Runway Lengths

Can anyone explain why runway lengths are sometimes "X thousand and
ONE feet" in length? I was just looking through a list of Iowa's
approximately 110 airports and 7 of them have runways that are "X
thousand and one feet" long.

Do runway manufacturing companies offer special deals like "Buy 5,000
feet of runway, get your next foot free!!!"

There's got to be a logical explanation - anyone know it?

(Ace Pilot) writes:

[about 5001 ft runways]

There's got to be a logical explanation - anyone know it?

They remeasured the runway after many dozen winters of frost heaves,
and found that it was 0.02% longer?


All the best,


David

Never thought about that before. However, my guess is that it is to make
sure that aircraft insurance requirements as to minimum runway lenght for
certain types is exceeded rather than simply met.

Anybody else?

Best regards,

Steve Robertson
N4732J 1967 Beechcraft A23-24 Musketeer

Ace Pilot wrote:

Can anyone explain why runway lengths are sometimes "X thousand and
ONE feet" in length? I was just looking through a list of Iowa's
approximately 110 airports and 7 of them have runways that are "X
thousand and one feet" long.

Do runway manufacturing companies offer special deals like "Buy 5,000
feet of runway, get your next foot free!!!"

There's got to be a logical explanation - anyone know it?

Just a wild guess, but I would think it is an artifact of the US
sectional/township system. Most property lines are along sectional lines (or
quarters of sectional lines) so runway length may be determined by what is
the longest diagonal that will fit on a square mile.

Either that or there is some FAA reg that involves runways of greater than
5000' that the designers wanted to take advantage of. But even there the reg
probably is based on the biggest runway you can fit on a section.

In article ,
C J Campbell wrote:
Just a wild guess, but I would think it is an artifact of the US
sectional/township system. Most property lines are along sectional lines (or
quarters of sectional lines) so runway length may be determined by what is
the longest diagonal that will fit on a square mile.

Either that or there is some FAA reg that involves runways of greater than
5000' that the designers wanted to take advantage of. But even there the reg
probably is based on the biggest runway you can fit on a section.

The main runway at BFI (Boeing Field) is also 10,001 ft. I have no
idea why. I always thought it was so that someone can claim: "Our runway
is over 10,000ft" without having to say equal to.

In article , C J Campbell
wrote:

Either that or there is some FAA reg that involves runways of greater than
5000' that the designers wanted to take advantage of. But even there the reg
probably is based on the biggest runway you can fit on a section.

I haven't looked recently, but it would be contained in Part 150.
I do know that 7000 foot runway is considered transport category, so I
suspect that insurance companies may require certain aircraft to be
operated from runways greater than x-thousand feet.

My guess it is a for insurance reasons. Morristown MMU runways are
listed as 3998 ft and 5999 feet. I bet this is to keep certain aircraft
out.

It's probably from the fact that the asphalt and/or concrete settles from
use and general settling (the former more than the latter). Much like a road
that eventually develops the speedbump-type elevations at the expansion
joints. The fact that "expansion" joints are needed and are named as such
should tell the entire story. I would even imagine that the runway length
expands soon after it's completed, again from the settling.

Marco



"Ace Pilot" wrote in message
om...
Can anyone explain why runway lengths are sometimes "X thousand and
ONE feet" in length? I was just looking through a list of Iowa's
approximately 110 airports and 7 of them have runways that are "X
thousand and one feet" long.

Do runway manufacturing companies offer special deals like "Buy 5,000
feet of runway, get your next foot free!!!"

There's got to be a logical explanation - anyone know it?



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Can anyone explain why runway lengths are sometimes "X thousand and
ONE feet" in length? I was just looking through a list of Iowa's
approximately 110 airports and 7 of them have runways that are "X
thousand and one feet" long.

Do runway manufacturing companies offer special deals like "Buy 5,000
feet of runway, get your next foot free!!!"

There's got to be a logical explanation - anyone know it?

According to FAA data, here is a count of runways grouped by the last digit
of the Runway Length.

Sorted by frequency
digit, count, %
0, 4333, 57.6%
5, 582, 7.7%
1, 549, 7.3%
9, 385, 5.1%
2, 379, 5.0%
8, 311, 4.1%
3, 274, 3.6%
7, 241, 3.2%
4, 234, 3.1%
6, 230, 3.1%

There does seem to be a statistically high percentage of runways with an
extra foot. Perhaps it's the 'fudge factor' the construction contractor
used to ensure they met specifications.

Chris
http://wayhoo.com/

Thanks for the analysis, Chris!

The idea that the contractor adds a little bit just to make sure they
don't fall short of what they are aiming for seems plausible. However,
I'll point out that your analysis shows the next most common ending
digit after 1 is 9. Makes me think contractors are missing their goal
by one foot almost as frequently as they are overshooting it by one
foot.

I don't know anything about the engineering of runways, but it would
come as a surprise to me that modern methods (laser range finding,
GPS, etc.) couldn't pin down a runway length to within several inches.
The fact that there are so many that end in 0 would seem to indicate
that contractors can make a runway the exact length they want to.

It would be interesting to see the runway specifications as spelled
out in the original construction contract.

"Wayhoo.com" wrote in message ...
Can anyone explain why runway lengths are sometimes "X thousand and
ONE feet" in length? I was just looking through a list of Iowa's
approximately 110 airports and 7 of them have runways that are "X
thousand and one feet" long.

Do runway manufacturing companies offer special deals like "Buy 5,000
feet of runway, get your next foot free!!!"

There's got to be a logical explanation - anyone know it?

According to FAA data, here is a count of runways grouped by the last digit
of the Runway Length.

Sorted by frequency
digit, count, %
0, 4333, 57.6%
5, 582, 7.7%
1, 549, 7.3%
9, 385, 5.1%
2, 379, 5.0%
8, 311, 4.1%
3, 274, 3.6%
7, 241, 3.2%
4, 234, 3.1%
6, 230, 3.1%

There does seem to be a statistically high percentage of runways with an
extra foot. Perhaps it's the 'fudge factor' the construction contractor
used to ensure they met specifications.

Chris
http://wayhoo.com/