Re: Thickness of Runways

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         01 Dec 93 20:47:31 PST
References:   1 2
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In article <airliners.1993.777@ohare.chicago.com>,
Michael Yip <yip@sybase.com> wrote:

>I remember that thickness of the runway is one thing but the
>major factor really depends on the "distribution of weight"
>over the wheels of the aircraft.

The thickness of the runway depends primarily on the subgrade condition and
the Aircraft Classification Number (ACN) of the planes the airport owners
expect to serve.  The more swamplike the subgrade, the thicker the runway
needs to be to serve the same size airplane.  ACN is a measure of weight
distribution.  The corresponding measure for the pavement is the PCN, or
Pavement Classification Number.  The higher the ACN, in general, the
heavier the airplane.

>I forgot where I read it but the distribution of weight on a
>MD-80/DC-9 type of aircraft is not as even as, or not as "light"
>as a 747.  The 747 has more wheels to spread over its weight 
>while the MD-80/DC-9 has fewer to do the same.

I'm not sure what you really mean, but the MD-80 has an ACN of 30 or below,
and the venerable 747-400 has an ACN of over 60.  This is not a trivial
difference.  There are some airports which must be very careful of where
they allow 747s to operate because they are so heavy.  LAX is an example
that comes to mind.

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