Re: altitude questions

From:         rdd@cactus.org (Robert Dorsett)
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date:         02 Nov 93 00:38:02 PST
References:   1 2 3
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In article <airliners.1993.692@ohare.Chicago.COM> kls@ohare.Chicago.COM (Karl Swartz) writes:
>>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.

My Airman's Information Manual says FL600 for the US Continental Control
Area.  It has FL450 for the jet routes (which I believe may be obsolete or
redefined; weren't these defined by VOR reception?).  But it's three years 
old: this might have been adjusted by the recent airspace redesignation/
consolidation.

>>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.

Often, this slot is not available.  For example, there's tremendous contention
over the North Atlantic.  Out of, oh, 50 crossings in a 747-200, I don't 
think we ever got above FL390.

>>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?

Pretty much.  Absolute ceiling is defined by a zero rate of climb.  Service
ceiling is a 100' rate of climb.  It's basically a power issue: how much
thrust your engines can produce in a steady state flight condition.  As
long as this exceeds your power required (drag), you'll climb.


>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.

The fuselage of a typical jet is capable of withstanding about 150% of
the overpressure relief, which is around 14.25 psi.  But I must emphasize
we're getting into "psycho test pilot" territory, here. :-)  I also
wouldn't recommend this on a 30-year-old, high-cycle 707. :-)


>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.

Yeah, I've heard a couple of 757 pilots gripe about how ATC's unable
to fully accomodate their capabilities.  I understand they can outclimb
just about anything by a factor of two. :-)




---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd