julesmusician
Posts: 378
Joined: Sun Aug 28, 2005 3:25 am

Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 6:57 am

I have heard that a pilot can depressurise the cabin by choice in modern aircraft. When would that be of use? What condition's/events would ever involve this choice? Would it ever be used in the event of a fire to starve it of oxygen?

J
African Civil Aviation Commission president "You don't want to fly out as a passenger and come back as cargo."
 
User avatar
Starlionblue
Posts: 17049
Joined: Fri Feb 27, 2004 9:54 pm

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 6:59 am

Fire?
.
.
.
.
.
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
pilotpip
Posts: 2820
Joined: Fri Sep 19, 2003 3:26 pm

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 7:12 am

Outflow valve being stuck completely closed resulting in a dangerously high pressure differential.
DMI
 
fr8mech
Posts: 6580
Joined: Mon Sep 26, 2005 9:00 am

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 8:38 am

Quoting Pilotpip (Reply 2):
Outflow valve being stuck completely closed resulting in a dangerously high pressure differential.

How would the flight crew depressurize the aircraft?

The only valid reason I could think of is smoke in the cabin. But, I think it would have to be a lot of smoke. But what about the fire causing the smoke? I'm thinking depressurization could starve the fire of oxygen...and all the passengers. But wait, the passengers will have oxygen. So, we will be feeding 100% pure oxygen into the masks, some of which will not be worn because there are extras. Will this feed the fire after the pressure equalizes? Who knows.

Maybe, a terrorist attempt to take the aircraft? Dump the pressure, pull a couple of quick, zero g manuvers and hope that in the confusion, the terrorist looses the upper hand.

Jules, the flight crew does have the ability to dump the cabin, but that ability exists because of the design of the system and not as an option for anything but the most extreme of situations.
When seconds count...the police are minutes away.
 
EMBQA
Posts: 7795
Joined: Sat Oct 25, 2003 3:52 am

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 8:51 am

Quoting Fr8mech (Reply 3):
How would the flight crew depressurize the aircraft?

Easy... The Emergency relief valve. Every aircraft I've even dealt with have two outflow valves. One is normally controlled, the other is controlled only by the dump switch.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 9:12 am

Quoting Pilotpip (Reply 2):
Outflow valve being stuck completely closed resulting in a dangerously high pressure differential.



Quoting Fr8mech (Reply 3):
How would the flight crew depressurize the aircraft?

Turn off the packs.

Would not want to be aboard.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 11:55 am

Why would the Crew want to do that.

Quoting Pilotpip (Reply 2):
Outflow valve being stuck completely closed resulting in a dangerously high pressure differential.

Modern Aircraft have built in backup systems to ensure it never occurs.
If it however does occur the Safety relief valves will Dump open.

Quoting EMBQA (Reply 4):
Easy... The Emergency relief valve. Every aircraft I've even dealt with have two outflow valves. One is normally controlled, the other is controlled only by the dump switch.

Are you refering to the MOFV & Fwd OFV.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
fr8mech
Posts: 6580
Joined: Mon Sep 26, 2005 9:00 am

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 12:06 pm

Quoting EMBQA (Reply 4):
Easy... The Emergency relief valve

Enlighten me. I've never heard of one. I know about pressure relief valves, but have never heard of an emergency relief valve that is controlled by a dump switch.
When seconds count...the police are minutes away.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 2:56 pm

There is no real reason to depressurize a passenger flight under "normal" circumstances. However, in the 744F the procedure for a main deck cargo fire is to depressurize the aircraft. Thus, no oxygen, no fire.
Fly fast, live slow
 
jush
Posts: 1495
Joined: Sat Apr 09, 2005 2:10 am

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 7:32 pm

Quoting Fr8mech (Reply 3):
Maybe, a terrorist attempt to take the aircraft? Dump the pressure, pull a couple of quick, zero g manuvers and hope that in the confusion, the terrorist looses the upper hand.

Well that's sounds like a kick ass maneuver, doesn't it.
That would be something for the airport movies i reckon.

Regds
jush
There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Sat Nov 19, 2005 10:12 pm

Quoting PhilSquares (Reply 8):
There is no real reason to depressurize a passenger flight under "normal" circumstances. However, in the 744F the procedure for a main deck cargo fire is to depressurize the aircraft. Thus, no oxygen, no fire.

Shouldn't there be a Main deck Isolation valve that shuts off packflow to the Main deck in case of Fire,rather than Depressurizing the Entire Aircraft.I thought that was an Important Equipment on Freighters.Which operators B747 Freighter are you referring to.Any details.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
fr8mech
Posts: 6580
Joined: Mon Sep 26, 2005 9:00 am

RE: Captain's Decision To Depressurise In Flight

Sun Nov 20, 2005 12:19 am

Quoting HAWK21M (Reply 10):
Shouldn't there be a Main deck Isolation valve that shuts off packflow to the Main deck in case of Fire,rather than Depressurizing the Entire Aircraft.I thought that was an Important Equipment on Freighters.Which operators B747 Freighter are you referring to.Any details.

You would then need 2 pressure vessels, or more to the point, a pressure bulkhead, with a door, between the main deck and the upperdeck. Expensive and heavy. When you are dealing with trained crew members and a handful of untrained (maybe), just open the outflow valves and let it go.

Quoting Jush (Reply 9):
Well that's sounds like a kick ass maneuver, doesn't it.
That would be something for the airport movies i reckon.

Actually, I was in Italy shortly after 9-11 and was reading the International Herald Tribune and a pilot (he was named as was the airline, but both escape me) suggested that the rules are now changed. A hijack will not be treated the same. The goal will not be to get the aircraft on the ground safely, it will be to deny the hijackers control of the aircraft. He just mentioned the use of negative g maneuvers and depressurization as an option.
When seconds count...the police are minutes away.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Captain's Decision To Depressurise In Flight

Sun Nov 20, 2005 6:49 am

Quoting HAWK21M (Reply 10):
Which operators B747 Freighter are you referring to.Any details.

All B744 built are like that. As explained, you'd have to have two separate pressure compartments to accomplish what you're talking about.
Fly fast, live slow
 
EMBQA
Posts: 7795
Joined: Sat Oct 25, 2003 3:52 am

RE: Captain's Decision To Depressurise In Flight

Sun Nov 20, 2005 9:44 am

Quoting Fr8Mech (Reply 7):
Enlighten me. I've never heard of one. I know about pressure relief valves, but have never heard of an emergency relief valve that is controlled by a dump switch.

Well, I don't know about what you have worked with as it may be different, but all the regional aircraft I've worked with have two valves. One is the pneumatic controlled valve and is used under normal conditions. The emergency relief valve is electronically controlled by the dump switch.

[Edited 2005-11-20 01:52:51]
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Sun Nov 20, 2005 5:38 pm

Quoting Fr8Mech (Reply 11):
You would then need 2 pressure vessels, or more to the point, a pressure bulkhead, with a door, between the main deck and the upperdeck.

Are you saying there is no Pressure Bulkhead on the B747 Freighter like the B737 Freighters.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Captain's Decision To Depressurise In Flight

Sun Nov 20, 2005 8:07 pm

Quoting HAWK21M (Reply 14):
Are you saying there is no Pressure Bulkhead on the B747 Freighter like the B737 Freighters.
regds

No, not at all. However, how are the lower cargo holds pressurized? The main deck, upper deck and the lower fad and aft cargo holds are all in the same pressure structure. So, if you depressurize the main deck, you do in effect depressurize the entire aircraft. There is no separate pressurization system for the lower cargo compartments.
Fly fast, live slow
 
vc10
Posts: 1339
Joined: Thu Nov 15, 2001 4:13 am

RE: Captain's Decision To Depressurise In Flight

Sun Nov 20, 2005 8:33 pm

I always thought that freighters only had a "strengthened" flight deck bulkhead but not a pressure bulkhead. Many freighters that carry animals also carry people in the back to care for them, and they might not be too pleased to be denied pressurization.

When talking about de-pressurizing an aircraft for fire reasons unless the memory is failing me [ and that could be the case ] were not the crew first supposed to descend the aircraft to a safe height before depressurizing the aircraft. To do this the air input has to be denied and then the remaining pressure dissipated by the override system [whether this be mechanical or otherwise]

Best avoid it little vc10
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Captain's Decision To Depressurise In Flight

Sun Nov 20, 2005 10:05 pm

Quoting VC10 (Reply 16):
I always thought that freighters only had a "strengthened" flight deck bulkhead

I can only speak of the 744. If you travel with grooms, there are extra O2 walkaround bottles put on the aircraft. If the groom(s) go to the main deck, then they have to take the O2 with them since there isn't any provision for that on the main deck. Remember, on the 744, they are seated in the upper deck.

As far as descending to a "safe" altitude, looking at the 747-400 QRH, is says "Climb of descent to 25,000 feet when conditons and terrain permit."
Fly fast, live slow
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 12:12 am

Quoting PhilSquares (Reply 15):
The main deck, upper deck and the lower fad and aft cargo holds are all in the same pressure structure. So, if you depressurize the main deck, you do in effect depressurize the entire aircraft. There is no separate pressurization system for the lower cargo compartments

What about the Cockpit & the Area between the Cockpit & the 9G bulkhead [The Supernumery Area].Isn't that zone Isolated by a Fire proof 9G bulkhead as on the B737 Freighters.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
CosmicCruiser
Posts: 2049
Joined: Tue Feb 22, 2005 3:01 am

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 12:51 am

Quoting HAWK21M (Reply 18):
What about the Cockpit & the Area between the Cockpit & the 9G bulkhead [The Supernumery Area

This depends on the a/c config. At Fedex we have some planes (only MD-10s I think) that have the rigid bulkhead and the rest (all MD-11s I believe) that just have the 9G net. However if you get a main cabin smoke alert the "SMOKE/OFF" switch on the AIR Panel is pushed shutting off air to the main cabin while still providing air to the cockpit creating a pressure barrier of sorts to keep smoke out of the cockpit. The procedure still calls for O2 100% and bringing the cabin alt to 25,000ft to starve any fire.
We had a crew which experienced one such main cabin cargo fire and put this checklist to the test. Everything went perfect for them but after ldg. the fire re-ignited when the cargo door was opened and the a/c burned to the ground.
This was Stewart NY which pix have been posted here.
 
User avatar
zeke
Posts: 9731
Joined: Thu Dec 14, 2006 1:42 pm

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 1:24 am

In a previous life I used to fly mentally unstable people for medical reason for them to get better help. They were chemically and physically restrained with a nurse and security person onboard. Despite these measures, and due to the high tolerance a lot of these people had to the chemicals one of them had a episode airborne where they removed themselves from the restraints and knocked out the nurse and security person out, and was choking the pilot in a head lock.

The nurse regained consciousness enough to inject the person to stop the attack.

Many times after that when transport similar persons I had a plan to dump the cabin at FL350, go on O2, and let everyone in the back black out.

In passenger jets, only reason would be for smoke or electrical fire to remove smoke from the cabin.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
julesmusician
Posts: 378
Joined: Sun Aug 28, 2005 3:25 am

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 1:45 am

It would be interesting to know medically what happens when you depressurise and how long it takes to black out - we now know this was the cause of the Helios airways crash in Greece. The captain didn't realise his controls were not set to pressurise automatically as they had been changed for maintenance on the system.. Warnings sounded in the cockpit and he thought it was for something else before blacking out along with the co-pilot. However on that flight there were people still concious and trying to control the aircraft. I believe that when you black out from no oxygen you reawake quickly when oxygen is restored?
African Civil Aviation Commission president "You don't want to fly out as a passenger and come back as cargo."
 
CosmicCruiser
Posts: 2049
Joined: Tue Feb 22, 2005 3:01 am

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 2:40 am

Quoting Julesmusician (Reply 21):
The captain didn't realise his controls were not set to pressurise automatically as they had been changed for maintenance on the system.. Warnings sounded in the cockpit and he thought it was for something else before blacking out along with the co-pilot.

Not only is that so outrageous and unbelieveable but from some tech folks at work I've heard there were even more unbelieveable stuff that went on in that a/c that I won't post here. No reason whatsoever that this accident occurred.
 
fr8mech
Posts: 6580
Joined: Mon Sep 26, 2005 9:00 am

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 6:13 am

Quoting HAWK21M (Reply 18):
What about the Cockpit & the Area between the Cockpit & the 9G bulkhead [The Supernumery Area].Isn't that zone Isolated by a Fire proof 9G bulkhead as on the B737 Freighters.
regds

A 9g bulkhead is still not a pressure bulkhead. It can be designed as such, but again, why add the cost and weight?

I'd also be careful using the term fireproof. The rigid 9g barrier is a smoke barrier, the heat of a fire impinging on it would quickly melt the seals around any pass through and render it ineffective.
When seconds count...the police are minutes away.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 6:39 am

Quoting HAWK21M (Reply 18):
What about the Cockpit & the Area between the Cockpit & the 9G bulkhead [The Supernumery Area].Isn't that zone Isolated by a Fire proof 9G bulkhead as on the B737 Freighters.

Again, we're talking about a 744F. There is no cargo in the upper deck, so no need for any type of 9G barrier.
Fly fast, live slow
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 12:40 pm

Quoting CosmicCruiser (Reply 22):
Not only is that so outrageous and unbelieveable but from some tech folks at work I've heard there were even more unbelieveable stuff that went on in that a/c that I won't post here. No reason whatsoever that this accident occurred.

Again the Underline Statement:- "Rules are to be followed".

Quoting PhilSquares (Reply 24):
There is no cargo in the upper deck, so no need for any type of 9G barrier

What about the B748.I know its too early.But Is it going to be a Three Layer cargo hold on the Freighter Version.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
User avatar
zeke
Posts: 9731
Joined: Thu Dec 14, 2006 1:42 pm

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 12:53 pm

Quoting Julesmusician (Reply 21):
It would be interesting to know medically what happens when you depressurise and how long it takes to black out - we now know this was the cause of the Helios airways crash in Greece.

Altitude Time of Useful Consciousness
FL 180 20 to 30 Min
FL 220 10 Min
FL 250 3 to 5 Min
FL 280 2.5 to 3 Min
FL 300 1 to 2 Min
FL 350 0.5 to 1 Min
FL 400 15 to 20 Sec
FL 430 9 to 12 Sec
FL 500 and above 9 to 12 Sec

http://wwwsam.brooks.af.mil/af/files...guide/HTML/Chapter_02.html#Hypoxia
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
XFSUgimpLB41X
Posts: 3960
Joined: Fri Aug 25, 2000 1:18 am

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 3:28 pm

We have an emergency depress button.... if you're at altitude it will dump the airplane to 14,250 +/- 750 feet or current altitude if you are below those.
Chicks dig winglets.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 3:40 pm

Quoting HAWK21M (Reply 25):
But Is it going to be a Three Layer cargo hold on the Freighter Version.
regds

I wouldn't forsee any drastic change to the basic structure at all. It appears as if every operator is very satisfied with the current configuration. The 748F will have the short hump in order to allow maximum number of 3 meter pallets.
Fly fast, live slow
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Mon Nov 21, 2005 8:30 pm

Quoting XFSUgimpLB41X (Reply 27):
We have an emergency depress button.... if you're at altitude it will dump the airplane to 14,250 +/- 750 feet or current altitude if you are below those

I presume the Dump valve is actually your MOV moved to Full open.Right or is there an Added Component.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
julesmusician
Posts: 378
Joined: Sun Aug 28, 2005 3:25 am

RE: Captain's Decision To Depressurise In Flight

Tue Nov 22, 2005 10:35 pm

What cabin altitiude do the oxygen masks drop down at automatically?
African Civil Aviation Commission president "You don't want to fly out as a passenger and come back as cargo."
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Tue Nov 22, 2005 11:08 pm

Quoting Julesmusician (Reply 30):
What cabin altitiude do the oxygen masks drop down at automatically?

If Im not mistaken 14,000 +/- 200 ft on a B737.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Tue Nov 22, 2005 11:08 pm

Quoting Julesmusician (Reply 30):
What cabin altitiude do the oxygen masks drop down at automatically?

If Im not mistaken 14,000 +/- 200 ft on a B737.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Tod
Posts: 1709
Joined: Sat Aug 28, 2004 6:51 am

RE: Captain's Decision To Depressurise In Flight

Wed Nov 23, 2005 12:04 am

Quoting Starlionblue (Reply 1):
Fire?

On the 742SF that I've worked on the smoke event procedures included shutting off packs, opening outflow valves and also opening a small air inlet forward of the flightdeck. This inlet provides for positive air pressure on the flight deck, keeping smoke from entering. This little inlet setup may seem a bit cheesy, but it's much cheaper than installing isolation valves on the mix manifold that would allow flight deck air to flow while shutting of main cabin air flow and it does work as intended.

Quoting PhilSquares (Reply 28):
The 748F will have the short hump in order to allow maximum number of 3 meter pallets.

How would the pallets get up there? New upperdeck side door?


Tod
 
User avatar
HAWK21M
Posts: 29867
Joined: Fri Jan 05, 2001 10:05 pm

RE: Captain's Decision To Depressurise In Flight

Wed Nov 23, 2005 2:00 am

Quoting Tod (Reply 33):
Quoting PhilSquares (Reply 28):
The 748F will have the short hump in order to allow maximum number of 3 meter pallets.

How would the pallets get up there? New upperdeck side door?

I think the Upper deck might be for Bulk.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
David L
Posts: 8547
Joined: Tue May 18, 1999 2:26 am

RE: Captain's Decision To Depressurise In Flight

Wed Nov 23, 2005 3:10 am

Quoting Tod (Reply 33):
Quoting PhilSquares (Reply 28):
The 748F will have the short hump in order to allow maximum number of 3 meter pallets.

How would the pallets get up there? New upperdeck side door?

Is this to do with the reduced ceiling height on the main deck immediately below the upper deck - shorter hump, more full height available on the main deck?
 
Tod
Posts: 1709
Joined: Sat Aug 28, 2004 6:51 am

RE: Captain's Decision To Depressurise In Flight

Wed Nov 23, 2005 3:35 am

Quoting David L (Reply 35):
shorter hump, more full height available on the main deck?

Yes, but you could still get the full height containers under the back of the longer upperdeck if it has supports replacing the upperdeck floorbeams aft of STA 800 like on the 744SF (or whatever it's called now).

Tod

Who is online

Users browsing this forum: No registered users and 15 guests