Runway Lengths

[Ace Pilot]

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?

[David Megginson]

(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

[Steve Robertson]

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?

[C J Campbell]

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.

['Vejita' S. Cousin]

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.

[EDR]

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.

[Thomas Ploch]

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.

[Marco Leon]

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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[Wayhoo.com]

> 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/

[Ace Pilot]

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/

[AES/newspost]

In article >,
(Ace Pilot) wrote:

> 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.

Can one _define_ the "start" and the "end" of a runway to within several
inches? (seems to me paving or blacktop would roll off over several
inch range)

[EDR]

[[ This message was both posted and mailed: see
the "To," "Cc," and "Newsgroups" headers for details. ]]


FAA Advisory circulars 150/5300-13 and 150/5325 privide explaination of
runway lengths required based on aircraft capabilities.

[G.R. Patterson III]

AES/newspost wrote:
>
> Can one _define_ the "start" and the "end" of a runway to within several
> inches? (seems to me paving or blacktop would roll off over several
> inch range)

Absolutely. You start the measuring wheel at the edge of the threshold mark and
stop it at pavement end.

George Patterson
To a pilot, altitude is like money - it is possible that having too much
could prove embarassing, but having too little is always fatal.

[StellaStar]

An Actual Fact (out of character for Usenet, but don't tell anybody) from a
friend who's an airport manager. I posed the group question, and his reply is:

"Most airports have that extra foot for insurance reasons. Aircraft insurance
policies for GA and corporate aircraft limit the operators to runways longer
than 3600 feet, 4000 feet, 5000 feet or whatever. So we build runways one foot
longer than what we think the insurance carriers require. The other requirement
that insurance carriers what are precision approaches. Aircraft owners of
turbines can get reduced premiums or are limited to use runways with precision
approaches."

[AES/newspost]

"G.R. Patterson III" wrote:

> AES/newspost wrote:
> >
> > Can one _define_ the "start" and the "end" of a runway to within several
> > inches? (seems to me paving or blacktop would roll off over several
> > inch range)
>
> Absolutely. You start the measuring wheel at the edge of the threshold mark
> and
> stop it at pavement end.

I obviously wasn't making any very great point here, other than that
"pavement end" might not be all that sharply defined, at least given my
observations of the edges of highway pavements, and more generally
measuring large physical things to 1 part in 5000, or 0.05% accuracy,
takes some care. To measure a 5000 foot runway to a precision of 1 foot
using a 2 foot diameter measuring wheel requires for example that the
diameter of said wheel be known to an accuracy of 5 mils = 0.005 inches,
including any dust or dirt layers it may pick up. I'd also note that if
the end of a 50 foot wide runway (I suppose that's a pretty wide runway
for some airports) is cut 1 degree off from perfectly square, the runway
is 1 foot longer on one side than on the other.

[Cub Driver]

On 21 Oct 2003 02:44:05 GMT, (StellaStar) wrote:

>An Actual Fact (out of character for Usenet, but don't tell anybody) from a
>friend who's an airport manager.

Bringing Actual Facts into a newsgroup discussion is an unforgivable
breach of Usenet ethics.

all the best -- Dan Ford
email: www.danford.net/letters.htm#9

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

[EDR]

[[ This message was both posted and mailed: see
the "To," "Cc," and "Newsgroups" headers for details. ]]

In article >,
AES/newspost > wrote:

> I obviously wasn't making any very great point here, other than that
> "pavement end" might not be all that sharply defined, at least given my
> observations of the edges of highway pavements, and more generally
> measuring large physical things to 1 part in 5000, or 0.05% accuracy,
> takes some care. To measure a 5000 foot runway to a precision of 1 foot
> using a 2 foot diameter measuring wheel requires for example that the
> diameter of said wheel be known to an accuracy of 5 mils = 0.005 inches,
> including any dust or dirt layers it may pick up. I'd also note that if
> the end of a 50 foot wide runway (I suppose that's a pretty wide runway
> for some airports) is cut 1 degree off from perfectly square, the runway
> is 1 foot longer on one side than on the other.

Differential GPS can measure down to 0.001 cm.
Laser rangefinding is comparable.

[Kevin McCue]

I would think it has more to do with the painting on the runway. The
length of the pavement seems to rarely correlate to the length of the
runway. ie over runs, thresholds, etc.

--
Kevin McCue
KRYN
'47 Luscombe 8E
Rans S-17 (for sale)




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[Roger Hamlett]

"Steve Robertson" > wrote in message
...
> 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,
I think you are correct.
The posters talking about the tarmac getting longer/shorter, or other
similar ideas, are ignoring the fact that the published 'runway length',
rarely matches that of the actual surface. Most airports, do not have the
threshold painted exactly on the ends of the runway surface. A local
airfield to me, exactly meets the other type of example being given (with a
runway 1 foot under a round number), yet the actual surface extends over 50
feet past the threshold markings. Hence the markings have been deliberately
placed inside the physical runway length, and an insurance/physical planning
limitation on particular aircraft types, would seem to be the only logical
explanation.

Best Wishes

> 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?
>

[Dan Thomas]

"Kevin McCue" > wrote in message >...
> I would think it has more to do with the painting on the runway. The
> length of the pavement seems to rarely correlate to the length of the
> runway. ie over runs, thresholds, etc.


Maybe heavy braking on a hot day stretches the pavement? ;-)

Dan