Factory Error Could Have Led To Dangerous Door Plug Blowout On Boeing 737 Max

A door plug that blew out of Alaska Airlines Flight 1282Photo: National Transportation Safety Board (AP)

When a door plug blew out from an Alaska Airlines Boeing 737 Max 9 just minutes after taking off from Portland, Oregon, it raised several questions about the troubled airliner. Will airlines still be allowed to fly Boeing 737 Max 9? What the hell is a door plug? And how could it get blown out of the plane?

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First, the Federal Aviation Administration (FAA) requires that commercial aircraft include a minimum number of emergency exits based on the airliner’s passenger capacity. The regulations mandate that the Boeing 737 Max 9 have eight emergency exits because it can carry over 200 passengers. However, Alaska Airlines states that it flies the aircraft in a 178-seat configuration. What happens when an airline operates the 737 Max 9 in a configuration with less than 200 seats? Boeing can remove a pair of the exits.

This is where the door plug comes in. The plug does exactly what it says on the box: it fills in a hole in the fuselage where an emergency exit would have been. Using a plug over keeping the exit reduces complexity for carriers. No emergency exit also eliminates the need for an accompanying slide or life raft, lowering maintenance costs and the aircraft’s weight.

Photo: Craig Mitchelldyer (AP)

After an airline places an order for a six-exit Boeing 737 Max 9, the aircraft’s fuselage is built by Boeing’s supplier Spirit AeroSystems in Wichita, Kansas. The fuselage is then shipped by train to Boeing’s factory in Renton, Washington with the plug already in place. According to Reuters, the plug isn’t fully fixed before the transfer. Boeing will remove the plug to make accessing the interior easier and reinstall the plug before delivery.

With the National Transportation Safety Board investigation still ongoing, it’s not known exactly how the door plug blew out on Alaska Airlines Flight 1282. However, early details point to it being a manufacturing issue. Alaska Airlines and United Airlines found loose bolts on other relatively new Boeing 737 Max 9 aircraft. Boeing likely delivered the planes with bolts that were not properly fastened.

The FAA temporarily grounded Boeing 737 Max 9 planes until they undergo inspection. Similar to the ongoing order after a nut was found to be missing on the rudder control linkage on multiple 737 Max planes. Beyond the loose bolts, door plugs aren’t doors. They don’t have to open. An exit door plug is supposed to be wedge-shaped. If there is a bolt issue, the plug should be pinned to the fuselage opening and not fly clear of the plane.