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[Doctor Gollum]

First sensible take on it...

https://youtu.be/I9EvHpf8jZg?si=6Z63Mr_hwp6xTqfd

Looks like a derivative of the door used on the 757 for D3... That was also bottom hinged. Pulling the handle releases the clamps and it falls away from the aircraft deploying the slide as it goes. (All door mounted slides are clamped to the floor at the door frame when armed and this type would be permanently armed,
 very different to the equivalent door on an A321).

The obvious differences between this and the 757 D3 are a smaller bustle (shorter slide due to the much lower sill height) allowing for a standard window.

[Doctor Gollum]

And the ATC recording...

https://youtu.be/29ghXy6O2dc?si=r-8J41fFh1ox-qRw

[Doctor Gollum]

Check out playback of aircraft N704AL on Flightradar24. https://fr24.com/data/aircraft/n704al#3374f24e

And it spent New Years Day in the hangar.

[Doctor Gollum]

https://youtu.be/nw4eQGAmXQ0?si=UBSmTvKe8iW9Wjne

The missing piece and how it works.

[Doctor Gollum]

https://youtu.be/nw4eQGAmXQ0?si=UBSmTvKe8iW9Wjne

The missing piece and how it works.

And a bit more detail from the same source as to why it shouldn't just open...

https://youtu.be/maLBGFYl9_o?si=b834oc9QP7nCZ-fv

[TheBoy]

As I understand it, on the Max-9, this wasn't an exit, but had a special non functioning "door"?

[LC0112G]

It's an additional emergency exit that can be fitted to what is called 'high density' layouts - basically where the whole cabin is packed with as many seats will fit in the sardine can. Alaska Airlines don't do that - they have first class and buisness class, so the max number pf PAX on their B737-9's is only 170 odd. For that number of seats (up to 200 IIRC) the rules only require 8 emergency exits - which on a 737 are two front, two rear and 4 over-wing.

In their wisdom Boeing have fitted all Max-9s with provision for 10 exits - the additional ones are in the middle of the rear cabin each side - and if fitted and useable the aircraft can legally carry (IIRC) 239 PAX. However, in low density seating, this extra exit is sealed and blanked off, with all the hinges, handles and emergency slide stuff removed to save weight. Inside the cabin the passengers can't tell that the 'porthole' window they're looking through is any different from any other window, and there is no way for them to use this extra exit in an emergency.

So the question becomes how/why does a supposedly sealed emergency exit 'blow out'. Duff Boeing Design, Duff Boeing Manufacturing or Duff Alaska Airlines servicing would appear to be the obvious candidates.   

[Doctor Gollum]

As I understand it, on the Max-9, this wasn't an exit, but had a special non functioning "door"?

Essentially a blanking structure located and attached to the fuselage as  a door in the same position would have been.

On the Emergency Exit version the frame is beefed up to allow for the additional forces imposed buy the sprung loaded hinge and subsequent slide deployment and also to allow for the fitting of assist handles either side, but aside from a few extra.components this plug or door or plug door or door plug is essentially a door that can be opened using tools but serves limited purposes beyond maintenance access.

The basic latching and locating mechanism is the same for any door fitted in this position. The difference being that instead of cam locks it uses four wire locked through bolts to keep it in the latched and secured position. By virtue of how and where they are fitted, one such bolt would be sufficient...

So either someone screwed up in production or during the post delivery work at Alaskan... There's ten days clear between delivery and entry to service. Every aircraft regardless of manufacturer or customer arrives from the factory and goes into the hangar.

There's a whole list of stuff that has to be done from basic snagging and rectification to airline specific software/post production modification/fitting and checking safety equipment and markings etc.

And this aircraft was in the hangar overnight on January 1st. As bourne out by flightradar24.

[Doctor Gollum]

It's an additional emergency exit that can be fitted to what is called 'high density' layouts - basically where the whole cabin is packed with as many seats will fit in the sardine can. Alaska Airlines don't do that - they have first class and buisness class, so the max number pf PAX on their B737-9's is only 170 odd. For that number of seats (up to 200 IIRC) the rules only require 8 emergency exits - which on a 737 are two front, two rear and 4 over-wing.

In their wisdom Boeing have fitted all Max-9s with provision for 10 exits - the additional ones are in the middle of the rear cabin each side - and if fitted and useable the aircraft can legally carry (IIRC) 239 PAX. However, in low density seating, this extra exit is sealed and blanked off, with all the hinges, handles and emergency slide stuff removed to save weight. Inside the cabin the passengers can't tell that the 'porthole' window they're looking through is any different from any other window, and there is no way for them to use this extra exit in an emergency.

So the question becomes how/why does a supposedly sealed emergency exit 'blow out'. Duff Boeing Design, Duff Boeing Manufacturing or Duff Alaska Airlines servicing would appear to be the obvious candidates.

Regardless of the former, the latter is more likely.

From what I know of 737NG cabins, the FAA mandated inspection is probably a couple of hours work for both sides plus any rectification work. The side wall panel will pop off and everything you need to check is just there. Removing the seat would be an unnecessary complication.

And opening this 'door' has a maintenance function and you can't inspect the seals without opening it.

If you've not watched them, both of Chris Brady's videos cover it in much detail with clear pictures, although he does confuse up and down regarding how the door releases from the fuselage... It drops down behind the securing pegs and therefore has to go up to clear them in order to be opened. This is reiterated by the fact that the door has to go UP to clear the guide pins.

[Doctor Gollum]

If the bolts had been forgotten from the factory, the door would have opened at the first landing, equally it's unlikely that all four bolts failed simultaneously. Even if they were loose but otherwise correctly fastened, the door wouldn't be able to move.

[Doctor Gollum]

Well, Bob has found the door...

[Doctor Gollum]

https://youtu.be/WhfK9jlZK1o?si=2n46Q3NIJePlApKL

[Doctor Gollum]

https://www.youtube.com/live/kGWLBLb9Pm4?si=GGR84G4Lf__rbtOw

The latest NTSB press conference.

It turns out that the upper door guides sheared. On the face of it, this suggests that the upper bolts had been at least partially in place at the time as the path of least resistance would be to go UP and clear the guides. The fact that the guides sheared would indicate that the guide tracks are longer than the distance required to clear the stops, and for that failure to be the path of least resistance then the last remaining bolt must have worked loose and become jammed in the outer face of the guide rail as the door moved up and out. The spring pressure pushing the door up and the cabin pressure pushing the door out.

And for the springs to be able to push the door up, the bottom bolts were either missing or otherwise worked loose, the spring and pressure differential loads eventually overcoming the shear strength of the guides. When the door went it did so with enough force to rip both cable stays of the frame and force the lower hinge tubes past the stop washer on the end of the hinge posts.

What work either pre or post delivery had been carried out on that door will be a crucial detail. Interestingly no mention has been made of the last hangar input on January 1st.

Although, given that loose bolts have been found on other aircraft, it will be interesting to see what the fix is going to be.

[Varche]

I wonder if Ryanair will charge a premium for non window seats?

Pay £10 priority to guarantee you WON’T get allocated a seat next to an innocent looking window which is actually a “ plug” with loose bolts.

It is like something out of squid games!

[LC0112G]

The fact they seem to be finding the same/similar fault on some United Airlines planes suggests to me that it's not an Alaskan Airlines servicing issue.

The B737 fuselages are actually built by Spirit Aviation (in Witchita Kansas), and then moved by rail from Spirit to Boeings final assembly in Seattle. This is correct - they was a rail accident a few years ago where several fuselages were wrecked. One rumour going round is that in order to prevent dirt and grime getting into the airframe whilst in transit, Spirit fit the the main doors and door plugs. Once in Seattle the main doors and overwings are removed by Boeing for proper emergency exit fitting, but the plug doors are not. If Spirit only put the doors in 'loosly for transit' and don't fit them properly expecting Boeing to do that during assembly, then we have the required holes in the cheese.