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PizzaPolli
Topic Author
Posts: 234
Joined: Sun Oct 21, 2001 8:10 am

Runways And The ---->'s

Mon Jan 07, 2002 1:55 am

Ok, what is the reason that some runways are built with huge run ups i.e. JFK 13R/31L so that when planes take off they use the whole runway but when they land they touch down real far down? I assume that the area of the runway that has just the arrows ---> is not as reinforced as the rest of the runway but what is the point of doing this? What benfit does it have?
 
Accidentally
Posts: 614
Joined: Sun Dec 10, 2000 7:33 am

RE: Runways And The ---->'s

Mon Jan 07, 2002 2:14 am

I think what you're talking about is the threshhold...as far as I know it's there to help you clear obstacles, but don't quote me on that.
Indianapolis, IN
 
LY744
Posts: 5185
Joined: Sat Feb 03, 2001 11:55 pm

RE: Runways And The ---->'s

Mon Jan 07, 2002 4:19 am

Accidentally is right. It is a relocated threshold. Usually it's purpose is to help landing a/c clear obstacles (is it ever used for noise reduction purposes, i.e. when the approach is over residential areas?) that are close to that end of the runway. AFAIK, the runway construction is the same for the whole runway. The beginning of the actual threshold will be marked with green lights.

LY744.
Pacifism only works if EVERYBODY practices it
 
Guest

RE: Runways And The ---->'s

Mon Jan 07, 2002 4:29 am

The term used in the States is "Displaced Threshold"
 
ThirtyEcho
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Joined: Tue Jan 01, 2002 1:21 am

RE: Runways And The ---->'s

Mon Jan 07, 2002 6:03 am

You'll notice that the "touchdown zone" markings are way up the runway. They are two parallel bars, one on each side of the runway, that correspond to the ILS glideslope flare point. The -----> area is also the overrun coming from the other direction. The purpose is obstruction clearance, so it can be used for takeoffs but not landings.
 
Mr Spaceman
Posts: 2723
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RE: Runways And The ---->'s

Mon Jan 07, 2002 6:47 am

Hi guys.

A picture is worth a thousand words.


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Click here for full size photo!

Photo © Evan Gillespie



Click for large version
Click here for full size photo!

Photo © Daems Guy



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Click here for full size photo!

Photo © Daems Guy



Check out the size of the Touch Down Zone runway markings at Atlantic City Intl (ACY). I think they're the largest I've ever seen.


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Click here for full size photo!

Photo © Evan Gillespie



Just my 2 cents gentlmen.

Chris  Smile
"Just a minute while I re-invent myself"
 
Ralgha
Posts: 1589
Joined: Tue Nov 09, 1999 6:20 pm

RE: Runways And The ---->'s

Mon Jan 07, 2002 7:56 am

The arrows you are all discussing are part of displaced thresholds, NOT overruns. Displaced thresholds are used for obstical clearance and noise abatement on landing as previously stated. Overruns are generally not as strong as the main runway, marked by large yellow chevrons, and intended only for emergency use.

 Big thumbs up
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flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Runways And The ---->'s

Mon Jan 07, 2002 9:07 am

Just to add, the portion of runway before the marked displaced threshold can be used for takeoff, or landing rollout, just not touchdown.
 
LY744
Posts: 5185
Joined: Sat Feb 03, 2001 11:55 pm

RE: Runways And The ---->'s

Mon Jan 07, 2002 9:59 am

Talking about runway markings, can someone please explain the purpose of the big white rechtangles that are painted 1000' from the end ("beginning"?) of the treshold on runways with instrument approaches? I mean, I believe that they are supposed to mark the touchdown point or whatever, but do airplanes really land that far from the treshold? I mean, 1000' could come in handy!  Smile

LY744.
Pacifism only works if EVERYBODY practices it
 
Beefmoney
Posts: 1071
Joined: Tue Oct 10, 2000 2:16 am

RE: Runways And The ---->'s

Mon Jan 07, 2002 11:20 am

LY744,
Those markings are the "touchdown zone" or where the ILS glideslope meets the runway, airlines usually land a ways after that, even though a "perfect" landing would be in the zone. But greasing a landing causes them to land somtimes 1000' after that.
 
ejaymd11
Posts: 180
Joined: Thu Feb 22, 2001 8:04 am

RE: Runways And The ---->'s

Mon Jan 07, 2002 11:42 am

Displaced thresholds are also for when the ground is unsuitable for heavy operations. Here in Roanoke runway 24 is displaced because the runway needed to be lengthened but there is a tunnel in the way. So the front end of 24 is actualy above a tunnel.
 
TAA_Airbus
Posts: 491
Joined: Mon Nov 01, 1999 4:34 pm

RE: Runways And The ---->'s

Tue Jan 08, 2002 10:13 am

Back to the original question.
There are 2 common reasons, one is obstacle clearance on late finals, which everyone has said.
The other is the runway may not be strong enough in that area to arrest the descent of a heavy a/c.

Commonly you find that a runway is built, and then later on they add a displaced threshold, and consequently, it doesnt have the reinforcements that the original runway has.

 
n4khgirl
Posts: 449
Joined: Sat May 22, 1999 11:46 am

RE: Runways And The ---->'s

Tue Jan 08, 2002 11:01 am

Have they finished construction on rwy 24 in ROA yet? I heard they were gonna start working on 33 soon... or the taxiway leading to it infront of Piedmont

*Camille
 
ejaymd11
Posts: 180
Joined: Thu Feb 22, 2001 8:04 am

RE: Runways And The ---->'s

Wed Jan 09, 2002 6:08 am

TAA_Airbus thanks, N4KHGirl hey someone else from Roanoke Cool. As far as 24 I think all the work they where doing, I think is over, and I think they started doing something on 33 at night, but I'm not sure what and if they had finnished.

Ejay
 
Mr Spaceman
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: Runways And The ---->'s

Wed Jan 09, 2002 9:16 am

Hi guys.

Here's a good example of why a runway will have a displaced threshold due to an obstacle on short final. If I flew out of this airport, I'd sneak over to that big tree at night and quickly cut it down! hehehe. Then the final approach path would be much safer.

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Click here for full size photo!

Photo © Adam Cramer


Chris  Smile
"Just a minute while I re-invent myself"
 
Airbus_A340
Posts: 1441
Joined: Sat Mar 11, 2000 8:41 pm

RE: Runways And The ---->'s

Wed Jan 09, 2002 7:36 pm

I think the (closed) Hong Kong Kai Tak runway was also a good example of a displaced threshold because of the buildings located in Kowloon city. Not much could have prevented the noise, even height. Boy was it loud in Kowloon City, I remember every bit of it  Smile
Here's a good photo.

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Click here for full size photo!

Photo © Samuel Lo



Trevor Slack
 
MarkTPA
Posts: 94
Joined: Thu Jun 08, 2000 1:54 pm

RE: Runways And The ---->'s

Fri Jan 11, 2002 12:27 am

The arrows indicate a displaced threshold. It is not intended for touchdowns, usually not as strong as the rest of the runway. The other posts are correct, usually a displaced threshold is for obstacle clearance.

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