Re: Swissair MD-11 (SR 111, JFK-GVA) crash off Nova Scotia

Date:         07 Oct 98 02:49:09 
From:         Anonymous lo14 <>
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On 05 Oct 98 00:27:07 (John S. Maddaus)  wrote:
>Also, I remember reading an article dealing with the amount of outside
>air vs. recirculated air that is available throughout the ac.  I don't
>know whether this is true for all aircraft types, but the
>generalization was that the cockpit is approximately 90% ventilated
>from the outside, while first class is 50% and coach is down to 20%.

It's true for the MD-11, although the amount of new air introduced does
not vary with the seating.  It only varies with the total number of
passengers on board; you don't need as much new air on an empty
airplane as you do on a full one.

>My question then is can a pilot control the amount of new air vs.
>recirculated air in the cabin/cockpit, does it really vary (and this
>may simply be because of placement of intakes, vents, etc. and can a
>pilot completely shut off outside air entering the cabin in case of a

The "economy mode" just reduces the amount of outside air, it doesn't
shut it off.
Turning off the airconditioning "packs" would stop new air from
entering the airplane, but would also stop the pressurization.

And any air the passengers could breathe would also support a fire; the
oxygen masks passengers get mix ambient air (and smoke) with oxygen.
Only the crew has masks which exclude smoke.

Some *cargo* compartments depend on a lack of oxygen to snuff out a
fire, but no passenger compartment can do that.  That's because those
cargo compartments are inaccessible in flight.  You fight passenger
cabin fires with fire extinguishers.