Re: altitude questions

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works
Date:         01 Nov 93 14:04:55 PST
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>Controlled airspace extends to FL600.

Sure it isn't FL650?  That's the number that comes to mind, though
I'll admit to not having the references at hand.

>41,000' is a common "maximum operating" number.  31,000-39,000' is
>more typical for medium and long-range flight.

For long-range flights they'll try to get as high as possible.  I've
flown LAX-LHR twice, first time was at FL390 and then earlier this
year at FL410.  In both cases we started off around FL350, climbing
to our final cruise after several hours.  I would assume this was due
to inability to reach the higher altitude until some fuel had been
burned off.

>I'd guess an absolute altitude for a commercial airliner around 50,000'.

What exactly do you mean by "absolute altitude?"  Pilots on oxygen,
light load, pushing it as hard as you can?

In most cases, the "service ceiling" is determined by the need to
maintain an 8,000' cabin altitude.  Generally the fuselage structure
and thus the pressure differential is the limiting factor, since a
stronger fuselage (thus greater pressure differential) weighs more.

Generally, longer range aircraft will have higher ceilings because
the longer cruise gives more time recoup the added cost of the longer
climb.  Newer aircraft tend to have higher ceilings, too, both for
efficiency and to get above more crowded airspaces.

I've only got a couple of examples handy -- the 737 family (35,000')
and the 757/767 (42,000').  I seem to recall that the 747 can go up
to 45,000'.

>See above.  You can use the same rule-of thumb as for short commuter hops
>in the US: Southwest, for example, tops at 21,000' in its 30-minute, 150-
>mile flight between Austin and Houston.

Though even on relatively short flights they can go remarkably high --
I've been on flights between SFO and LAX (337 miles) that got up to
FL370, maybe even some at FL390.  Cruise usually lasts less than ten
minutes on these flights!  BTW, it seems to me that all of these have
been on 757s, which have impressive climb rates even with a decent
load; on a short hop such as SFO-LAX they're truly amazing.

Karl Swartz	|INet		
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