WTFO? Cabin Air Question

[AbOvo]

OK so I'm drinking the morning coffee and reading the OC Metro magazine ( a local "business and lifestyle" mag). This month they have a nice article on how to stay fit while traveling. What caught my attention was a side bar titled "A Fresh Look at Stale Airline Air".

"Before 1978, all airplane passengers breathed fresh air. Airplane engines sucked in thin high-altitude air, compressed it, humidified it, and circulated it throughout the cabin. After the deregulation of the airline industry, airlines looked for ways to cut costs. The once-fresh air became a mix of fresh and recirculated air. Second hand air is often blamed for cold viruses and repiratory ailments - even the spread of diseases like tuberculosis and SARS."

Personally my understanding of pressurized aircraft systems has been that the air has always been a mix of recirculated and fresh air. Did airplanes "prior to 1978" just fly around with the outflow valves slightly open at all times to avoid recirculating air? I've been through ground school on the L-1011 and although it has been a few years I am pretty sure it recirculates air.

 

[Fearless Tower]

Not sure, but in the context of the article, it doesn't make a whole lot of sense....last I checked, air was free...I don't see how suddenly changing to re-circulated air would cut costs.

 

[onthebeach]

Recirculating cabin air saves fuel

Compressor air is tapped for cabin pressurization/ventilation. In the DC-9/MD-80/Boeing 717 design, cabin air flows through the cabin and out the outlflow valve...once in, once through, once out.

However, in other Boeing designs, the air is recirculated, i.e., mixed and blown through the various cabin sections several times before being exhausted through the outflow valves.

Recirculation reduces the need for bleed air for pressurization/ventilation, thereby increasing engine efficiency. In other words, less fuel is required since there is less bleed air demand.

An unfortunate side effect of recirc is that it appears to spread viruses and germs more in the cabin. Anecdotally, there is more spread of illnesses in recirc'ed cabins, although I'm not aware of any studies that support this.

 

[fxbat]

No air is not free, not in pressurized aircraft anyway. When you compress air it gets hot, very hot and you have to cool it.
The recalculation systems, save money by not robbing the engines of as much bleed air you would normally need to run the packs without the Rec. system.


Hears a good link for understanding the 737.
http://www.smartcockpit.com/b737/B737 AIRCOND.PDF
(cut & paste)

Scroll down to the bottom for system diagrams.

 

[fxbat]

Myth: Recirculation systems were not encountered prior to the 1980s.
Fact: Recirculation was commonplace before the jet age began. For example, the Boeing Stratocruiser of the late 1940s was equipped with an air recirculation system. In jet aircraft, filtered/recirculated air combined with outside air came in to use principally with the introduction of high-bypass-ratio fan engines. At Boeing, this began with the 747 back in 1970. Keep in mind, also, that air recirculation is common in building ventilation systems. Unlike buildings, however, jetliners have much better filtration, a much higher air-change rate and a much higher proportion of outside air.

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



Differences Between Older and Newer Cabin Air Systems

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

 

[retired guy]

Partially recirulated air is ok for the passengers and stew...er, flight attendents, but cockpit air is all fresh,unbreathed stuff.(note that I didn`t call it a "flight deck")

 

[FL420]

IIRC, and I'm too lazy to look it up, the A320 uses all fresh air while the B757 uses some fresh and some recirculated air.

 

[Stifler's Mom]

CRJ 700 uses recirculated air. The ATR flies so low and slow, we usually just opened the windows.

 

[CargoATRdriver]

CRJ 700 uses recirculated air. The ATR flies so low and slow, we usually just opened the windows.

I wish the windows opened on that pig...

 

[EagleRJ]

Airliners have never "humidified" the air. The corrosion problem would have been hard to cope with, as would have been keeping the windows fog-free.

Airflow in the cabin is generally top to bottom, so germs aren't spread from person to person. Any air that makes more than one trip around goes through hospital-quality HEPA filters, so any pathogens are minimized.

That article is full of crap