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rmoore7734
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Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 2:12 am

Why the dip on runway 8R/26L @ ATL

Why did they not make it relatively flat the whole length when origionally built ?

[Edited 2012-08-23 19:20:25]

[Edited 2012-08-23 19:29:43]
 
GlobalMoose
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 3:08 am

I'm assuming your question is why the runway isn't a 0% grade the entire length of the runway-

I'm not an airfield engineer, but the biggest reason, I imagine, is cost. We have the technology to level land as needed but the amount of effort (thus cost) required to make a runway exactly flat when a -0.6% grade works perfectly fine.

As an aside, there are a few issues that a non-level (0%) runway presents to a pilot. To name two:

TOLD - my box (FMC, FMGC, MC, whatever you want to call it) usually (key word) stores the percent grade of every runway in its database to run TOLD calculations. Even a small grade can have an effect on take off and landing distance required.

Runway illusions - when pilots fly into one field with regularity, they become accustomed to a specific sight picture of the runway. When the dimensions of the runway change (length, width, and even an up slope or down slope) the sight picture is slightly different. This can result in the pilot flaring early, too late, or in the case of a sloping runway they could flare at the appropriate height above the runway but due an up slope have a bit of a firm landing or float the landing a bit long as in the case of a down slope. Hopefully the pilot performs the necessary airfield study prior to the descent to prevent this!

That is a bit of a pilot perspective, hopefully there are some civil engineers on the forum!
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Starlionblue
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 3:43 am

Apart from the cost of absolutely level grade (runways are thick and expensive as it is), there's drainage to thing about. Completely flat surfaces are not great in the rain.
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rfields5421
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 4:15 am

None of the runways at KATL appear to be perfectly flat - 10/28 is the closest to level with a 2 ft elevation change between ends

From looking that the FAA airport diagram - http://155.178.201.160/d-tpp/1208/00026AD.PDF

Rwy 8L/26R - the 8L end is 25 feet higher than the 26R end - the slope is 0.6% down from the 8L end
Rwy 8R/26L - the 8R end is 9 feet higher than 8L and 29 feet higher than the 26L end - the slope from the 8R end is 1.0% down and 0.4% down from the 26L end

Rwy 9L/27R - the 9L end is 42 feet higher than the 27R end - the slope is 0.3% down on 9L from about 1/3 way down the runway and 0.4% up from the 27R end
Rwy 9R/27L - the 9R end is 41 feet higher than the 27L end - the slope is 0.5% down and up from the respective ends

The 9R end is the higherst elevation point 1,026 ft

Now as to why the dip - it is probably related to the underlying terrain. It is EXPENSIVE to fill a large area to bring up the elevation, create new drainage routes. Additionall, the time necessary to settle the fill area might have been an unacceptable delay in completion of the runway.

Remember ATL has been an airport since 1926. It was not a 'fresh build' like DFW, DEN or CDG.

Something I found

Quote:
In March 1962 the longest runway (9/27, now 8R) was 7860 ft; runway 3 was 5505 ft and runway 15 was 7220 ft.

so obviously the airport has gone through several rebuilds while still having to keep runways open for operations.
 
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rmoore7734
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 11:39 am

I see that the delta tech-ops hangers are sitting lower on airfield than rest of terminals. Perhaps part of dip is so a/c can get to the delta hangers but then again perhaps just the taxiway would need that and the runway no dip ? Thanks for replies above.
 
atlamt
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 2:31 pm

It's mostly due to the original slope of the land. There is a downward slope to the east. Also the airport was built over the Flint river which now runs under the field. It's source is just to the north. I'm sure it affected how the land was sloped. The east end of all the runways and taxiways was built up to maintain the slope within the regulations. The ramp and concourses are probably the flattest part of the airport but they too required a lot of fill. At the east end of concourse F's ramp it drops off 50+ feet to the cargo and catering facility below.
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rmoore7734
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 3:35 pm

Quoting atlamt (Reply 5):
the airport was built over the Flint river which now runs under the field.

How convenient to have the Flint as a natural run-off for drainage. Seems like the hilly north Georgia terrain is not so disadvantaged after all to have a major airport compared to board flat OKC airport. Makes you wonder how they manage the run-off from their airfield.

I can think of another big advantage is runway 10-28 is elevated to the same level as the terminals. I'm thinking if I-285 were not already lower relative to the midfield area that they would have had to re-route the interstate or bore a tunnel under 10-28 instead. Probably more expensive as well.
 
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 3:48 pm

Quoting Starlionblue (Reply 2):
Apart from the cost of absolutely level grade (runways are thick and expensive as it is), there's drainage to thing about. Completely flat surfaces are not great in the rain.

Not sure, but I'd tend to doubt they rely on the lengthwise grade of a runway for drainage (after all, there are plenty of nearly flat runways in existence).

That's why they are sloped to the sides and grooved.
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canoecarrier
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 5:49 pm

the post system doesn't seem to like me today. I can only get two lines in before it's cut off.

[Edited 2012-08-24 10:53:23]

[Edited 2012-08-24 10:55:02]
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N126DL
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RE: Why The Dip On Runway 8R/26L @ ATL

Fri Aug 24, 2012 9:12 pm

Are they making a new taxiway intersection with 26L? I noticed the construction equipment last week during my stopover.
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rmoore7734
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RE: Why The Dip On Runway 8R/26L @ ATL

Sat Aug 25, 2012 3:38 pm

Quoting N126DL (Reply 9):
Are they making a new taxiway intersection with 26L? I noticed the construction equipment last week during my stopover.

"The $40 million project included the runway extension, extensions of taxiways L and M, and the creation of taxiways LA, LB and LC. These three additional taxiways give departing aircraft triple access to Runway 27R, which increases carriers' and air traffic controllers' flexibility in managing airfield operations and should help reduce departure delays. "

source: http://avstop.com/July_2012/runway_e...ternational_airport_efficiency.htm
 
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RE: Why The Dip On Runway 8R/26L @ ATL

Sat Aug 25, 2012 4:37 pm

Quoting rmoore7734 (Reply 6):
How convenient to have the Flint as a natural run-off for drainage. Seems like the hilly north Georgia terrain is not so disadvantaged after all to have a major airport compared to board flat OKC airport. Makes you wonder how they manage the run-off from their airfield.

Board flat? How so? Going off memory here, but one of our runways (17L/35R) is identified in a runway extension plan as requiring regrading midfield because of an elevation change -- if they lengthen the runway, the elevation change midfield would prevent seeing the other end of the runway from either side.

http://155.178.201.160/d-tpp/1208/00301AD.PDF

Look at 17L/35R. There is a 3 foot elevation difference from either side, but a 12 foot elevation change midfield. There is also a 19 foot elevation change on 17R/35L end to end. And a 20 foot elevation change from the thresholds of 35L/R (separated by 1 mile). And a 10 foot 3% grade elevation change from the airfield elevation point to the threshold of 31, a distance of 2,500 feet.

If you have ever spent any amount of time at OKC it is actually not very flat at all. It is nearly impossible to take pictures of airplanes from ground level at OKC, the elevation changes usually cut off half of the fuselage from just about anywhere.
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rmoore7734
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RE: Why The Dip On Runway 8R/26L @ ATL

Sun Aug 26, 2012 2:00 am

Quoting jetmatt777 (Reply 11):
Board flat? How so? Going off memory here, but one of our runways (17L/35R) is identified in a runway extension plan as requiring regrading midfield because of an elevation change -- if they lengthen the runway, the elevation change midfield would prevent seeing the other end of the runway from either side.

I was on I-44 parallel to the field & it appeared board flat visually. Did not realize the nearly 20 foot plus change. But then again I was going probably 70 MPH    thru there & glanced quickly at it. Thanks for clarifying. As a side note ended putting over 3000 miles plus on rental car going all over that state from top to bottom & east and west to the state borders doing a RF field survey.
 
jetmatt777
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RE: Why The Dip On Runway 8R/26L @ ATL

Sun Aug 26, 2012 3:55 am

Quoting rmoore7734 (Reply 12):
I was on I-44 parallel to the field & it appeared board flat visually. Did not realize the nearly 20 foot plus change. But then again I was going probably 70 MPH    thru there & glanced quickly at it. Thanks for clarifying. As a side note ended putting over 3000 miles plus on rental car going all over that state from top to bottom & east and west to the state borders doing a RF field survey.

Oklahoma appears flat....but really the elevation changes are rolling hills and not the traditional cresting-hill, although we do have cresting-hills as well. (for lack of a better term) You don't realize how "not flat" Oklahoma is until you have an ice storm....and realize every single street is sloped up/down by pretty decent amounts. All perception! 
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rmoore7734
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RE: Why The Dip On Runway 8R/26L @ ATL

Sun Aug 26, 2012 12:58 pm

Quoting jetmatt777 (Reply 13):
Oklahoma appears flat....but really the elevation changes are rolling hills and not the traditional cresting-hill, although we do have cresting-hills as well. (for lack of a better term) You don't realize how "not flat" Oklahoma is until you have an ice storm....and realize every single street is sloped up/down by pretty decent amounts. All perception! 

I have learned my lesson though... will check FAA airport diagrams before I comment on how flat I think an airport is.   
 
rfields5421
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RE: Why The Dip On Runway 8R/26L @ ATL

Sun Aug 26, 2012 4:18 pm

Quoting rmoore7734 (Reply 14):
check FAA airport diagrams

On another thread about a year ago - someone said it was impossible to have a 100 ft elevation change on a runway - so I posted the LAS diagram - with 146 ft change on 7L/25R.
 
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rmoore7734
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RE: Why The Dip On Runway 8R/26L @ ATL

Sun Aug 26, 2012 6:12 pm

Quoting rfields5421 (Reply 15):
On another thread about a year ago - someone said it was impossible to have a 100 ft elevation change on a runway - so I posted the LAS diagram - with 146 ft change on 7L/25R.

I would not have believed it till I checked it out    http://upload.wikimedia.org/wikipedi...d/d2/McCarran_Airport_Diagram.svg. Thanks

  

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