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Comment by akira2501 | Hacker News Reader

> these false door panels are not.

It's not a control surface, but it is a "moving part." That's what's baffling to me, that they spent a lot of effort building this hinge and pin roller system, and designed the door to hinge open up to 15 degrees.

It makes me wonder if there's maintenance procedures that at some point would require the operation of that door to successfully complete. Otherwise, the mechanism itself seems so incredibly overwrought, with lots of additional bolts, castle nuts, retaining pins, and even sprung hinges at the bottom.

Does anyone know why this "plug-type non-plug door" is built this way?

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It's built to be an actual emergency exit.

It needs to be usable depending on how many passengers the interior is configured for.

So it has all of the door bits there. Maybe some parts like the emergency escape slide are not installed.

e: I should be clear that it's not usable as an emergency exit, as configured by Alaska. However the operator could choose to activate it later and install a usable exit.

This is not correct. To the passengers, this just looks like another seat next to a window with a plug installed. It's not a door.

If there was a reconfiguration to a seating standard that required the extra exit, the plug would be removed and a proper door would be installed, with the associated interior pieces.

> To the passengers, this just looks like another seat next to a window with a plug installed. It's not a door.

This is true.

However there's still common hardware in there to allow the plug to be installed and maintained. This is why it's a complicated set of kit vs just bolting in a permanent fixture.

Where did you see that? My understanding is that it's an optional plug door that's used to assist with interior installation. Once the interior is done, it's bolted shut and interior paneling is installed over top. From the inside, you can't tell it's there.

My source is [1], specifically at about 5:05.

Alaskan airlines chose a 178 passenger configuration for their 737-9, and so are not required to have a mid-cabin exit door.

Lion Air's chosen to go with a 221 passenger configuration, and so are required to have an operating door.

Obviously changing up the number of seats isn't done on-demand, you'd need to go for a refit/maintenance cycles.

But if Alaskan decided to change density, or sold the aircraft to someone else who decided to change density - then they could go and do this.

[1] https://youtu.be/nw4eQGAmXQ0?t=305 "The Boeing 737 Technical Channel"

Ahh. Well, in the case of the Alaska flight, it's a plug door and not used as an exit. It's pinned in place with large pin that has a bolt, a castle nut and cotter pin which lock the pin.

> It's built to be an actual emergency exit.

If you are correct, then the implication is that the concern extends beyond door plugs for MAX-9 737s to all emergency exit doors on all models of aircraft sharing this design. This is somewhat reminiscent of the huge problem with the 688 (Los Angeles) class submarines, where the discovery of a faulty weld that had passed inspections raised doubts about all welds.

This is not true. It's designed to be opened when inspecting the fuselage for corrosion or stress cracks at the opening. To open it you have to remove the interior plastic panels and undo the 4 bolts that this accident is about

my guess is: to replace gaskets/seals

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