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Several thoughts on this thread-


EXPECTED EXTERNAL ALTITUDES:

	While this it is generally true that 25-30,000 is a typical
cruising altitude of older aircraft, Boeing 747, in particular
routinely fly above 40,000.  I have been on at least one flight where
the co-pilot announced an altitude in excess of 50,000 feet, nominally
to avoid storms.

EXPECTED INTERNAL ALTITUDE: (PRESSURE/O2)

	One further point about the high altitude profile is that the
commercial airlines are changing the cabin pressure from the 'old'
standard of 5,000 feet up to 10,000 feet to save energy (fuel) in
heating the air into the cabin and at the same time, they are
lengthening the recirculation times (length of time between additions
of a new cabin volume of fresh (O2!) air).

RADIATION:

	Radiation is not a problem in practise.  While a 'normal' 2200
mile flight (transcontinental in the U.S.) is the equivalent of a
chest x-ray in radiation, the observed cancer rates are LOWER in
flight crews.  As of a month ago, the reason for this was unexplained,
other than a guess that perhaps that cosmic radiation wasn't as
harmful as ground level ionizing radiation.  i.e. they hadn't a clue
as to why.  By the way, the study involved large numbers of flight
crews.

	Personally, I'll wait 24 hours to desorb my gas loading.


		Peter David

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