said.   

Boeing did not respond to a request for comment.

The news that United had discovered instances of loose bolts was first reported by The Air Current.

The mid-cabin door plug on an Alaska’s 737-9 detached from the plane after a sudden decompression shortly after takeoff on Friday.

On Saturday, the FAA temporarily grounded all 737-9s with door plugs pending inspections.

“This appears to be a manufacturing quality escape as opposed to a design issue. Door plugs are commonly used on commercial airframes,” wrote Bank of America analyst Ronald Epstein on Monday. He added that the issue could be an “assembly error” by Boeing, an “install error” by supplier Spirit AeroSystems, or an issue further down the supply chain.

The National Transportation Safety Board is investigating the cause of the accident onboard the Alaska flight Friday.

United is the largest operator of the 737-9 with 79 aircraft, followed by Alaska with 65 planes. Aeromexico and Copa Airlines are also affected.

The door plugs on the 737-9 are manufactured and installed by Spirit AeroSystems.