Boeing: Profits 1st, Safety 2nd? (Part 3)

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Message 2132558 - Posted: 14 Feb 2024, 18:05:06 UTC - in response to Message 2132510.  
Last modified: 14 Feb 2024, 18:26:39 UTC

Does a blown out door plug actually have the potential to lead to a total disaster, such as tearing the airframe apart due to sudden decompression?

Very definitely yes. You're into not-designed-for uncharted conditions...

Note that under normal pressurisation, there is 1000's lbs/kg of pressure pushing inside to outwards on just the door alone...

So... After great luck that the ripped-off door didn't snag the skin of the fuselage, or bounce alongside in the turbulence, there's further risk of total loss if it were to hit the tailplane...

The door fittings are fixed directly to the aircraft ribs. We can hope that the bolts and fittings have deliberately been designed to be sacrificial and to break before doing further damage... Or have they?...

Can the aircraft ribs survive if the door had failed on the leading side first, to then be violently twisted out of the frame? Has that deliberately been designed for?...

But now... You have a very sudden very significant unloading on one section of the pressure cylinder... Has that deliberately been designed for??

And then after all that, you're relying on nothing further untoward happening for some very uncomfortable and stressed pilots in the sudden cold and harshly noisy cockpit conditions from the ferocious outrush of air. Such a depressurisation can cause temporary or even permanent loss of hearing. All immediately followed up with a cacophony of alarms... And just the 1960's Boeing one angry blinking indicator light to unhelpfully indicate "something" has gone wrong...


All very 'difficult' and all too very ready to go very wrong.

Another "fortuitous" detail is that the door happened to be behind the engine, and so didn't catastrophically destroy an engine... And that the emergency slide ripped off in such a way to so as not drag along, or to wrap itself around the tailplane or rudder...


There's a scary litany of lucky fortuitous good fortune for a less serious outcome for that day...

All on a wing and a hundred prayers...

Fly safe?
Martin
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Message 2132566 - Posted: 14 Feb 2024, 19:48:43 UTC - in response to Message 2132558.  

And that the emergency slide ripped off
Where do you get this fiction? What emergency slide?
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Message 2132569 - Posted: 14 Feb 2024, 20:33:23 UTC - in response to Message 2132566.  

As the NTSB preliminary report does not mention the loss of an emergency slide then it is fairly safe to say that there was no emergency slide fitted to that doorway. Remember that these preliminary reports summarise the damage to the aircraft concerned and its equipment (presence or absence). What appears to be happening is people are seeing the damage to the lower retaining straps, and assume that there was an emergency slide in place. There may be the "box" that would normally hold the slide, but that isn't mentioned so it either wasn't specified or wasn't damaged.
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Message 2132572 - Posted: 14 Feb 2024, 21:38:05 UTC - in response to Message 2132558.  

Note that under normal pressurisation, there is 1000's lbs/kg of pressure pushing inside to outwards on just the door alone...
1000's of lbs or kilograms???? This high pressurization forces? Let's have a rough estimate:

Air pressure (ignoring temperatures):

  • at sea level: 1,013.25 hPa
  • at 2,500 m / 8,200 ft (cabin level): ~747 hPa
  • at 5,000 m / 16,400 ft (roughly the level of AS1282's door blowout): ~540 hPa
  • at 11,000 m / 36,000 ft (cruise level): ~226 hPa


So the pressure difference from cruise level to cabin level is:

747 hPa - 226 hPa = 521 hPa = 52,100 Pa = 52.1 kN/m² = 5,210 kg/m² = 123,634 lbs/sqft

...and from accident level to cabin level:
747 hPa - 540 hPa = 207 hPa = 20,700 Pa = 20.7 kN/m² = 2,070 kg/m² = 49,121 lbs/sqft

A Boeing 737 door spans.... maybe 2 square meters = ~21.5 sqft

That's a force corresponding to 10.4 metric tons or 11.5 short tons pushing against the door plug at cruise level.

The Alaska 737 Max 9 lost its door plug at ~16,000 ft. At 16,400 ft a force corresponding to 4.1 metric tons or 4.5 short tons pushed the door plug out. Wow.

I never thought about the true numbers related to pressurized airframes. After all it's air not water. It's obvious that submarines are exposed to high pressure changes, therefore large forces. I wasn't aware that forces on pressurized airframes are this large.

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Message 2132578 - Posted: 14 Feb 2024, 22:27:09 UTC - in response to Message 2132572.  

The plug closes what can be configured as an emergency exit, which are somewhat smaller than the normal entrance doors, but your logic is solid - it's a frightening amount of force acting on the plug, measured in ton(ne)s.
Blancolirio does the sums at about 11:30 in this video https://www.youtube.com/watch?v=fnFzT6aUehg.
(One has to excuse his helmet fire - he's an airline pilot with many years of experience, and, like those of us who "fly at the back", he always wants to get home from work to see his family.)
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Message 2132579 - Posted: 14 Feb 2024, 22:37:48 UTC - in response to Message 2132578.  

This is a classic case where "failsafe design" would have prevented the near-disaster. If the plug had been designed to be fitted from the inside, all that pressure would have simply seated it more firmly in its seating. The bolts would have been a secondary restriction of movement, not the primary line of safety.
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Message 2132582 - Posted: 14 Feb 2024, 23:57:01 UTC - in response to Message 2132579.  

... And this is another Boeing 'classic case' of 'would have'...

Why such a compromise in the first place?

And how was that allowed??


Really fly safe???
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Message 2132583 - Posted: 14 Feb 2024, 23:59:09 UTC

Slight tangent:

Whatever is happening to the latest "Test Flight" of the Boeing Starliner?...

That has curiously not been in the news for a while. And there is no mention of it flying?...


Fly safe?
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Message 2132586 - Posted: 15 Feb 2024, 2:12:58 UTC

All those numbers, remember there are 10 total door holes on that air frame.

As to this rip apart, Aloha Airlines flight 243 shows just how strong those bulkheads are. Boeing 737-200 btw.
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Message 2132613 - Posted: 15 Feb 2024, 12:54:40 UTC - in response to Message 2132572.  
Last modified: 15 Feb 2024, 12:56:12 UTC

So the pressure difference from cruise level to cabin level is:

747 hPa - 226 hPa = 521 hPa = 52,100 Pa = 52.1 kN/m² = 5,210 kg/m² = 123,634 lbs/sqft

...and from accident level to cabin level:
747 hPa - 540 hPa = 207 hPa = 20,700 Pa = 20.7 kN/m² = 2,070 kg/m² = 49,121 lbs/sqft

  • 5,210 kg/m² = 1,067 lbs/sqft
  • 2,070 kg/m² = 424 lbs/sqft


Uuh, reminds me of: There are two types of countries in the world: those that use the metric system, and those that have put a man on the moon. I think, I disqualified myself. :-(

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Message 2132614 - Posted: 15 Feb 2024, 13:18:29 UTC - in response to Message 2132586.  

All those numbers, remember there are 10 total door holes on that air frame.

As to this rip apart, Aloha Airlines flight 243 shows just how strong those bulkheads are. Boeing 737-200 btw.

You still want to take your chances that nothing else fails??

Or do you enjoy that extra 'thrill' of flying with randomly loose and missing bolts?...


Also note that a door blow-out can destroy the aircraft and all those on board:

cargo-door blowout caused Turkish Airlines Flight 981 to crash


That's no minor matter...

Fly safe?
Martin
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Message 2132623 - Posted: 15 Feb 2024, 15:53:28 UTC - in response to Message 2132614.  

Also note that a door blow-out can destroy the aircraft and all those on board:

cargo-door blowout caused Turkish Airlines Flight 981 to crash
The strange thing is: aircraft doors are very heavy, thick, massive construction parts that have a complicated mechanics to first move them a little inwards into the airframe, to then swing them out (fail-safe design). Cargo doors, on the other hand, appear to be very lightweight structures that simply open outwards. A simple lever mechanism locks it. This difference seems strange since both decks are part of the same pressurized airframe.
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Message 2132626 - Posted: 15 Feb 2024, 16:35:36 UTC - in response to Message 2132623.  

Passenger door appear to be very thick and heavy, but in reality they are a thin skin with a lot of "padding" on the inside - weight they are pretty light for their size and the complexity of their hinges, locks etc. The skin is about the same as that of a cargo door, but the fixes and fittings are hidden on the passenger door, but often exposed on a cargo door.
(Both doors open by an initial "inward" motion, followed by an outward rotation.)
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Message 2132627 - Posted: 15 Feb 2024, 16:42:57 UTC - in response to Message 2132579.  

The both doors and plugs, in their closed & secured position, are fitted from the inside. But may appear to be closed from the outside (some really strange mechanisms in play to get it all to work.....).
The basic design for securing plug has been used on a good many types of aircraft for a good few years, I think their first use was on certain b373-200, and this is the first time (to my knowledge) that one has failed. That said, to me, it does look to be a very fragile system, relying on a number of small pads to prevent the door/plug from popping out, an small pads means a small movement is required for the thing being secured to pop out and depart the aircraft.
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Message 2132629 - Posted: 15 Feb 2024, 18:42:04 UTC - in response to Message 2132627.  

What being missed by most is those pads have a recess in the center where a pin from the other side to engage. So yes the plug has to move inward a tad before it can move up and then go out.

There is a photo in the report of one of the pads and it appears as if the plug was never closed completely never mind the bolts being missing. Which would have made putting the bolts in impossible. One wonders, huh they don't fit, must not be important droid worker ...
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Message 2132635 - Posted: 15 Feb 2024, 22:50:30 UTC - in response to Message 2132629.  

Figure 14 of the NTSB preliminary report shows the plug to be sitting correctly on the pads, and the four bolts missing.
I think you are talking about figure 9 in the report which is a post incident "reassembly" of one of the pads against its opposite number on the door, this photo is there to show how the damage on the pad and the plug line up, this is clearly not how it was in service as the pad has been removed from the airframe.

NTSB Interim report
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Message 2132639 - Posted: 16 Feb 2024, 1:33:34 UTC - in response to Message 2132635.  

Figure 14 of the NTSB preliminary report shows the plug to be sitting correctly on the pads, and the four bolts missing.
I think you are talking about figure 9 in the report which is a post incident "reassembly" of one of the pads against its opposite number on the door, this photo is there to show how the damage on the pad and the plug line up, this is clearly not how it was in service as the pad has been removed from the airframe.
Correct #9, the damage does not look to be scrape as opening under pressure, but more like many cycles of misalignment. As to #14 I'm not going to say what may or may not have moved when they stuffed all the insulation, vapor barrier and the like back into place before putting the cosmetic interior plastic back. However I'm sure the final report with microscopic, dye and x-ray may show force direction and or repetitive cycles better than the preliminary. All of which is interesting but if you put the bolts in never needed.
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Message 2132658 - Posted: 16 Feb 2024, 18:58:45 UTC
Last modified: 16 Feb 2024, 19:23:07 UTC

I an surprised activists have not sued for the devaliuation of the brand because of the safety issues.
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Message 2132728 - Posted: 18 Feb 2024, 19:28:04 UTC

Boeing gets a special mention, TWICE over, in this Space News:


Stephen Colbert - Space News


That's a very deadly Ouch!

No laughing matter??...


Fly safe?...
Martin
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Message 2132747 - Posted: 19 Feb 2024, 0:20:30 UTC - in response to Message 2132728.  

Stephen Colbert is always a laughing matter.
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Message boards : Politics : Boeing: Profits 1st, Safety 2nd? (Part 3)


 
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