Re: altitude questions

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         03 Nov 93 23:30:15 PST
References:   1
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In article <airliners.1993.687@ohare.chicago.com>,
 <campbjw@wkuvx1.bitnet> wrote:
>In the Nashville, TN area where I live, Air Traffic Control usually
>assigns commercial flights to altitude levels of 28000 to 33000 feet -
>what is the highest common flight level used and what is the maximum
>flight level the average commercial plane can attain?

I can't answer that one.

>       Related to
>that, what are the limiting factors in altitude attainment for
>commercial planes?

Two major factors spring to mind immediately.  One is the cabin pressure
differential.  Typically around 8 psi.  This limits most airliners to about
40,000 ft (DC-10s were designed for a higher cabin pressure differential -
about 10 psi if memory serves).  The other limit is the aircraft's
certification altitude.  The 757 for instance is certified to 42,000 ft
last I heard, but there is nothing physically preventing the airplane from
climbing higher (other than the cabin pressure consideration).

The technical performance limitations are mostly wing area and engine
thrust available.  These can be broken down into aspect ratio, span,
induced drag, or other factors/combination of factors depending on how one
wishes to approach the problem, what variables are ground-ruled as fixed,
etc.

>       Are these altitudes typical for trans-oceanic
>flights?  What are typical altitudes for European flights - I assume
>somewhat less since distances travelled are often less than in
>North America?  Does direction make much difference in altitude
>assignments?

Actually, European flights (as defined by flights originating in and
terminating in Europe) are very short compared to the average US flight
length.  We, Boeing, have had carriers who are strictly intra-European ask
for airplanes with much less range than our airplanes are capable of right
out of the box.  For instance, SAS I believe showed average flight lengths
somewhere near 300 miles.  American has average flight lengths somewhere
near double that.  Interestingly, I think Southwest has a relatively short
average flight length.  Karl probably has all the great data and could give
us real hard numbers.  :-)

Typical intra-European flight levels are around 27,000 ft, if the results
of one study I worked on can be generalized to this extent.


-- 
Terry
drinkard@bcstec.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."