Re: 'Gas' used in tires of airliners?

From:         rickydik@ix.netcom.com (Ralph Ricks )
Organization: Netcom
Date:         22 Jan 96 03:24:16 
References:   1
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In <airliners.1996.31@ohare.Chicago.COM> bernhard@eurecom.fr (Christoph
Bernhardt) writes:
>A friend of mine recently claimed that airliner tires are filled with
>a special gas not just with normal (compressed) air. Is this true?

Yes, air contains 20% oxygen, just like what goes in a diesel engine.
Pressurize it to about 15 atmospheres, add some fuel such as vapors
from a very hot tire, and you have an explosion.  Just like a diesel,
you don't even need a spark.

The FAA has required 100% nitrogen (the other ~80% of air) to be used
in large aircraft tires since about 1974.  This was not a worldwide
rule due to FAA lack of authority.

In about 1985, a foreign 727-200 took off from Mexico City with about
170 pax, air in the tires, and a badly dragging brake.

Due to the hot, high conditions at MEX, the 727 climbs only 500fpm
until the gear and flaps are up, so the gear comes up right after
liftoff.  This time, however, the dragging brake continued to heat the
tire in the wheel well until it exploded, bringing the plane down with
total loss.

The above is what I remember from the NTSB report.

I believe that nitrogen is now a worldwide requirement, but not sure.
You cannot guarantee that all carriers everywhere never use air, so
keep that in mind when making your travel plans.

BTW, the only reason to use more expensive helium rather than nitrogen,
would be the difference in weight.  Helium, like nitrogen, is inert, so
safe.  It costs about $25 a year to carry a pound on an airliner, so
there would be some savings with helium.  You would have to weigh its
advantages, so to speak.

Ralph