NTSB: All 12 stop fittings disengaged on Alaska plane door plug causing blowout

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Crookshanks added: “We have not yet recovered the four bolts that restrain it from its vertical movement and we have not yet determined if they existed there. That will be determined when we take the door plug to our lab in Washington DC.”

 

Given that the door plug has to move vertically to be released, there has to be space above the door to allow that movement. This space is clearly visible from the outside of the plane....

What is not clear (to me at least) is how is that space sealed airtight?
As for the missing bolts, cotter pin removal/failure plus unscrewing of the nuts* would have had to occur for all four bolts to have separated from the parts they were supposed to lock. That's statistically extremely unlikely.

Edit: * or fracture of the bolts

 

Given that the door plug has to move vertically to be released, there has to be space above the door to allow that movement. This space is clearly visible from the outside of the plane....
View attachment 312467
What is not clear (to me at least) is how is that space sealed airtight?
As for the missing bolts, cotter pin removal/failure plus unscrewing of the nuts would have had to occur for all four bolts to have separated from the parts they were supposed to lock. That's statistically extremely unlikely.

The plug can be opened to 15° to facilitate maintenance, so one possibility would be that it was opened, which requires removing the six bolts (four in the slots and two in the hinge posts) and they weren't put back after the plug was closed.

 

That's certainly one possibility, but since the plane was virtually new (~2 months old), would there have actually been any maintenance scheduled prior to the incident?

 

That's certainly one possibility, but since the plane was virtually new (~2 months old), would there have actually been any maintenance scheduled prior to the incident?

That I don't know. Depends on what kind of maintenance is done that required the plug to be opened. I've certainly seen aircraft that were designed such that things that normally wouldn't have to be touched for the life of the aircraft have to be painstakingly removed in order to perform maintenance that has to be done every month. But that doesn't explain those loose bolts that they've shown in those pictures since those are not the bolts that have to be removed to open the door. Those bolts may be unrelated to this incident, but are still indicative of a bigger, wider spread problem.

 

Those bolts may be unrelated to this incident, but are still indicative of a bigger, wider spread problem.

Yes, that is a concern.

 

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I've been asking myself the exact same thing:

Aviation experts raise questions about 737 Max ‘door plug’ design
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Historically, since we have had pressurized airplanes, emergency exits are designed to come inward… so why would they have not done the same thing with this plug?

 

I think maybe it’s all designed around seating capacity, sacrifice safety for additional space.

Or the engineer is narcissistic, unwilling to sacrifice his ego and put people at risk.

kv

 

I think maybe it’s all designed around seating capacity, sacrifice safety for additional space.

Or the engineer is narcissistic, unwilling to sacrifice his ego and put people at risk.

kv

Most likely the former ... with a smidgeon of the latter ...

 

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I've been asking myself the exact same thing:

Aviation experts raise questions about 737 Max ‘door plug’ design
View attachment 312475​

Root cause people.

That plug door design is not new and is perfectly safe if the bolts are actually in it.

“There really is not a big issue with having this door in there, if it was secured right,” Goglia said.

 

Root cause people.

That plug door design is not new and is perfectly safe if the bolts are actually in it.

Yes, of course the root cause always comes to people ... and still, I think an inward opening door (or plug, in this case) would've not only added valuable redundancy, but it would've (probably) been mechanically simpler and with fewer parts involved.

 

There's actually quite a few aircraft that have outward opening exits. I looked into this some time ago and discovered that there are more than I had thought. Many exits that appear to be outward opening initially open inward and then move so that they can open outward from that position. This is very common with main entry doors. Cargo doors usually open outward to maximize usable cargo space. Emergency exits seem to come in a mix. One concern with inward opening emergency exits, which are expected to be operated by passengers with lots of other passengers cramming behind them that all want to get out, is whether there will be the room necessary to open the door inward against a crush of possibly panicked passengers. There's a reason why fire exits almost universally open outward.

 

Root cause people.

I assert that quality would rise dramatically if they'd just eliminate Friday afternoons.

 

Yes, of course the root cause always comes to people ... and still, I think an inward opening door (or plug, in this case) would've not only added valuable redundancy, but it would've (probably) been mechanically simpler and with fewer parts involved.

That plug is designed to never open unless there is sizable maintenance action to the aircraft. As @WBahn as said there are safety advantages with an outward opening 'emergency' door but this was not a door.

 

That plug is designed to never open unless there is sizable maintenance action to the aircraft. As @WBahn as said there are safety advantages with an outward opening 'emergency' door but this was not a door.

No, it wasn't a door (it really wasn't a plug, either, but rather plug-like), but it had to be compatible with the emergency door system at that station.

 

I'm still puzzled by the visible gap above the door plug when the latter is correctly locked in place. Surely that is aerodynamically inefficient and will create turbulence?
Stuffing something in there would seal the gap, reduce turbulence and prevent the door plug inadvertently moving vertically. I think I'll suggest it to Boeing .

 

I'm still puzzled by the visible gap above the door plug when the latter is correctly locked in place. Surely that is aerodynamically inefficient and will create turbulence?
Stuffing something in there would seal the gap, reduce turbulence and prevent the door plug inadvertently moving vertically. I think I'll suggest it to Boeing .

I'm guessing you're joking.

The door needs to move physically up to unlock from the guides and be free of the holding flanges (the A320 does exactly the same thing, check the video) to hinge down or hinge to the side.

 

I'm still puzzled by the visible gap above the door plug when the latter is correctly locked in place. Surely that is aerodynamically inefficient and will create turbulence?
Stuffing something in there would seal the gap, reduce turbulence and prevent the door plug inadvertently moving vertically. I think I'll suggest it to Boeing .

Not much -- narrow slits that are aligned with the airflow produce only a small amount of drag. While it isn't zero, it has to be balanced against the fact that the emergency doors on aircraft that have them have to be able to move up and that the plug doors have to be compatible with them. Now, you could rig something that was, say, spring loaded and came down to fill the gap when the door was closed and that the door pushed up when it was opened, but that's added cost and weight, so will the marginally reduced drag provide sufficient savings over the ownership span of the carrier? I wouldn't be surprised if the numbers on that have been run.