View Full Version : Oxygen Packs and Bleed Air

27th Aug 2007, 16:18
Some time ago they had smoking on planes. I was once told that airlines used oxygen packs to supply the cabin with air. I have 2 questions:

Is it possible to use oxygen packs?

How many 747's would you say have the air toxin problem?

27th Aug 2007, 16:58
Not very sure what you're trying to say. Anyway, pax aircraft use airco packs which use air from the bleed air system, which comes basically from outside the cabin. oxygen is only used in emergency.

27th Aug 2007, 16:59

Perhaps you're on about air conditioning units, commonly referred to as 'packs'? They don't supply oxygen, though. They are used to decrease the temperature and moisture content of the bleed air from the engines/APU/external air cart, before this air reaches the cabin. Smoking near an oxygen source is not usually a good idea. :ooh:

Hope this helps. :)


27th Aug 2007, 17:02
Oops - you type faster'n me, Piper! :p

27th Aug 2007, 17:18
All Boeings and Airbuses currently in service use bleed air supplied from the engine compressors which is fed to air conditioning packs. The outlet from the A/C packs then supplies the cabin with conditioned air which is used to pressurise the aircraft cabin and maintain a comfortable temperature.

The A/C packs consist of heat exchangers and compressor/ turbine assemblies (operating on a 'boot-strap' cycle) which are used to cool the engine bleed air. Additional hot trim air fed directly from the engine compressors is fed to aircraft cabin zones that require additional heat compared to the heat requirement of the 'coolest' cabin zone which actually controls the outlet temperature of the A/C packs.

Some older designs such as the VC10 used freon packs coupled with Godfrey blowers (compressors) to condition the air to the cabin.

I believe aircraft such as the B.787 are designed to use electrically powered A/C systems as this is considered more efficient than the use of bleed air, but I stand to be corrected.

Oxygen is only supplied directly to the pax in the event of a cabin depressurisation. Modern designs tend to use oxygen which is generated chemically by oxygen generators directly above the pax. Older designs used compressed oxygen typically stored at high pressure in cylinders located in the area of the freight holds (very careful handling of anything to do with compressed oxygen is required, which is probably why a move to oxygen generators was then used). Oxygen is mandatory for pax above 14000 ft cabin altitudes and is normally automatically deployed. In addition portable oxygen bottles are stored in various locations around the aircraft cabin.

Oxygen for Flight Crew use is still supplied by compressed oxygen stored in cylinders.

How many 747's would you say have the air toxin problem?

Not quite sure what you are referring to here I'm afraid. I can tell you that in addition to air directly supplied to the aircraft cabin a portion of the air is recirculated for efficiency. There has been a lot of hype in the media over the last decade suggesting that this practice is dangerous, but it seems to have gone quiet on that front lately as the media have had equally daft ideas that have popped into their heads to be written about. (i.e DVT on aircraft, airline contribution to global warming - I could go on and on)

Hope this is of help.


27th Aug 2007, 18:11
Thanks Doodlebug,piper and eng, I want to be an airline pilot but that aerotoxins is putting me off at the moment but i will continue training up to cpl if poss. :)