January 11th 2024
On January 5th Alaska Airlines flight 1282 departed Portland International Airport and on climbout around 14,000 feet the left side plug door departed the aircraft, causing a rapid depressurization. The climb continued to approximately 16,000 feet before the crew started a descent to 10,000 feet and then shortly thereafter completed an approach back to Portland.
This plug door is in place for operators who use a high density layout where the additional number of passengers need an additional emergency exit. At Alaska Air, and for many other airlines, including all US operators, this door is not required as an emergency exit so a plug door is installed and, from the inside of the aircraft there is no indication that there is a door.
There are plenty of other articles on how the this plug door works, but in essence in normal operation the door is held in place by the pressure inside the aircraft pushing the door outwards and 12 lugs on the door and the frame connect and hold the door in place. When the plane is pressurized there are no bolts that specifically hold the door in place. However, this plug door can be opened for maintenance and in order to open the door it must be lifted up approx one and a half inches so that the 12 lugs no longer line up and the door can fall outwards (prevented by straps from opening more than a few inches). In order to stop the door lifting there are 4 bolts. At the bottom of the door are 2 hinges that have a spring loaded mechanism to assist in door opening. These hinges are prevented from lifting by 2 bolts through each leg. At the top of the door is a large pin and a track that the pin rides in that when fully engaged places the door in the operational position. There are 2 bolts installed in the track, below the pin, that prevent the door from lifting. None of these 4 bolts hold the door closed, they just prevent the door from rising and the 12 pressure lugs from disengaging.
At their last briefing the National Transportation Safety Board (NTSB) (somewhat recklessly in my opinion) suggested that the 4 bolts holding the door from rising were perhaps not in place. Certainly that could have been the case, but it assumes that the friction of the pressure lugs when not under pressure was sufficient to override the hinge spring uplift assist for 2 months – and that seems unlikely. But the idea is that turbulence could bump the door up leading to the pressure lugs no longer being aligned and the door departing.
An alternative theory is that the bolts were installed but were not “tight”. The bolts are secured with a castellated nut and a pin that goes through the bolt and that prevents the nut from backing off the nut. So under this theory none of the pins in the bolts would have been installed and none of the bolts were tightened and then the nuts worked themselves off, and the bolts worked themselves out of the holes and then we’ve reached the position similar to if the bolts hadn’t been installed at all. My opinion is that only one bolt in place would hold the door from rising, and there is no particular excess stress on a single bolt than there would be if all 4 bolts were installed. So it would take a long series of failures for this theory to be the actual issue.
There are now pictures circulating that purport to show loose bolts in the area that holds the hinge mounting brackets for the lower part of the door. However, even if both hinge mounting brackets were loose, and essentially the entire bottom of the door was free floating, the tracks, pins and bolts at the top of the door would prevent the door from rising, and so the 12 pressure lugs would remain aligned. The hinges do not hold the door closed under pressure, they are just 2 points out of 4 that prevent the door from rising, and the remaining 2 points should be sufficient to hold the door in place.
So while it is incredibly hard to believe the idea that the bolts were never there in all 4 locations this does seem the most likely option, since the idea that all the bolts were misinstalled and all backed out in 2 months just seems difficult to believe. Somehow friction held the door in place for 2 months and one particular bump caused the door to lift and subsequently depart.
The NTSB will figure it out – they can analyze the various pieces and holes and determine if the bolts were installed and if they were what happened to them or if there was some other failure that led to the departure of this door.
