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khenleydia
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Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 3:11 am

I recently read an article that was talking about problem with the flight-deck doors and their locking mechanisms. While reading this article, one thing caught my attention. It stated that the doors need to be secured BUT be able to fly open in the event of an decompression. I believe they mentioned it as an "Explosive" Decompression.

Now, I understand the problems with decompressions, but I must say, I am a bit surprised and baffled by the need for the door to be able to open in those cases. Simple question... Why?

Second question, was there an event early in pressurized flight history that made them discover the need for this?

Thanks!

KhenleyDIA
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FredT
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 3:18 am

As it would put a load on the aircraft it is not designed for to have the cockpit pressurized while the cabin is not pressurized. Calculate the forces on the structures separating the cabin from the cockpit with the correct pressure differential. They are very significant. You really don't want the avionics rack and the forward lavatory come shooting into the cabin as the cork out of a champagne bottle.

To enable one compartment to be pressurized but the other not, you would need a pressure bulkhead between the compartments. This is clearly not desirable for a multitude of reasons, and all but impossible to retrofit.

Thus, blowout panels if the door cannot be designed to open due to perceived security reasons. Kneejerk reactions galore... but that's another debate.

Cheers,
Fred
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TimT
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 3:23 am

Flight deck doors, while providing security for the crew are still open to the rest of the aircraft thru a vent panel system. There are sliding panels built into the door that allow for pressure to equalize on both sides. When closed and secured from the cockpit, the only way for the door to "fly" open would be a deformation of the airframe. At any rate, the structure around the door and the aft wall of the cockpit is not sealed to the point the pressure would cause any problems. And I'm not sure, but I think there's something in the requirements about the crew having an escape route other than the windows in the event they need it. Such as kicking out the panels and crawling thru the door.
 
khenleydia
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 3:52 am

Quoting FredT (Reply 1):
You really don't want the avionics rack and the forward lavatory come shooting into the cabin as the cork out of a champagne bottle.

No, you wouldn't really want that. I figured though, that the flight-decks were more like what TimT mentioned. They can equalize to the cabin pressure, but through another "vent" or something like that. Maybe even drop to a certain level, but then slow the equalization. Since the pilots don't fly wearing their O2 masks, even if it was able to stay more "pressurized" then the rest of the cabin, a bit longer to give them time to get on air.

There is a reason why I don't design planes. I just enjoy learning about them a lot!  Smile

Thanks.

KhenleyDIA
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SlamClick
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 4:02 am

Common sense would dictate that in future designs the blowout feature be built into the bulkhead and not the door, and in such a way that a person could not pass through the opening.
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MD11Engineer
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 4:10 am

The planes I currently work on have two blow out panels in the door, which are secured by latches, which open if there is a pressure differential. You can not kick them in, but a simple aneroid mechanism in each latch will let the panels drop out if there is a pressure differential.

Jan
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barney captain
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 4:15 am

Quoting FredT (Reply 1):
You really don't want the avionics rack and the forward lavatory come shooting into the cabin as the cork out of a champagne bottle.

Except those panels are only designed to blow in, not out. The idea is to allow cabin pressure to rush forward in th event of a sudden decompression in the cockpit, thereby giving the crew extra time to don o2 masks.
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widebody
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 8:18 am

Depends on which aircraft type you're on about, different aircraft have different designs. On the Airbus fleet, the door opens inwards on all aircraft in the case of a cockpit decompression (most critical because of the small volume). On the A330/A340/A300/A310 fleet, there is a panel in the door that opens into the cabin to equalise pressure in the case of cabin decompression. On 737, there are 2 panels in the door that open into the cockpit (i.e. the door doesn't need to open).

As for the need, depends on where the hole opens up and how large it is. As in any decompression, there is a sudden peak followed by a kind of exponential tailout. In each case, the size of the peak is compared to the design structural loads to see where does the peak fall. If the peak reaches the limits of the structural load, you need to open open 'area' somewhere to reduce the size of the peak. This is what the various doors/hatches/panels do - open up venting area to prevent the hole creating a pressure peak that is beyond structural loads.
 
474218
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RE: Flight-deck Doors And Decompression...

Mon Oct 10, 2005 1:06 pm

Why would blowout panels be needed on the flight station door (to equalize pressure) when there are no blowout panels on the lavatory doors? The area between the forward pressure and the aft pressure bulkheads is all pressurized at the same time. That includes flight station, the main cabin, and the cargo compartments. If there is decompression it happens almost instantly throughout the entire pressurized area. The flight station is not sealed off from the rest of the pressurized area. The flight station bulkhead is not a pressure holding bulkhead is it?

[Edited 2005-10-10 06:09:45]
 
bri2k1
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 1:43 pm

Quoting SlamClick (Reply 4):

It's been argued that the easiest way to prevent terrorists from hijacking an airplane is to physically segregate the cockpit from the cabin. The pilots would enter through a seperate exterior door, which would obviously be unreachable during flight. The only thing the terrorists could do is blow the plane up, it could never be made to fly to a different destination. The only problem is if both pilots died. As another thread has tried desperately to prove, there wouldn't be any hope in that situation anyway, so why bother?
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HAWK21M
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 3:00 pm

Any pics of the Cockpit doors post 9/11 with Blowout panels Depicted.
regds
MEL
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ha763
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 5:37 pm

Quoting 474218 (Reply 8):
Why would blowout panels be needed on the flight station door (to equalize pressure) when there are no blowout panels on the lavatory doors?

Because the reinforced cockpit door could cause a lot more damage if pressure could not equalize. The lav doors are not very strong and probably would not cause any damage.

Quoting HAWK21M (Reply 10):
Any pics of the Cockpit doors post 9/11 with Blowout panels Depicted.

This is the prototype door Boeing was showing airlines for the 747, 767, and 777. I haven't seen the actual production door, but was told by the guys from Boeing who demonstrated the door that this was basically the design. The controls on the black pedestal are the controls to open the door from the cockpit, which IIRC, were supposed to located in white area depicted on the diagram of the overhead panel shown on the wall. Oh, the blowout panels are the gated areas on the top and bottom of the door.

 
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HAWK21M
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 10:01 pm

Would an Impact on the Blowout panel from Inside open the Panels.Just a query.
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MEL
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widebody
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 11:04 pm

Depends, on Airbus types the door also acts as an emergency escape route for the flight crew. Pins have to be removed on A320F before the panel can be pushed out, on A330/A340/A300/A310 a device is installed that will automatically retract the pins when pressed to allow the panel to be pushed into the cabin.
 
Tod
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 11:33 pm

Quoting KhenleyDIA (Reply 3):
Since the pilots don't fly wearing their O2 masks, even if it was able to stay more "pressurized" then the rest of the cabin, a bit longer to give them time to get on air.

The blowout panels only exist to address structural loads during a rapid decompression event.

Quoting 474218 (Reply 8):
there are no blowout panels on the lavatory doors?

The thinking was that a lav is an enclosed box, not exposed to rapid decompression from within, but now that some lavs have windows, I don't know and I'll have to ask a DER with decompression approval authorization.
Sometimes the status quo is accepted until the issue is raised.

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widebody
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RE: Flight-deck Doors And Decompressions...

Mon Oct 10, 2005 11:46 pm

Because the lavatory isn't part of the structure, therefore whether it or its walls survive a decompression event or not won't have an impact on the aircraft structure. Same for overhead bins, storages etc - these have no panels either. Blowout panels and such devices are only required where flow within compartments of the pressurised structure can be too slow to prevent pressure peaks e.g. on many aircraft types, if the flow from cabin to cockpit is impeded, it's the floor which will give way as its the next weakest area (all other surfaces are primary structure).

[Edited 2005-10-10 16:49:12]
 
FredT
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RE: Flight-deck Doors And Decompressions...

Fri Oct 14, 2005 2:16 am

Quoting Barney Captain (Reply 6):
Except those panels are only designed to blow in, not out. The idea is to allow cabin pressure to rush forward in th event of a sudden decompression in the cockpit, thereby giving the crew extra time to don o2 masks.

That's a negative. The idea is, as I said and others as well, to save the structure between the two compartments if one depressurizes. If the blowouts only go in, you are likely to find that in case of a decompressed cabin the door itself is designed to come ajar enough to let the air out of the cockpit.

I reiterate: If it was intended to keep pressure in, it would be a pressure bulkhead. Simple as that.

Quoting 474218 (Reply 8):
Why would blowout panels be needed on the flight station door (to equalize pressure) when there are no blowout panels on the lavatory doors?

If the cabin decompresses, the lav doors will come flying out of the lavs. They are not strong enough to resist the pressure difference, just as many older cockpit doors which didn't need blowouts. If the lav decompresses, the door will probably collapse into the lav. Not pleasant if you happen to be in there, but it shouldn't be life-threatening either.
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Starlionblue
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RE: Flight-deck Doors And Decompressions...

Fri Oct 14, 2005 3:57 am

Quoting FredT (Reply 16):
If the lav decompresses, the door will probably collapse into the lav. Not pleasant if you happen to be in there, but it shouldn't be life-threatening either.

This paints a lovely picture Big grin
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MxCtrlr
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RE: Flight-deck Doors And Decompressions...

Fri Oct 14, 2005 3:58 pm

The blowout panels are designed to deploy if the cockpit pressure is less than the cabin. The idea is to keep flying doors out of the cockpit and off the pedestal. If the cockpit door needs to fall into the entryway, nobody cares.
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RedDragon
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RE: Flight-deck Doors And Decompressions...

Sat Oct 22, 2005 9:53 pm

Quoting FredT (Reply 16):
If the cabin decompresses, the lav doors will come flying out of the lavs.

As in, they'll come off their hinges? Wouldn't this pose a bit of an injury risk for passengers and crew seated nearby?

Rich
 
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HAWK21M
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RE: Flight-deck Doors And Decompressions...

Sat Oct 22, 2005 11:32 pm

Quoting RedDragon (Reply 19):
Wouldn't this pose a bit of an injury risk for passengers and crew seated nearby?

The Door Location will probably Eliminate that.
regds
MEL
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SATL382G
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RE: Flight-deck Doors And Decompressions...

Sun Oct 23, 2005 4:48 am

Quoting FredT (Reply 16):
If the cabin decompresses, the lav doors will come flying out of the lavs.

I doubt there is enough volume in the lav to cause the doors that much distress.
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