How does fresh air get into an airplane?

Answer 1

The air on an airborne airplane isn't very fresh. Depending on the altitude, a percentage of the air is drawn in through some sort of vent that pressurizes it and puts it in the ventilation system. The other percentage is recirculated air that is drawn from the cabin, recooled, de-odored, and, I believe, "sanitized." This recirculation is the cause of much controversy, due to the outbreak of SARS on a plane flying from China on the Ides of March in 2003. The higher the altitude, the thinner the air outside the plane. And the less "fresh" air added to the mix, the more recirculated air is spread through the cabin. Hence, air in airplanes tend to smell stale.

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Another answer

Actually, the air is drawn in through the ENGINES. In a jet engine powered aircraft the engine is already compressing huge quantities of air and the cabin needs only a small portion of that air. The air is processed [cooled and cleaned] before being mixed with existing cabin air and ducted into the cabin. The quantitiy changes with altitude only with regard to change in barometric pressure i.e. the higher you fly, the "higher" the cabin is up to a maximum of 8000' of cabin altitude. The pressure is controlled by regulating the amount the cabin "leaks" air so there is quite a bit of air exchanged in the course of a normal flight. There has to be because the cabin is not totally air tight.

Another answer

I respond to the above answer relating to "Leaks in the cabin" specifically "The cabin is not totally air tight". The cabin must be totally air tight otherwise the aircraft would decompress with drastic results. Remember the De Havilland Comet amd all the break ups in flight due to decompression when the aircrfts skin sheared. I don't think much if any fresh air is drawn into the cabin, I reckon a large percentage is filtered, treated and recirculated. After a long flight as sure as hell I come down with flu about 4 days after the flight. It is no surprise to me with hundreds of people aboard a Boeing 777-300ER for 10 hours plus (Perth to Dubai). I would like to no much more