CX says cabin air is safe.....really?

[turbspeed]

Taken from a newspaper cutting here in Malaysia, according to CX regional manager in PEN (WMKP) during a press conference cunducted by CX and backed by few regional airlines, that the cabin air is circulated every 3 mins using outside fresh air thus help eliminate the danger of contracting SARS to other fellow pax. Can someone back me up on this..... as far as we know, ALL contageous deseases case suffered by any pax are banned from entering any commercial flight right even before they step foot in the aircraft and in some cases they were offloaded! Correct me if I'm wrong again, are these somewhat steps to encourage ppl to travel or plain desperate act in bull****ting the travellers?
I know how bad the outbreak has affected all the airlines ( not just to CX ) but is this really true? And if it is safe to fly with SARS, what's the stand on other contageous deseases such as simple Chicken Pox, to name the least....? I'm open to any comment...... go ahead guys!

[Lou Scannon]

Two points:
Firstly there is a list of those medical conditions that a passenger is not allowed to board an aircraft with because of the possibilty of their being contagious to the other passengers. These will usually include relatively minor ailments such as chicken pox to the most serious ones such as open tuberculosis of the lungs. No doubt SARS has been added to these lists.

Secondly it would be most unusual for the air in the cabin to be changed every three minutes. Most aircraft now recirculate the cabin air through some pretty inefficient filters and only take in a percentage of fresh air to maintain the cabin pressure. Have the airlines in question given a guarantee that the "re-circ" fans will be switched off thereby ensuring clean fresh air is indeed, circulated?

Now consider the problem of passengers who board not realising that they are infectious and also that the cabin air is recirculated.
It may not be a healthy situation but the risks are still minimal and probably less than the risk of contracting malaria on the way to the airport!

Nothing in life is without risk, but switching off the recirc fans when operating in certain areas would seem a good idea.

[turbspeed]

Lou,

I really thought so, another thing that was mentioned during the conference was that the filters are anti-bacterial based and who are they trying to bull here......

[Cathar]

The House of Lords Science and Technology Committee held an inquiry into air travel and health in 2000. Their findings on the issue of recirculation of air and the transmission of disease are set out below:

1.61 The typical cabin air flow of 20 cfm of air per occupant equates to a full change of cabin air every 2 to 3 minutes, i.e. 20 to 30 times per hour. As half of the air being changed is re-circulated cabin air, this is equivalent to an entire exchange of cabin air with fresh air 10 to 15 times per hour. (Paragraph 5.5)

1.74 On the evidence we have been given, it seems to us that the risk of transmission of infection due specifically to being in the aircraft cabin environment is no greater than elsewhere, provided circulation and filtration systems are working properly. Given the evident success in avoiding transmission of major infections, we do not agree with those who seem keen to attribute any travel-related infectious ailment to augmented transmission within the aircraft cabin environment. (Paragraph 7.17)

1.75 The theory, the facts and the vast majority of our specialist witnesses all support the conclusion that HEPA filtration, if properly installed and maintained, should remove the possibility of cross-infection that would otherwise exist in re- circulatory cabin air systems. We agree that, on the evidence presented to us, the modern aircraft cabin environment generally poses no greater risk of transmission of infection between its occupants than crowded situations elsewhere - and may, indeed, be safer than most of them. (Paragraph 7.25)

http://www.parliament.the-stationery.../121/12102.htm

[Lou Scannon]

The House of Lords may have a valid point here but I can remember when smoking was allowed on all flights. The cabin would rapidly fill with the smoke from burning cigarettes to the point that even the smokers amongst the cabin crew would complain.

According to their Nobel Lordships, this was impossible as the entire air was changed every three minutes.

And yet, when the flight deck turned off the re-circ fans the cabin smoke would clear in about two minutes.

QED, re-circ fans do what is says on the can-and it doesn't say that it changes the air every three minutes. It says that they significantly reduce the need for bleed air off the compressors thereby decreasing fuel burn.

As to the filters, can we hear the views of the ground engineers who actually see them and hopefully get to change them? As far as I can remember, they filter out very little.

[Dan Winterland]

There's a lot of b@llocks about cabin air - especially from the press. The only figures I remember from my type tech are for the B747-400. The flow of cabin air with all 3 packs at high flow means the whole cabin air gets changed in about 8 minutes. In the cruise with 3 packs at low flow and all the recirc fans on, the air is changes every 12 minutes. Compared with the average operating theatre (every 20 minutes) or an average office block (every hour) this isn't bad. Also, the recirculated air is passed through the same type of filters used in operating theatres - although how often they are changed is a different matter.

I think these figures are correct, but my 744 type tech was a while and two types ago. Cornish Jack will know the correct figures if I'm wrong.

[Colosseo]

According to a TIME megazine report on SARS, there was speculation that the cr@p might have been transmitted in the the A/C's toilets.

[HotDog]

I do believe modern HEPA filtration is efficient enough to prevent airborne infections in the cabin, even with recirc fans operating. It can not prevent infections if your seatmate happens to be infected and sneezes in your face. Nor can it prevent infection from toilet door handles or any common equipment that passengers might come in contact with.

[purr]

It is important to keep the recircs on as they are effective in diluting the virus thus making it difficult from spreading beyond two rows either side.By the time the air reaches the flt deck it is pretty diluted.And yes I heard about the filters too .Hopefully they are cleaned regularly.

[Avago]

If you don't believe Cathay, perhaps you could try the following link for Boeing's view on cabin air quality:

http://www.boeing.com/commercial/cabinair/index.html

[HotDog]

Dan, they most likely didn't tell you all the facts during your 744 conversion as the philosophy is "need to know" for pilots. Only the flight engineers delved deeper into the intricacies of systems, alas no more F/Es to enlighten you on the 744. However on the question of HEPA filters and how often they are replaced by maintenance, see the following.

Myth: When the air filters get dirty, they're no longer effective.

Fact: The high efficiency filter, in particular, actually becomes more effective because the trapped particles make it more difficult for other matter to pass through. The filters are replaced at regular maintenance intervals. If several intervals were missed, and an abnormally heavy build-up of particles occurred, the only effect would be reduced flow of the recirculated air -- but whatever air did pass through would be extremely well filtered. In any case, the filters do not affect the flow of the outside-air portion.

So my advice, please keep those recirc fans on, as it says in VOL.3

[bonajet]

I cannot make up my mind Turbspeed whether you are a journalist, a rabble rouser or just had a troubled childhood. On a similar topic (ba crews, is this really necessary?), you were quoting that all the hospitals were full in Hong Kong and not admitting any foreigners. That complete untruth was answered well and firmly by Christep but here you go again! It is possible to frighten people over anything as ignorance and gullibility is a world wide problem – please stop adding to it.

I quote our company guidelines below in an attempt to explain the system.

“The recirculation system supplements airflow and improves ventilation. These fans are automatically controlled based on flight phase and air conditioning pack supply, they optimize airflow during all phases of flight.

Each filter plenum has a HEPA (High Efficiency Particulate Air) filter element attached to it, should the fans be switched off the filters would effectively be removed for the system. The recirculation system is the only system that filters the air inside the cabin. The HEPA filters have a 99.97% efficiency rating, which effectively filter out bacteria.

The recirculation fans assist in providing cooling, particularly during ground operations, by supplementing cabin airflow. Airbus and Boeing both recommend that these fans remain switched on for maximum cabin ventilation. Recirculation fans must not be switched off, unless so required by a non-normal condition. The pack flow rate is regulated automatically, no manual intervention is normally required. However, crew may select pack to high flow should hot or humid conditions in the cabin warrant this selection.
In flight fresh air is introduced into the cabin and mixed with filtered air in a 50:50 proportion. The volume of fresh air introduced is such that the entire volume of air within the cabin is replaced every 3-5 minutes. An office building’s air-conditioning system by comparison will typically mix only 10% to 18% of fresh air with recycled air.

The dry air in aircraft cabins is inhospitable to germs, as most thrive in a moist environment. Whenever groups of people congregate in close proximity there will be a risk of disease transmission. However, the air quality in an aircraft provides no more risk than other forms of public transport. The airline industry's experience with other transmissible respiratory diseases supports the view that air travel poses minimal risk of infection.”



Let’s not get hysterical and talk ourselves back into the Stone Age. There are risks all around in life – assess them correctly and stop jumping at every loud noise.

[Anti-ice]

Any engineers here that know how often the filters are changed then ? ? ? ?

Is it strictly to the manufacturers guidelines??

Also, how have people contracted viruses / conditions onboard in the past then ,that have been well documented ? ?

I'm sure that i've also seen somewhere that the dryness of the cabin air , (and getting drier on newer aircraft) adds to the effectiveness of these germs/bugs/viruses.

[Avago]

Anti-ice:

As to your last question, my understanding is that the low humidity inside aircraft cabins is extremely INHOSPITABLE to these viruses, ie they die real quick.

[stickyb]

Just a point about the frequency of changing the cabin air, from my experience of modelling fluid dynamics.

To say that the air is changed every 8 minutes or whatever may be true in terms of volume, but is not true of actual air molecules. It would be more correct to say that half the air is changed twice every 8 minutes, or even that a quarter of the air is changed 4 times every 8 minutes.

You can guarantee that at least some of the air inside the cabin at the end of a long haul flight is still the original.

[HotDog]

Don't see how you can guarantee that unless you are privy to the manufacturers test data. But maybe you are?

[Cornish Jack]

Here we go, AGAIN!!
Tubspeed. if the thought of recirc. air gives you a problem, whatever you do, don't go near an operating theatre - they use the same filters. Personally, I'd prefer the recircs - can't stand hospitals
G'day Dan W, hope all goes well.
HotDog - As it happens, having taught both F/Es and Pilots, I tried to ensure that they both got the same information - indeed, on the 747 'Trabant' they actually did the same tech. course, the same exams etc. Thereafter, the F/Es would (of course) tuck themselves in for early nights, cuddling that esoteric volume of technical delights, the 'QuaintAss' F/Es 747 handbook. If I ever feel the need, I'll dig out my copy to reassure myself of how rivetting it was.

[stickyb]

Hotdog - yes, I can guarantee it. I am not doubting the manufacturers test data, just adding my knowledge of fluid dynamics modelling.

The volume of air changed may be equivalent to a cabinful every 8 minutes, but that does not mean every molecule changed once every 8 minutes

[HotDog]

stickyb, You may be right about a few missing air molecules. I have sent you an article on modern ECS systems, written by the Boeing Company. It's rather long so I had to break it up into four parts to fit the private message rules. Hope you don't mind but you might find it of interest from a fluid dynamics point of view. Cheers, HD.

[stickyb]

Thanks HotDog, the article is good stuff, and I would not disagree in any way with the statements it makes about the quality or quantity of air. However, my statements are based on a much lower level view, the molecular level, and we can both be right.