Alaska Airlines flight forced to make an emergency landing... 82

[jrs87]

View of hinges. Due to minimal damage, it seems the door simply transitioned upwards and then opened.

https://www.flickr.com/photos/ntsb/53450362798/in/album-72177720313904488/

Loose bolt visible:

 

[jrs87]

 

[Murph 9000]

That's not one of the bolts that holds the plug in place when it's closed. That's the top of the tubular section that extends out from the hinge, with the green collar around it that should be attached to the plug (and was presumably torn off by the forces presented by the airflow when the plug popped open in flight). The bolt which prevents the plug opening would have gone through a radial hole in that collar and the tubular section of the hinge. The visible nut and washer there, as far as I can tell, is just to retain the plug on the tubular hinge section when it's fully open (otherwise it would just slide off).

There's a bit of a mystery around the "loose bolts" that keep being mentioned. Just being loose would not have allowed this incident to occur, they have to be completely missing/removed to allow the plug to move upwards and disengage the stop fittings/pads. If they are loose, but still in their correct bolt holes and have the cotter pin correctly in place, they should still function adequately to prevent the plug from opening. It's not clear exactly what is being communicated by the mention of loose bolts being found on other MAX 9s. It's probably not desirable to have them too loose, but shouldn't be imminently catastrophic; the plug does not depend on them being tight to keep it in place.

Edit: That's for the 4 bolts involved in opening and closing the plug, and the nut on the end of the tubular hinge extension. Obviously there are other bolts around, possibly related to the plug and frame, which could be critical if insufficiently torqued.

 

[dik]

Thanks murph...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[jrs87]

Loose bolt talk

You are mostly correct Murph. No bolts keep the plug closed. The pads do not keep the plug closed, they act in the other direction and absorb negative pressure and minor distortion. The plug is held in place by the interference with the frame when in the lower position or perhaps by the roller pin and lower hinges. Two bolts in the pin/catch keep the plug on the track. The mystery is if those bolts went missing and how did the door move up against the force of air pressure? The roller pin and hinges are intact. The bolt in the photo seems completely backed-out, but perhaps the NTSB removed a dangling part and did this.

 

[3DDave]

There seems to be a circulation of loose and missing hardware in the news.

1) In the rudder control system, which disables pilot inputs, but not the automation input to control yaw stability.
2) Highly suspected in the departure of the door
3) In checking to see that all door hardware is in place, fasteners intended to hold portions of the door brackets to the door have been found unsecured.

The main communication seems to be that there are gaps in the Boeing final assembly area when it comes to ensuring that hardware is where it is supposed to be.

For all I know this is common at all aircraft makers, but the door departure with instant coverage and plenty of people to interview has drawn more attention to it than any of the other 10,000 other manufacturing problems that have made their way into products with some having fatal results.

If I were CEO of Boeing I would be on the factory floor yesterday asking a lot of questions. Were it just one door, sure, bad day. But finding other fasteners loose while inspecting the doors? That's at least a chain 3 deep of QA and QC and manufacturing engineering likely to get fired unless they can demonstrate sabotage has taken place.

 

[jrs87]

https://www.reuters.com/business/ae...-part-boeing-has-key-role-sources-2024-01-07/

Quality control is more difficult when more than one factory floor is involved. (Not clear if MAX 9 is shipped by rail.)

 

[EdStainless]

And now I am reading that both Alaska and United have found loose retention bolts as they have started inspections.
These bolts are installed at Spirit.
It will be interesting to see what they find in unbuilt and unshipped hulls.

The only flight that I ever skipped because of the plane was a flight in China on a Russian plane.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Murph 9000]

The pads do not keep the plug closed, they act in the other direction and absorb negative pressure and minor distortion.

No, the stop pads very much do absorb positive cabin pressure (i.e. the normal case in flight). The "stop pads" on the frame are outboard, and the "stop fittings" on the plug are inboard when the plug is in the fully closed position, transmitting positive cabin pressure into the frame via the pads. The 4 bolts (2 through the guide fittings, blocking the pin; and 2 through the collar and tubular hinge extension) prevent the door sliding up vertically and disengaging the stop pads and fittings. The plug has to take a positive pressure delta of around 8 psi, and only around negative 0.5 psi (I'm not sure if those are the exact numbers for the MAX, but they should be a rough approximation).

The guide/roller pins and hinges are not really part of handling the positive pressure, although they might be what handles negative pressure.

 

[jrs87]

Stop pads

Thank you for the clarification. Very much appreciated. It seems the inflight pressure on the pads would keep the door plug in place unless the plug was partly open before pressurization.

 

[waross]

These bolts are installed at Spirit.

There have been strong suggestions that the bolts may have been removed and the plugs opened at the Boing plant.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Murph 9000]

It's certainly been suggested that these doors may have been used for getting things in and out of the cabin during fit out, which could even include the airlines, if they made any changes after delivery.

 

[LionelHutz]

I'm guessing that the loose bolts that were found by United are the bolts holding the door/plug lower hinge piece onto the door/plug frame. The part that slides up and down on the hinge tube. The upper bolts retaining the plug in position should still hold the plug in place if this was that case. That might be why the upper pin was found damaged.

 

[waross]

The door must move upwards so that the side pins may clear the stop pads.
There is over-travel on the top guide to allow clearance tolerance so that the stop pins may safely clear the stop pads before dropping in behind the stop pads.
As the door crept upwards, as soon as the stop pins were clear of the stop pads, the door departed.
Th door had not yet lifted far enough for the guide pins to clear the guides so that the guides were damaged.
Four bolts is nice symmetry, but even one bolt should have prevented the door from moving upwards.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[JohnRBaker]

While this has nothing to do with the door itself, other than it ending-up where it did because of the failure, an Apple iPhone was found which appears to have fallen from the plane and not only did it appear to be undamaged, is was still fully functional (this would be a great opportunity for an Apple advert).

Passenger phone found on ground after Alaska Airlines emergency

https://abcnews.go.com/US/passenger...-alaska-airlines-emergency/story?id=106186623

And yes, the phone was in 'Airplane Mode' when it was found ;-)

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[Tomfh]

What sort of bolts are they? How do they work? What does “loose” mean?

 

[3DDave]

There is a bracket that goes between hinge and the frame of the door that has what appears to be 4 fasteners. It slides on the hinge guide. At least 3 visible bolts were clearly loose in that joint.

 

[SWComposites]

“Loose” means not torqued to spec.
Std aerospace bolts, probably Titanium, possibly CRES.
The loose bolts seem to be on the door structure, not 4 used to prevent the door from moving upwards, which must happen to allow the stop pads to clear and allow outward movement.
Loose bolts still not good, as could lead to fatigue failure.
The stop pads are not “flimsy”. We don’t put extra weight into the structure beyond what is required.

 

[SWComposites]

And fuselages, with the doors installed, are statically tested to 2X max design pressure.

 

[enginesrus]

Search Blancolirio on youtube, he is an airline pilot and is the best for explaining anything aircraft accident related.

In one of the photos in this thread, there is one bolt at the bottom of the fitting that does not look tight.

It was the lack of cabin pressure that allowed the door to become disengaged with the lugs, and not being secured would have moved out of position and off it goes.
Be happy there was not a child seated next to it. There should be no seats next to a plug door, and that weight savings can be put into some stronger materials where needed.

No matter what I would still question material choices for what all those poorly attached fittings are attached to, just looks like a problem waiting to happen.